2012 Zhu, Calcium a bone

Review

Calcium and bone

Kun Zhu⁎, Richard L. Prince
Department of Endocrinology and Diabetes, Sir Charles Gairdner Hospital, Perth, WA, Australia
School of Medicine and Pharmacology, University of Western Australia, Perth, WA, Australia

abstractarticle info
Article history:

Received 23 December 2011

Received in revised form 4 May 2012

Accepted 8 May 2012
Available online 17 May 2012Keywords:Calcium intakeCalcium supplementationBone mineral densityPeak bone massFracture

Children

Adolescents

Older people
Objective:Evaluate the role of calcium on bone health.
Methods:Review of literatures on calcium and bone development during childhood and bone health in
adulthood and older age.
Results:Calcium intake in⁎uences skeletal calcium retention during growth and thus affects peak bone
mass achieved in early adulthood. Increased calcium intake is associated with increased bone mineral accre-
tion rate up to a threshold level in all ethnic groups. The minimum intake to achieve maximal retention is
1140 mg/day for white boys and 1300 mg/day for white girls. Calcium also plays a role in preventing bone
loss and osteoporotic fractures in later life. Meta-analyses report that calcium supplementation reduce
bone loss by 0.5–1.2% and the risk of fracture of all types by at least 10% in older people. Low calcium intake
is a widespread problem across countries and age groups.
Conclusion:Adequatecalciumintakethroughoutlifetimeisimportantforbonehealthandthepreventionof
osteoporosis and related fractures.
© 2012 The Canadian Society of Clinical Chemists. Published by Elsevier Inc. All rights reserved.

Contents
Introduction................................................................ 937
Calcium and bone development during childhood and adolescence....................................... 937
Calcium and dairy intake and bone mineral accretion........................................... 937
Calcium retention in children and adolescents in cross-cultural studies................................... 937
Calcium and bone in young adults...................................................... 937
Calcium and bone in older age........................................................ 938
The effect of calcium in preventing bone loss............................................... 938
The effects of calcium in preventing fracture............................................... 938
Calcium and hip fracture risk...................................................... 938
Meeting calcium requirement........................................................ 939
Calcium intake in children and older adults................................................ 939
Children and adolescents..................................................... 939
Older people........................................................... 939
Intestinal factors affecting intestinal calcium absorption.......................................... 939
Lactose............................................................. 939
Fiber.............................................................. 939
Protein............................................................. 939
Achlorhydria........................................................... 940
Calcium supplementation........................................................ 940
Controversiesoncalciumsupplementationandvasculardiseaserisk....................................... 940
Conclusions................................................................. 941
References................................................................. 941Clinical Biochemistry 45 (2012) 936–942
⁎Corresponding author at: Department of Endocrinology and Diabetes, Sir Charles Gairdner Hospital, Nedlands, WA 6009, Australia. Fax: +61 8 9346 1317.
E-mail addresses:kun.zhu@uwa.edu.au(K. Zhu),richard.prince@uwa.edu.au(R.L. Prince).
0009-9120/$–see front matter © 2012 The Canadian Society of Clinical Chemists. Published by Elsevier Inc. All rights reserved.
doi:10.1016/j.clinbiochem.2012.05.006Contents lists available atSciVerse ScienceDirect

Clinical Biochemistry
journal homepage: www.elsevier.com/locate/clinbiochem

Introduction
The adult human body contains around 1kg calcium on average,
more than 99% of which exists in bone and teeth. In bone, calcium
exists in mineral form as hydroxyapatite [Ca

(PO

(OH)

Calcium

infl
uences bone strength through its effect on bone mass. Calcium
intake is one of the important modifiable environmental factors for
thenormaldevelopmentoftheskeletonduringgrowthandthemain-
tenance of bone mass in later life.
Calciumandbonedevelopmentduringchildhoodandadolescence
Calcium and dairy intake and bone mineral accretion
Bone mineral accretion during growth is a major determinant of
peak bone mass, which is associatedwith the risk of developing oste-
oporosis in older age. The peri-pubertal and pubertal years are a
critical period for bone mineral accretion, with around 39% of young
adult total body bone mineral gained in the 4years surrounding
peak height velocity[1]. Many factors, including genetics, gender,
endocrine and nutritional factors influence the attainment of peak
bone mass. Most epidemiologic and randomised studies of calcium
intake have been undertaken in subjects with diets adequate in other
nutrients such asprotein, carbohydrate and fat.
Calcium intake influences skeletal calcium retention during bone
growth and thus plays a role in peak bone mass achieved in early
adulthood. Longitudinal studies in Canadian boys[2]and Chinese
girls[3]have shown that calcium intake was a minor but significant
predictor of total body bone mass. Inadequate calcium intake during
growing period could compromise peak bone mass attained at skele-
tal maturityand thuspredisposeindividualsto increased risk of oste-
oporotic fracture in later life. A study of 3251 Caucasian women from
thethirdAmericanNationalHealthandNutritionExaminationsurvey
showedthatwomenwithlowmilkintakeduringchildhoodandadoles-
cencehadlowbonedensityinadulthoodandgreaterriskoffracture[4.
Inaddition,lowbonemassmayalsocontributetochildhoodfracture.A
report in New Zealand children showed that those who avoided cow's
milkhad 1.7 times higher riskforpre-pubertalfracture[5.
The majority of intervention studies with dairy foods or calcium
supplement in children and adolescents from different ethnic back-
grounds have shown positive effects on bone mineral accretion at
one or more of the sites measured[6–

12]. Two meta-analyses evalu-
atedtheeffectsofcalciumsupplementationonbonemassinchildren.
Thefirstmeta-analysis whichincluded19 studies(n=2859)showed
that calcium supplementation had a significant effect on total body
bone mineral content (BMC) (standardised mean difference 0.14, 95%
CI 0.01–0.27) and forearm bone mineral density (BMD) (0.14, 95% CI
0.04–0.24), but no effect on BMD at the femoral neck or lumbar spine
[13. The other meta-analysis included 12 randomized controlled trials
ofcalciumordairyintervention(n=2460)andshowedthattherewas
nosignificanteffectontotalbodyBMCintheoverallanalysis[14.How-
ever,asthedatademonstratedstatisticalheterogeneity,furtheranalysis
by pooling the 3 studies in subjects with low calcium intakes of
450–750mg/day demonstrated that calcium or dairy intervention led
toa50g(95%CI24–77g)(1–3%)highertotalbodybonemineralaccre-
tion[14. A few studies also followed up the study participants for a
further 1–3.5years toinvestigate whether theeffects of short-term in-
terventioncouldbemaintainedafterthewithdrawalofthesupplement.
While some studies showed that the effect was maintained[15–17,
others did not[18–20. The reason for the differences infindings
couldbeduetostudyparticipants'habitualcalciumintake,pubertalsta-
tus and theform of intervention.
Most of the calcium or dairy intervention studies were for 2years
orless.Theonlylong-termstudyevaluatedtheeffectsof7-yearcalci-
um supplementation in American girls aged 10.9 years at baseline.
This study showed that calcium supplementation had a significant
positive influence on bone mineral accretion during the pubertal
growth spurt, but the effects were diminished in late adolescence.
This suggested that BMD could catch up during the bone consolida-
tion phase to compensate for the compromised bone mineral accre-
tion during the growth spurt because of inadequate calcium intake.
However, this study also demonstrated that subjects with low calcium
intake may not have complete catch up and thus may not achieve
their target peak bone mass[21.
Insummary,epidemiologicalstudiesshowedthatmilkandcalcium
intake are related to bone mineral accretion during growth, childhood
fracture and bone density at adulthood. Intervention studies showed
positiveeffectsofcalciumanddairyonbonemineralaccretion,particu-
larly in populations withlow habitual calcium consumption. However,
whether these effects could reduce childhood fracture is uncertain,
and whether the effects could be translated into high bone density in
adulthood seems related to subjects' characteristics (habitual calcium
intake, pubertal stage).
Calcium retention in children and adolescents in cross-cultural studies
Thecalciumretentionefficiencyduringgrowthvariesamongethnic
groups. One study comparing American black and white girls showed
that the skeletal calcium retention of black girls was 185mg/d higher
comparedtowhitegirls,andthatblackchildrenhadsignificantlygreat-
er net calcium absorption and lower urinary calcium excretion[22.
Chinesechildrenwithlowhabitualcalciumintakealsohavehighercal-
ciumretentionefficiencycomparedtoCaucasianchildren.Inalongitu-
dinal study of Chinese girls, the calculated apparent calcium retention
efficiency was 41% with average calcium intake of 444mg/day[3,
which is greater than the apparent retention efficiency of 30% at peak
bone mineral accretion in white Canadian girls with average calcium
intakeof1000mg/day[23.AcalciumbalancestudyinChineseadoles-
cents aged 12–17years old with calcium intakes ranging from 352 to
1260mg/day(diet+supplementation)showedthattheapparentcalci-
umabsorption rate was68.7% in boys and 46.4% in girls[24.
Although black children had higher skeletal calcium retention, for
each unit of increase in calcium intake black and white children ab-
sorbandretainthesameamountofcalcium(29).Similarly,a calcium
balance study in Chinese adolescents showed that in girls, calcium
retention increased from 80mg to 355mg per day when calcium in-
take increased from 352mg to 1260mg per day, and in boys calcium
retention increased from 243mg to 646mg per day when calcium
intakeincreasedfrom427mgto1323 mgperday[24].Thesedatato-
getherindicatethatdespite the differencesin habitualcalciumintake
and calcium retention efficiency, within each ethnic group increased
calcium intake is associated with increased bone mineral accretion
up to a threshold level.
Calcium requirement during growth can be defined as the intake
needed to attain the individual's genetically programmed optimal
bone mass. Balance studies of calcium retention in white boys and
girls at different levels of calcium intake (700–2100 mg/day) showed
that calcium retention plateaus at a certain level of intake. The mini-
mum intake to achieve maximal retention has been reported to be
1140 and 1300 mg/day in white boys and girls, respectively[25,26].
Compared to their white counterparts, the calcium intake needed
for achieving maximal calcium retention is significantly lower in
Chinese American girls (970mg/day) and slightly lower in Chinese
boys (1100mg/day)[27]. This could be related to the higher reten-
tion efficiency of Chinese children.

Calcium and bone in young adults
A longitudinal study of Canadian boys and girls followed up to
30 years of age showed that total body BMC reached a plateau at
18 years of age in girls and 20 years in boys[1], indicating that peak
bone mass is achieved around the age of 20. Once peak bone mass
937K. Zhu, R.L. Prince / Clinical Biochemistry 45 (2012) 936–942
is achieved, it is maintained without much change for 10 to 20years.
Few studies have evaluated the association between calcium intake
and bone density in young adults. One study with young Japanese
women and another with 125 young female cross-country runners
showedapositiveassociationbetweencalciumintakeandbonedensity
[28,29. Calciumrequirementinthis periodis 20–30%lower compared
tothefast growingperiod, asbonedevelopmenthas completed.

Calcium and bone in older age
From middle age, the age related bone loss in both male and
femaleisapproximately0.5–1.0%peryear[30].For5–10 yearsduring
and after menopause, women lose bone more rapidly than men, at a
rate of 2–3% per year. This is mostly due to the deficiency of estrogen
at menopause whichleads to decreasedintestinalcalciumabsorption
and renal calcium re-absorption and increased parathyroid hormone
(PTH) secretion and bone resorption[31–37].The effect of calcium in preventing bone loss
A number of randomized controlled trials (RCTs) have examined
the effects of increased calcium intake on bone mineral density as
assessed by dual energy X-ray absorptiometry (DXA). These trials
have shown that in older people with a baseline calcium intake of
500–1000mg/day, increasing the intake by a further 500–1200 mg/day
with or without vitamin D can prevent bone loss, possibly due to the
effect of calcium in suppressing PTH secretion[36,38–41.Inameta-
analysis that included 23 trials of41,419 subjects, calcium or calcium
and vitamin D supplementation was associated with 0.5% reduction in
hip bone loss and 1.2% reduction in spine bone loss[42].Mostofthe
studies on calcium and bone density were conducted in older women
orbothwomenandmen.Thefewstudiesinmenaloneshowedsimilar
effects of calcium supplementation in maintaining bone mass. In a 2-
year RCT in healthy men aged over 40years, the group that received
1200mg calcium per day had 1–1.5% greater increase in spine and hip
BMD compared to the placebo group[43.
Vitamin D may add extra beneficial effects to calcium supplemen-
tation in slowing bone loss. In a 5-year study of older Australian
women,who were randomized to receive either 1200mg/day calcium
alone, 1200mg/day calcium and 1000IU/day vitamin D or placebo,
bonelosswas preventedin both treatmentgroups but not theplacebo
group at year one. However, the effect was only maintained in the
groupthatreceivedbothcalcium and vitamin D at3 and 5years[44.
The effects of calcium in preventing fracture
The majority of randomized controlled trials that investigated
the effects of either calcium supplementation alone or combined cal-
cium and vitamin D supplementation in older people have shown a
reduction in fracture risk, as long as sufficient patient compliance
(75–80%) was achieved[38,45,46]. In a study of 1460 western
Australian women aged 70–85 years at baseline, where study partic-
ipants received either 1200 mg/day calcium or placebo for 5 years,
there was no overall effect in the intention to treat analysis[45].
However, a 30% reduction in any fracture risk was observed in the
per protocol analysis in those taking more than 80% of the tablets

(Fig. 1)
[45]. The trials that failed to show benefit of calcium supple-
mentation on fracture risk reduction mostly had methodological
problems, such as confounding from hormone replacement therapy
administered at the time of study[47], lack of evaluation of patient
compliance[48]or under-powering of the study[47,48]. A meta-
analysis that included 52,625 subjects from 17 trials with fracture as
outcome showed that calcium treatment was associated with a 10%
reduction and calcium in combination with vitamin D was associated
with a 13% reduction in risk of fractures of all types[42]. This meta-
analysis also found that the fracture risk reduction was significantly
greater (24%) in trials in which the compliance rate was high and
the treatment effect was better when the calcium dose≥1200mg,
and the vitamin D dose≥800IU[42].
Elevenofthe17trialswereinwomenonly,andtheother6recruited
both men and women. A subgroup study showed that the treatment
effect was similar in trials of women alone and trials that included both
menandwomen,withariskreductionof12%forboth[42].Thuscalcium
is equally important for fracture prevention in men and women.

Calcium and hip fracture risk
A meta-analysis of pooled cohort studies did not show an associa-
tion between total calcium intake and hip fracture risk in either
women or men[49]. In contrast, two meta-analyses of randomized
controlled trials of calcium monotherapy, {one including four trials
=6504)[49]and the other including three trials (n=5500
women)[50]},suggestedthatcalciumsupplementationwasassociat-
ed with a higher risk of hip fracture. The authors of the second meta-
HR = 0.87, 95% CI 0.67-1.12Intention to treat (n=1460)

Censored for death or lost to follow-up

Calcium Placebo

Compliant patients (n=830)

Censored for death or lost to follow-up

HR = 0.66, 95% CI 0.45-0.97

Calcium

Placebo

1.000.950.90
0.800.00 10.00 20.00 30.00 40.00 50.00 60.00 70.00
0.00 10.00 20.00 30.00 40.00 50.00 60.00 70.00
Proportion without fractureProportion without fracture

Time (months)

Time (months)
Fig. 1.Cox's proportional hazard analysis of the time tofirst incident fracture in 1,460
older Australian women who received 1,200 mg calcium or identical placebo per day
(reproducedfromArchInternMed2006;166:873[45]withpermissionoftheAmerican
Medical Association. Copyright © (2006) American Medical Association. All rights
reserved.).938K. Zhu, R.L. Prince / Clinical Biochemistry 45 (2012) 936–942
analysis hypothesized that the increased risk of hip fracture could
have resulted from suppressed periosteal expansion at the femoral
neck with calcium intervention, as periosteal expansion normally
provides mechanical compensation for bone mineral decline with
ageing[50]. Nevertheless, intervention studies using both calcium
and vitamin D have demonstrated significant reduction in hip frac-
ture risk in older women[46,51]. As older people at high risk of hip
fracturetendtohavebothlowcalciumintakeandvitaminDdeficiency,
it is now widely agreed that calcium should be used in combination
withvitamin D topreventbone lossand fracture.

Meeting calcium requirement
TherecommendedcalciumintakesforUSA[52],Australia[53]and
China[54]are summarized inTable 1. The variation in values may be
due to cross-cultural differences, disparities in expert opinions, and
uncertainty of data in some populations. Generally higher calcium
intake is required during the growing period for the achievement
of maximal peak bone mass, and in women after menopause (over
50 years old) and in men over 70 years old to prevent menopause
and age-related bone loss.
Calcium intake in children and older adults
Low calcium intake is a widespread problem across countries and
age groups.

Children and adolescents
Apopulation-basedsurveyshowedthatthemeancalciumintakeof
adolescent American boys and girls are 1000mg/day and 900mg/day,
respectively[55. However, black children tend to have lower intakes.
A longitudinal study of white and black American girls aged 9 to
18yearsoldusing3-dayfoodrecordshowedthatthemeancalciumin-
take was 825 and 644mg/day for white and black girls, respectively,
with the 50th percentile at 793mg/day for white and 611mg/day for
black girls[56. Calcium intake is even lower in Asian countries. The
2002 China National Nutrition and Health Survey (CNNHS) found that
the daily calcium intakes were 376mg for boys and 343mg for girls
aged 14–17 of years[57. In addition, 70%–80% Chinese boys and girls
of this age group had calcium intakeb50% of the recommended intake
(1000mg/day) and only 3–4%met therecommendedintake[57.

Older people
In America, less than 10% women agedb70 years and less than 1%
women aged >70years meet the calcium requirement through their
diet.Inmen,onlyonein fourhaveadequatecalciumintakefromdiet.In a longitudinal study of free-living older Australian women aged
70–85years, the mean calcium intake ranged from 900 to 980mg/day
andmorethan70%ofthepopulationdidnotachievetheEstimatedAv-
erage Requirement of 1,100mg/day[58. Calcium intake is even lower
in countries where dairy is not a staple food. In China, the 2002 China
National Nutrition and Health Survey (CNNHS) showed that the aver-
age calcium intake was 439mg/day for adults living in urban areas
and 372 for those in rural areas[57; these represent only about half
of therecommended intake of 800–1000mg/day[54.
Intestinal factors affecting intestinal calcium absorption
Milk and dairy products are good sources of calcium. Bonyfish,
legumes, certain nuts and fortified soy milk and breakfast cereals
also contain smaller amounts of calcium. Calcium bioavailability
depends on absorbability and the incorporation of absorbed calcium
into bone. Therefore, both dietary factors influencing intestinal ab-
sorption and the excretion of calcium in urine play a role in calcium
bioavailability[59]. Some food components, such as phytate in bran,
most cereals, seeds and nuts, oxalate in spinach, rhubarb, walnuts
and sorrel, and tannins in tea can form insoluble complexes with
calcium, and thus reduce calcium intestinal absorption. A diet high
in sodium could increase urinary calcium loss and lead to decreased
calcium retention[59].

Lactose
In normal subjects, lactose increases calcium absorption from 22%
to 36%[60]. However, in patients with lactose intolerance, lactose
induces a reduction in calcium absorption by about 5%[60]. This
may be due to the osmotic effects of lactose reducing the effective
concentration of calcium within the bowel[61]. The connection be-
tween lactose intolerance and osteoporotic fracture would appear to
be due to reduced calcium intake associated with avoidance of milk
products[62,63].

Fiber
Highfiber diets have been recommended for various benefits on
thebowelandthecardiovascularsystem.Studiesthathaveexamined
the effects of these diets on calciumconsumption have not found any
significant deleterious effects at moderate consumption offibre con-
taining foods[64]. However, calcium retention is reduced from 25%
to 19% with highfibre intake[65].

Protein
In the past, excessive protein intake had been thought to lead to
chronic metabolic acidosis which causes hypercalciuria and increased

Table 1
Recommended calcium intakes in USA, Australia and China.USA Australia China

Age group

(years)Recommended intake

(mg/day)Age group

(yrs)Recommended intake

(mg/day)Age group

(years)Recommended intake

(mg/day)

1–3EAR 500
RDA 7001–

3EAR 360

RDI 5001-3AI 600

4–8EAR 800
RDA 1,0004–

8EAR 520
RDI 7004–

10AI 800

9-13EAR 1,100

RDA 1,3009-11EAR 800

RDI 1,00011–14AI 1,000

14-18EAR 1,100

RDA 1,30012-18EAR 1,050

RDI 1,30011–17AI 1,000

Men 19–70 and

Women 19-50EAR 800

RDA1,000Men 19–70

and

Women 19-50EAR 840

RDI 1,00018–49AI 800

Men >70and Women >50

EAR 1,000

RDA 1,200Men >70

and Women >50EAR 1,100

RDI 1,300>50AI 1,000
Data source: USA[52], Australia[53]and China[54]. EAR: Estimated average requirement; RDA: Recommended dietary allowances; RDI: Recommended dietary intake;
AI: Adequate intake.939K. Zhu, R.L. Prince / Clinical Biochemistry 45 (2012) 936–942
mineral dissolution[66. However, somerecent data suggest the effect
of protein on calciumbalancecould beneutralasit increases gut calci-
um absorption[67. Furthermore, it has been suggested that adequate
protein intake may benefit the skeleton of older people by providing
amino acids and increasing circulating insulin-like growth factor I
(IGF-I)[68,69. The only long term dietary protein intervention study
was a 2-year randomized controlled trial with 219 healthy ambulant
women aged 70–80years. Participants were randomized to either a
high protein drink containing 30g of whey protein or an isocaloric
placebo drink containing 2.1g protein (n=110). At 2years, the high-
protein group had a marginally higher urinary calcium excretion and
significantly higher IGF-I levels compared to the placebo group, but
there was no significant difference between the two groups in change
in bone mass or strength. This study showed that in protein-replete
healthyambulant women,30g ofextraproteindidnothave beneficial
or deleterious effectsonbone massorstrength[70.

Achlorhydria
It has been shown that in achlorhydric individuals the absorption
of calcium when administered as calcium carbonate is less than when
administeredascalciumcitrate.Thisdifferentialabsorptionisabolished
if thecalciumis takenwithfood[71.Intermsofpreventingboneloss,
calcium lactate gluconate has identical effects to milk powder that
containsthe sameamount of calcium[36,72.

Calcium supplementation
Althoughobtainingsufficientcalciumfromdietispreferred,supple-
mentationisneededwhenadequatecalciumintakecannotbeachieved
withdiet.Arecentexpertpanelreporthassuggestedthatsupplementa-
tion with calcium and vitamin D should be recommended in womenwith osteoporosis, or at increased risk of osteoporosis i.e. aged over
65years, BMD T-score lessthan−1,or provencalciumand/or vitamin
D insufficiency[73. The expert panel recommended that women at
increased fracture risk should receive both calcium and vitamin D
supplements, including 1000–1200mg calcium (depending on dietary
calcium intake) and 800IUvitamin D daily[73. It is recommended by
the Institute of Medicine that the total calcium intake from diet and
supplementation should not exceed the tolerable upper intake limit
(UL) of 3,000mg/day for children and adolescents aged 9–18years,
2,500mg/day for 19–50year olds and 2,000mg/day for those aged>
50years[52.
Calcium from supplements is absorbed more efficiently when
taken in doses less than 500mg[74]. In the fasting state, calcium is
betterabsorbedfromcalciumcitratethancalciumcarbonate,andcal-
cium as carbonate is better absorbed when taken with food. Never-
theless, the Institute of Medicine has recommended taking calcium
supplementation with foods to reduce the risk of developing kidney
stone[52]. In addition, 500mg calcium as citrate has been reported
to have the equivalent effects of 1000 mg calcium as carbonate in
suppressing parathyroid hormone and bone resorption; thus using
calcium citrate supplement may be associated with fewer adverse
effects and better long-term compliance[75].
Controversiesoncalciumsupplementationandvasculardiseaserisk
Recently,asecondaryanalysisofacalciumsupplementationstudy

inolderNewZealandwomen

[76]anda meta-analysisincluded8016
men and women fromfive prospective calcium intervention studies
[77]have raised the concern that calcium supplementation may
increase the risk of myocardial infarction. A further meta-analysis in-
cluded trial level data from 28,072 participants from nine studies
using either calcium supplement alone or both calcium and vitamin
D[78]. This meta-analysis concluded that supplementation with
calcium alone or both calcium and vitamin D increased the risk of
myocardial infarction by 24%andthe composite ofmyocardialinfarc-
tion or stroke by 15%[78]. However, carefully reviewing these three
reports, we could see that the conclusions are dependent on studies
which have compared multiple endpoints, conducted in heteroge-
nous populations, and most of the time used less than ideal methods
ofascertainmentforvasculardiseases.Arecentreportshowedthatin
seven RCTs of calcium intervention, selffireported gastrointestinal
adverse event rates were more common in participants receiving
calcium and there was a higher error rate in the self-report of myo-
cardial infarction in the calcium group[79]. The authors suggested
that the higher error rate in the self-report of myocardial infarction
inthecalciumgroupcouldbeduetoincreasedfunctionalgastrointes-
tinaldisordersassociatedwithcalciumsupplementationmistakenfor
myocardial infarction[79]. It is also interesting to note that in the
Women's Health Initiative (WHI), participants who were taking per-
sonal calcium supplements at randomisation, addition of calcium
and vitamin D did not increase cardiovascular disease risk[78].
In contrast, in a study that used a more accurate method of vascu-
lar disease ascertainment, no association of calcium intervention and
atherosclerotic vascular disease risk was found[45]. In this trial 1460
women aged 75.1±2.7years at baseline participated in a 5-year,
randomised,double-blind,placebo-controlledtrialofcalciumcarbon-
ate (1200mg/day calcium or placebo) and were further followed up
for an additional 4.5years[45]. Complete verified atherosclerotic
vascular hospitalization and mortality data were obtained using the
Western Australia Data Linkage System hospitalization and mortality
record. The calcium group did not have a higher risk of death orfirst-
time hospitalisation from atherosclerotic vascular disease in either
the 5-year RCT (multivariate-adjusted HR 0.938 95% CI 0.690-1.275)
or during the 9.5years of observational study (multivariate-adjusted
HR 0.919 95% CI 0.737–1.146) (Fig. 2)[80]. Thus, this trial using a
more accurate method of vascular disease ascertainment provides

0.0

Hazard Ratio

All Participants

HR 0.938 (95%CI 0.690-1.275)

Previous Diabetes

HR 0.459 (95% CI 0.181-1.166)

Previous ASVD

HR 0.438 (95% CI 0.246-0.781)

Vascular Medications

HR 0.914 (95% CI 0.647-1.292)

Smoking

HR 1.360 (95% CI 0.849-2.177)

eGFR

HR 0.975 (95% CI 0.654-1.454)

0.51.01.52.02.53.0

Hazard Ratio

All Participants

HR 0.919 (95%CI 0.737-1.146)

Previous Diabetes

HR 0.551 (95% CI 0.254-1.196)

Previous ASVD

HR 0.669 (95% CI 0.423-1.059)

Vascular Medications

HR 0.931 (95% CI 0.720-1.204)

Smoking

HR 1.062 (95% CI 0.752-1.499)

eGFR

HR 1.015 (95% CI 0.751-1.373)

0.00.51.01.52.02.53.0

9.5 years5 years
Fig. 2.The effect of calcium treatment compared with placebo on all atherosclerotic
vascular disease hospitalisations and mortality outcomes over 5 and 9.5 years. The
analyses utilized groups with the named baseline risk factor. Analyses adjusted for
baseline age, calcium intake, compliance, cardiovascular disease, eGFR, diabetes, previ-
ous or current smoking and baseline cardiovascular medications unless that covariate
was the subject of the analysis. eGFR refers to estimated glomerular function rate
while ASVD refers to atherosclerotic vascular disease. (Reproduced from J Bone
Miner Res. 2011;26: Page 39[80]with permission of the American Society for Bone
and Mineral Research).940K. Zhu, R.L. Prince / Clinical Biochemistry 45 (2012) 936–942
compelling evidence that calcium supplementation of 1200 mg daily
does not significantly increase the risk of atherosclerotic vascular
disease in elderly women.

Conclusions
Osteoporosis and related fractures are important public health
problems world-wide. Calcium intake influences peak bone mass
achieved in early adulthood by influencing skeletal calcium retention
during bone growth and plays a role in preventing bone loss and os-
teoporotic fractures in later life. Low calcium intake is a widespread
problem across countries and age groups. Therefore, ensuring ade-
quatecalciumintakethroughoutlifetimeisimportantforbonehealth
and the prevention osteoporosis and related fractures.

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942K. Zhu, R.L. Prince / Clinical Biochemistry 45 (2012) 936–942

Review

Calcium and bone

Kun Zhu⁎, Richard L. Prince
Department of Endocrinology and Diabetes, Sir Charles Gairdner Hospital, Perth, WA, Australia
School of Medicine and Pharmacology, University of Western Australia, Perth, WA, Australia

abstractarticle info
Article history:

Received 23 December 2011

Received in revised form 4 May 2012

Accepted 8 May 2012
Available online 17 May 2012Keywords:Calcium intakeCalcium supplementationBone mineral densityPeak bone massFracture

Children

Adolescents

Older people
Objective:Evaluate the role of calcium on bone health.
Methods:Review of literatures on calcium and bone development during childhood and bone health in
adulthood and older age.
Results:Calcium intake in⁎uences skeletal calcium retention during growth and thus affects peak bone
mass achieved in early adulthood. Increased calcium intake is associated with increased bone mineral accre-
tion rate up to a threshold level in all ethnic groups. The minimum intake to achieve maximal retention is
1140 mg/day for white boys and 1300 mg/day for white girls. Calcium also plays a role in preventing bone
loss and osteoporotic fractures in later life. Meta-analyses report that calcium supplementation reduce
bone loss by 0.5–1.2% and the risk of fracture of all types by at least 10% in older people. Low calcium intake
is a widespread problem across countries and age groups.
Conclusion:Adequatecalciumintakethroughoutlifetimeisimportantforbonehealthandthepreventionof
osteoporosis and related fractures.
© 2012 The Canadian Society of Clinical Chemists. Published by Elsevier Inc. All rights reserved.

Contents
Introduction................................................................ 937
Calcium and bone development during childhood and adolescence....................................... 937
Calcium and dairy intake and bone mineral accretion........................................... 937
Calcium retention in children and adolescents in cross-cultural studies................................... 937
Calcium and bone in young adults...................................................... 937
Calcium and bone in older age........................................................ 938
The effect of calcium in preventing bone loss............................................... 938
The effects of calcium in preventing fracture............................................... 938
Calcium and hip fracture risk...................................................... 938
Meeting calcium requirement........................................................ 939
Calcium intake in children and older adults................................................ 939
Children and adolescents..................................................... 939
Older people........................................................... 939
Intestinal factors affecting intestinal calcium absorption.......................................... 939
Lactose............................................................. 939
Fiber.............................................................. 939
Protein............................................................. 939
Achlorhydria........................................................... 940
Calcium supplementation........................................................ 940
Controversiesoncalciumsupplementationandvasculardiseaserisk....................................... 940
Conclusions................................................................. 941
References................................................................. 941Clinical Biochemistry 45 (2012) 936–942
⁎Corresponding author at: Department of Endocrinology and Diabetes, Sir Charles Gairdner Hospital, Nedlands, WA 6009, Australia. Fax: +61 8 9346 1317.
E-mail addresses:kun.zhu@uwa.edu.au(K. Zhu),richard.prince@uwa.edu.au(R.L. Prince).
0009-9120/$–see front matter © 2012 The Canadian Society of Clinical Chemists. Published by Elsevier Inc. All rights reserved.
doi:10.1016/j.clinbiochem.2012.05.006Contents lists available atSciVerse ScienceDirect

Clinical Biochemistry
journal homepage: www.elsevier.com/locate/clinbiochem

Introduction
The adult human body contains around 1kg calcium on average,
more than 99% of which exists in bone and teeth. In bone, calcium
exists in mineral form as hydroxyapatite [Ca

(PO

(OH)

Calcium

infl
uences bone strength through its effect on bone mass. Calcium
intake is one of the important modifiable environmental factors for
thenormaldevelopmentoftheskeletonduringgrowthandthemain-
tenance of bone mass in later life.
Calciumandbonedevelopmentduringchildhoodandadolescence
Calcium and dairy intake and bone mineral accretion
Bone mineral accretion during growth is a major determinant of
peak bone mass, which is associatedwith the risk of developing oste-
oporosis in older age. The peri-pubertal and pubertal years are a
critical period for bone mineral accretion, with around 39% of young
adult total body bone mineral gained in the 4years surrounding
peak height velocity[1]. Many factors, including genetics, gender,
endocrine and nutritional factors influence the attainment of peak
bone mass. Most epidemiologic and randomised studies of calcium
intake have been undertaken in subjects with diets adequate in other
nutrients such asprotein, carbohydrate and fat.
Calcium intake influences skeletal calcium retention during bone
growth and thus plays a role in peak bone mass achieved in early
adulthood. Longitudinal studies in Canadian boys[2]and Chinese
girls[3]have shown that calcium intake was a minor but significant
predictor of total body bone mass. Inadequate calcium intake during
growing period could compromise peak bone mass attained at skele-
tal maturityand thuspredisposeindividualsto increased risk of oste-
oporotic fracture in later life. A study of 3251 Caucasian women from
thethirdAmericanNationalHealthandNutritionExaminationsurvey
showedthatwomenwithlowmilkintakeduringchildhoodandadoles-
cencehadlowbonedensityinadulthoodandgreaterriskoffracture[4.
Inaddition,lowbonemassmayalsocontributetochildhoodfracture.A
report in New Zealand children showed that those who avoided cow's
milkhad 1.7 times higher riskforpre-pubertalfracture[5.
The majority of intervention studies with dairy foods or calcium
supplement in children and adolescents from different ethnic back-
grounds have shown positive effects on bone mineral accretion at
one or more of the sites measured[6–

12]. Two meta-analyses evalu-
atedtheeffectsofcalciumsupplementationonbonemassinchildren.
Thefirstmeta-analysis whichincluded19 studies(n=2859)showed
that calcium supplementation had a significant effect on total body
bone mineral content (BMC) (standardised mean difference 0.14, 95%
CI 0.01–0.27) and forearm bone mineral density (BMD) (0.14, 95% CI
0.04–0.24), but no effect on BMD at the femoral neck or lumbar spine
[13. The other meta-analysis included 12 randomized controlled trials
ofcalciumordairyintervention(n=2460)andshowedthattherewas
nosignificanteffectontotalbodyBMCintheoverallanalysis[14.How-
ever,asthedatademonstratedstatisticalheterogeneity,furtheranalysis
by pooling the 3 studies in subjects with low calcium intakes of
450–750mg/day demonstrated that calcium or dairy intervention led
toa50g(95%CI24–77g)(1–3%)highertotalbodybonemineralaccre-
tion[14. A few studies also followed up the study participants for a
further 1–3.5years toinvestigate whether theeffects of short-term in-
terventioncouldbemaintainedafterthewithdrawalofthesupplement.
While some studies showed that the effect was maintained[15–17,
others did not[18–20. The reason for the differences infindings
couldbeduetostudyparticipants'habitualcalciumintake,pubertalsta-
tus and theform of intervention.
Most of the calcium or dairy intervention studies were for 2years
orless.Theonlylong-termstudyevaluatedtheeffectsof7-yearcalci-
um supplementation in American girls aged 10.9 years at baseline.
This study showed that calcium supplementation had a significant
positive influence on bone mineral accretion during the pubertal
growth spurt, but the effects were diminished in late adolescence.
This suggested that BMD could catch up during the bone consolida-
tion phase to compensate for the compromised bone mineral accre-
tion during the growth spurt because of inadequate calcium intake.
However, this study also demonstrated that subjects with low calcium
intake may not have complete catch up and thus may not achieve
their target peak bone mass[21.
Insummary,epidemiologicalstudiesshowedthatmilkandcalcium
intake are related to bone mineral accretion during growth, childhood
fracture and bone density at adulthood. Intervention studies showed
positiveeffectsofcalciumanddairyonbonemineralaccretion,particu-
larly in populations withlow habitual calcium consumption. However,
whether these effects could reduce childhood fracture is uncertain,
and whether the effects could be translated into high bone density in
adulthood seems related to subjects' characteristics (habitual calcium
intake, pubertal stage).
Calcium retention in children and adolescents in cross-cultural studies
Thecalciumretentionefficiencyduringgrowthvariesamongethnic
groups. One study comparing American black and white girls showed
that the skeletal calcium retention of black girls was 185mg/d higher
comparedtowhitegirls,andthatblackchildrenhadsignificantlygreat-
er net calcium absorption and lower urinary calcium excretion[22.
Chinesechildrenwithlowhabitualcalciumintakealsohavehighercal-
ciumretentionefficiencycomparedtoCaucasianchildren.Inalongitu-
dinal study of Chinese girls, the calculated apparent calcium retention
efficiency was 41% with average calcium intake of 444mg/day[3,
which is greater than the apparent retention efficiency of 30% at peak
bone mineral accretion in white Canadian girls with average calcium
intakeof1000mg/day[23.AcalciumbalancestudyinChineseadoles-
cents aged 12–17years old with calcium intakes ranging from 352 to
1260mg/day(diet+supplementation)showedthattheapparentcalci-
umabsorption rate was68.7% in boys and 46.4% in girls[24.
Although black children had higher skeletal calcium retention, for
each unit of increase in calcium intake black and white children ab-
sorbandretainthesameamountofcalcium(29).Similarly,a calcium
balance study in Chinese adolescents showed that in girls, calcium
retention increased from 80mg to 355mg per day when calcium in-
take increased from 352mg to 1260mg per day, and in boys calcium
retention increased from 243mg to 646mg per day when calcium
intakeincreasedfrom427mgto1323 mgperday[24].Thesedatato-
getherindicatethatdespite the differencesin habitualcalciumintake
and calcium retention efficiency, within each ethnic group increased
calcium intake is associated with increased bone mineral accretion
up to a threshold level.
Calcium requirement during growth can be defined as the intake
needed to attain the individual's genetically programmed optimal
bone mass. Balance studies of calcium retention in white boys and
girls at different levels of calcium intake (700–2100 mg/day) showed
that calcium retention plateaus at a certain level of intake. The mini-
mum intake to achieve maximal retention has been reported to be
1140 and 1300 mg/day in white boys and girls, respectively[25,26].
Compared to their white counterparts, the calcium intake needed
for achieving maximal calcium retention is significantly lower in
Chinese American girls (970mg/day) and slightly lower in Chinese
boys (1100mg/day)[27]. This could be related to the higher reten-
tion efficiency of Chinese children.

Calcium and bone in young adults
A longitudinal study of Canadian boys and girls followed up to
30 years of age showed that total body BMC reached a plateau at
18 years of age in girls and 20 years in boys[1], indicating that peak
bone mass is achieved around the age of 20. Once peak bone mass
937K. Zhu, R.L. Prince / Clinical Biochemistry 45 (2012) 936–942
is achieved, it is maintained without much change for 10 to 20years.
Few studies have evaluated the association between calcium intake
and bone density in young adults. One study with young Japanese
women and another with 125 young female cross-country runners
showedapositiveassociationbetweencalciumintakeandbonedensity
[28,29. Calciumrequirementinthis periodis 20–30%lower compared
tothefast growingperiod, asbonedevelopmenthas completed.

Calcium and bone in older age
From middle age, the age related bone loss in both male and
femaleisapproximately0.5–1.0%peryear[30].For5–10 yearsduring
and after menopause, women lose bone more rapidly than men, at a
rate of 2–3% per year. This is mostly due to the deficiency of estrogen
at menopause whichleads to decreasedintestinalcalciumabsorption
and renal calcium re-absorption and increased parathyroid hormone
(PTH) secretion and bone resorption[31–37].The effect of calcium in preventing bone loss
A number of randomized controlled trials (RCTs) have examined
the effects of increased calcium intake on bone mineral density as
assessed by dual energy X-ray absorptiometry (DXA). These trials
have shown that in older people with a baseline calcium intake of
500–1000mg/day, increasing the intake by a further 500–1200 mg/day
with or without vitamin D can prevent bone loss, possibly due to the
effect of calcium in suppressing PTH secretion[36,38–41.Inameta-
analysis that included 23 trials of41,419 subjects, calcium or calcium
and vitamin D supplementation was associated with 0.5% reduction in
hip bone loss and 1.2% reduction in spine bone loss[42].Mostofthe
studies on calcium and bone density were conducted in older women
orbothwomenandmen.Thefewstudiesinmenaloneshowedsimilar
effects of calcium supplementation in maintaining bone mass. In a 2-
year RCT in healthy men aged over 40years, the group that received
1200mg calcium per day had 1–1.5% greater increase in spine and hip
BMD compared to the placebo group[43.
Vitamin D may add extra beneficial effects to calcium supplemen-
tation in slowing bone loss. In a 5-year study of older Australian
women,who were randomized to receive either 1200mg/day calcium
alone, 1200mg/day calcium and 1000IU/day vitamin D or placebo,
bonelosswas preventedin both treatmentgroups but not theplacebo
group at year one. However, the effect was only maintained in the
groupthatreceivedbothcalcium and vitamin D at3 and 5years[44.
The effects of calcium in preventing fracture
The majority of randomized controlled trials that investigated
the effects of either calcium supplementation alone or combined cal-
cium and vitamin D supplementation in older people have shown a
reduction in fracture risk, as long as sufficient patient compliance
(75–80%) was achieved[38,45,46]. In a study of 1460 western
Australian women aged 70–85 years at baseline, where study partic-
ipants received either 1200 mg/day calcium or placebo for 5 years,
there was no overall effect in the intention to treat analysis[45].
However, a 30% reduction in any fracture risk was observed in the
per protocol analysis in those taking more than 80% of the tablets

(Fig. 1)
[45]. The trials that failed to show benefit of calcium supple-
mentation on fracture risk reduction mostly had methodological
problems, such as confounding from hormone replacement therapy
administered at the time of study[47], lack of evaluation of patient
compliance[48]or under-powering of the study[47,48]. A meta-
analysis that included 52,625 subjects from 17 trials with fracture as
outcome showed that calcium treatment was associated with a 10%
reduction and calcium in combination with vitamin D was associated
with a 13% reduction in risk of fractures of all types[42]. This meta-
analysis also found that the fracture risk reduction was significantly
greater (24%) in trials in which the compliance rate was high and
the treatment effect was better when the calcium dose≥1200mg,
and the vitamin D dose≥800IU[42].
Elevenofthe17trialswereinwomenonly,andtheother6recruited
both men and women. A subgroup study showed that the treatment
effect was similar in trials of women alone and trials that included both
menandwomen,withariskreductionof12%forboth[42].Thuscalcium
is equally important for fracture prevention in men and women.

Calcium and hip fracture risk
A meta-analysis of pooled cohort studies did not show an associa-
tion between total calcium intake and hip fracture risk in either
women or men[49]. In contrast, two meta-analyses of randomized
controlled trials of calcium monotherapy, {one including four trials
=6504)[49]and the other including three trials (n=5500
women)[50]},suggestedthatcalciumsupplementationwasassociat-
ed with a higher risk of hip fracture. The authors of the second meta-
HR = 0.87, 95% CI 0.67-1.12Intention to treat (n=1460)

Censored for death or lost to follow-up

Calcium Placebo

Compliant patients (n=830)

Censored for death or lost to follow-up

HR = 0.66, 95% CI 0.45-0.97

Calcium

Placebo

1.000.950.90
0.800.00 10.00 20.00 30.00 40.00 50.00 60.00 70.00
0.00 10.00 20.00 30.00 40.00 50.00 60.00 70.00
Proportion without fractureProportion without fracture

Time (months)

Time (months)
Fig. 1.Cox's proportional hazard analysis of the time tofirst incident fracture in 1,460
older Australian women who received 1,200 mg calcium or identical placebo per day
(reproducedfromArchInternMed2006;166:873[45]withpermissionoftheAmerican
Medical Association. Copyright © (2006) American Medical Association. All rights
reserved.).938K. Zhu, R.L. Prince / Clinical Biochemistry 45 (2012) 936–942


2012 Zhu, Calcium a bone

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