Speaking of Supplements... calcium

[Guest guest]

D. Wark, Professor of Medicine, Department of Medicine, The

University of Melbourne, and Bone and Mineral Service, The Royal

Melbourne Hospital; and Caryl Nowson, Associate Professor, School of

Health Sciences, Deakin University, Melbourne

Calcium supplementation: the bare bones

SYNOPSIS

An adequate calcium intake is an essential part of the prevention

and treatment of osteoporosis. Two to three serves of calcium-rich

foods each day provides sufficient calcium for most non-pregnant

adults. If this target is not achievable, calcium supplementation is

generally effective, cheap and safe for most people. Calcium

carbonate (without vitamin and mineral additives) is the preferred

supplement in most cases. Problems with calcium absorption arise due

to factors including high-fibre vegetarian diets, achlorhydria, long-

term glucocorticoid therapy and vitamin D deficiency. Vitamin D

deficiency is extremely common in some ethnic groups and the elderly

who are housebound or in residential care. These at-risk groups

generally require vitamin D supplementation to achieve adequate

intestinal absorption of calcium.

Index words: osteoporosis, diet, vitamin D.

(Aust Prescr 2003;26:126-7)

Introduction

There is strong evidence that an adequate calcium intake is

important for healthy bones, and as part of the preventive strategy

in individuals at high risk for osteoporosis (for example, patients

receiving long-term glucocorticoid therapy). It is also an

adjunctive treatment in patients with osteoporosis.1 An adequate

calcium intake (and vitamin D status) was a prerequisite for the

clinical trials assessing the anti-fracture efficacy of all of the

currently available medications for treating osteoporosis, with the

exception of calcitriol. Patients being treated for osteoporosis

should therefore always have an adequate intake of calcium, and a

normal vitamin D status.

Dietary calcium

For most people, calcium requirements are in the range 800-1500 mg

daily. These requirements are best met by consuming at least two or

three servings of high calcium foods daily (for example, milk

products, calcium-fortified soy products). A serving of dairy food

contains 200-300 mg of elemental calcium.2 (When checking the true

calcium content of foods and supplements, it is the elemental

calcium that matters.) Daily physiological needs may be at least

1000 mg during growth, in pregnancy and possibly in the late

postmenopausal stage of life. Recommended dietary intakes of calcium

(under review) indicate an additional 300 mg daily in pregnancy and

an additional 400 mg daily for lactation.

Currently, approximately 60% of dietary calcium comes from dairy

foods2 (although this proportion may fall with the introduction of

more calcium-fortified foods). People who avoid dairy products

usually have an inadequate dietary calcium intake. Where necessary,

calcium intake should be boosted by increasing the intake of high

calcium foods such as dairy products and calcium-fortified soy

products if possible. These products also contain a range of other

essential nutrients including protein, phosphorus, magnesium and

some vitamins which are of particular importance during growth,

pregnancy and ageing.

Calcium supplements: how much, which type, how taken?

Calcium supplements are a very useful way of helping individuals who

are unable to consume sufficient calcium from dietary sources. An

extra 500-700 mg elemental calcium per day will suffice for most

people. The cheapest, easiest way to achieve this objective is with

a single calcium carbonate tablet containing 600 mg elemental

calcium.

Calcium carbonate contains 40% elemental calcium by weight compared

with 21% in calcium citrate. Although calcium citrate is more

soluble and its bioavailability may be approximately 25% greater

than that of calcium carbonate3 it is also more expensive. Calcium

citrate was found to be less cost-effective than a calcium carbonate

preparation in a recent study.4 Clinical situations where calcium

citrate may be preferred over calcium carbonate include achlorhydria

(calcium carbonate requires an acid environment to dissolve, calcium

citrate does not), and in patients who need calcium supplements but

have a history of kidney stones (citrate in the urine inhibits

calcium oxalate precipitation).5 Calcium phosphate preparations have

not been studied extensively, but appear to be absorbed adequately.6

In general, it is recommended to prescribe or advise the use of

widely available, major brand-name calcium preparations whose

absorbability has been well documented. This is because the

absorbability of some marketed products is only 40-60% of that of

plain calcium carbonate.

Administration

It is generally not important when calcium supplements are taken in

relation to meals. Patients with achlorhydria appear to be an

exception. Calcium carbonate is very poorly absorbed in these

patients when fasting, but is absorbed satisfactorily when ingested

with a meal.5 There is some evidence that taking calcium supplements

in the evening may be advantageous, by suppressing the nocturnal

rise in bone resorption. It is critical that calcium and oral

bisphosphonates are taken at least several hours apart as calcium

binds with these medications and prevents their absorption.

Factors that impair the absorption of calcium supplements

Some dietary constituents can impair calcium bioavailability by

forming insoluble calcium complexes.7 These substances include

phytates (found in cereals, bran, soybeans, seeds) and oxalates

(found in spinach, rhubarb, walnuts). Some vegetarian diets may

therefore adversely affect calcium balance, particularly if the

calcium content is low due to the avoidance of dairy products.

Inadequate vitamin D nutrition is associated with impaired

intestinal calcium absorption and must be corrected for ingested

calcium to be effective. As the vitamin D content of our diet is

generally low, people with low levels of sunlight exposure (the

chronically-ill, housebound, people in residential care, some ethnic

groups) are at high risk for vitamin D deficiency. Dark-skinned

people, especially veiled women, are an important risk group. Their

vitamin D status in pregnancy is a particular concern. Daily needs

are probably of the order of 800 IU in these high-risk groups. This

can be given as oral vitamin D2 1000 IU daily.

Long-term glucocorticoid treatment also causes calcium

malabsorption. In general, when calcium supplements are recommended,

vitamin D nutritional adequacy should be assured and other bone-

protective interventions may be indicated. Renal impairment is

associated with calcium malabsorption and this aspect of the care of

patients with renal disease requires specialist advice. Achlorhydria

reduces the absorption of calcium carbonate. In theory, proton pump

inhibitors might impair calcium absorption, but evidence is lacking.

It may be preferable for patients taking proton pump inhibitors to

take calcium supplements with meals and perhaps to take calcium in

the form of calcium citrate.

Adverse effects

Calcium supplements are usually well tolerated. Occasional adverse

effects include constipation, bloating and flatulence. Changing

preparations (for example, from calcium carbonate to calcium

citrate) may alleviate these adverse effects. Calcium

supplementation is contraindicated in the presence of hypercalcaemia

or marked hypercalciuria, and during calcitriol therapy for

osteoporosis, because of the risk of inducing hypercalcaemia or

hypercalciuria. Measurement of the serum calcium, albumin and

creatinine should therefore be part of the pre-treatment evaluation

of patients presenting with apparent osteoporosis. Caution is also

required in renal impairment, sarcoidosis and when there is a

history of nephrolithiasis.

What about the additives?

Evidence is lacking that the small amounts of various mineral and

vitamin additives present in some marketed calcium supplements

improve the effectiveness of the supplements. In theory, the

addition of vitamin D might be beneficial, but the amount of vitamin

D added (100–200 IU) is insufficient to prevent vitamin D deficiency

in someone at risk. An adequate vitamin D supplement of 1000 IU is

therefore recommended for these individuals.

Conclusion

There is a strong case in favour of calcium supplementation when an

adequate dietary calcium intake cannot be achieved. In most non-

pregnant adults, a daily supplement of 600 mg elemental calcium as

calcium carbonate is sufficient, though occasionally more may be

required. Coexisting vitamin D deficiency is common, particularly in

the elderly in residential care, and also needs to be corrected.

R E F E R E N C E S

1. Heaney RP. Calcium, dairy products and osteoporosis [review]. J

Am Coll Nutr 2000;19:83S-99S.

2. Angus RM, Eisman JA. Osteoporosis: the role of calcium intake and

supplementation. Med J Aust 1988;148:630-3.

3. Sakhaee K, Bhuket T, -Huet B, Rao DS. Meta-analysis of

calcium bioavailability: a comparison of calcium citrate with

calcium carbonate. Am J Ther 1999;6:313-21.

4. Heaney RP, Dowell SD, Bierman J, Hale CA, Bendich A.

Absorbability and cost effectiveness in calcium supplementation. J

Am Coll Nutr 2001;20:239-46.

5. Levenson DI, Bockman RS. A review of calcium preparations

[published erratum appears in Nutr Rev 1994;52:364]. Nutr Rev

1994;52:221-32.

6. Shires R, Kessler GM. The absorption of tricalcium phosphate and

its acute metabolic effects. Calcif Tissue Int 1990;47:142-4.

7. Gueguen L, Pointillart A. The bioavailability of dietary calcium

[review]. J Am Coll Nutr 2000;19:119S-136S.

Conflict of interest: none declared

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