They’re touted as an insurance policy against osteoporosis, but which offers the best payoff?
almost learn it at our mother’s knee: calcium is good for our bones and
teeth, and we must drink lots of milk to give us enough calcium to grow
up to be strong, healthy adults. For years, this health message has
been an article of faith. However, recent evidence is beginning to
challenge the value of milk - certainly in later life (see box, p 2).
is the most common mineral in the human body - 99 per cent of it is in
the bones and teeth, where it plays a structural role. The remaining 1
per cent is in body tissues and fluids, where it is essential for cell
metabolism, blood-clotting, muscle contraction and nerve-impulse
However, the amount of calcium in the bones is not
fixed. There is a continuous exchange of calcium between the bones and
the bloodstream to maintain adequate levels in each. This process is
controlled by hormones. Vitamin D and magnesium are also involved as
they help calcium in the blood become reabsorbed into the bones.
and large, the body regulates its own calcium levels, maintaining
homoeostasis (a normal, balanced state) by compensating for any excess
or shortage by changing calcium absorption rates.
lost from the body in the usual processes of waste elimination; much
more is lost during breastfeeding. Natural sources of calcium are dairy
products, eggs, nuts, seeds, dried fruit and leafy vegetables.
recommendations for an ideal daily calcium intake have been somewhat
volatile in recent years as opinions change about calcium’s importance.
In fact, a recent scientific review all but described the current
Recommended Daily Allowance guidelines as a mess, complaining of 'the
lack of quantitative data on which to base estimates of average calcium
requirements' (Calcif Tissue Int, 2002; 70: 83-8).
standard adult RDA was 700 mg a day until 1997, when the US National
Academy of Sciences Institute of Medicine substantially increased it to
1200 mg. They also recommended 200-500 mg a day for young children,
rising to about 1300 mg for adolescents and those over 50. The dose is
even higher for breastfeeding and adolescent mothers.
daily intakes of calcium from foods are in the 500-800 mg range so, if
the latest Dietary Reference Intakes are to be believed, a normal adult
diet will not provide enough calcium.
therefore, appear to be necessary. However, here again, there is
confusion as to how much calcium to advise people to take. The reason
for this is apparently because the basic experimental science simply
hasn’t been adequately done (J Int Med Res, 1999; 27: 1-14).
picture becomes even more complicated when assessing the evidence for
the benefits of calcium. Least controversial are the claims that low
calcium is associated with colon cancer, high blood pressure and
premenstrual syndrome (Am J Obstet Gynecol, 1999; 181: 1560-9).
cancer, in particular, has been shown to be less common in people with
high calcium intakes. This has been recently confirmed experimentally.
People at high risk of colon cancer were given a daily dose of 900 mg
of calcium carbonate, which was found to significantly reduce the
incidence of cancerous polyps in the intestinal tract (Nutr Cancer,
2001; 41: 150-5).
Also non-controversial is the relationship
between calcium intake and dental health - in both childhood and old
age. A recent placebo-controlled study showed that old people lost
fewer teeth while taking a daily 1000-mg calcium supplement for three
years, a benefit that persisted even after the supplements were stopped
(Am J Med, 2001; 111: 452-6).
Calcium’s major role, however, is not in teeth, but in the bones, and this is where the evidence becomes complicated.
major medical problem involving the skeleton is the condition called
osteoporosis, popularly known as ‘brittle bone disease’. It causes the
vast majority of bone fractures in the elderly. It’s not easy to
diagnose; typically, the first sign of it will be a fracture after a
fall which a younger adult would take in his stride.
fractures often occur just above the wrist and at the top of the thigh
bone. In more advanced cases, the spinal vertebrae may crumble, causing
both pain due to compression of the spinal nerves and a progressive
loss of height.
Healthy bone consists of a hard outer shell
with softer, spongy bone cells underneath. Its principal components are
collagen, a protein that gives bones their elasticity, and calcium,
which provides their hardness and strength.
mainly caused by the loss of collagen which also takes away calcium
from both spongy and hard bone, causing it to become less dense and
more brittle. Bone size, though, is not affected.
of bone density seems to be an inevitable part of the ageing process.
Both men and women start losing bone density from age 30 but, over the
years, women become much worse off than men. By age 70, women on
average lose 25 per cent of their bone density whereas men only lose
It is thought that women are more severely affected
because of a progressive loss of oestrogen, particularly after the
menopause. One indication that oestrogen is the culprit is that bone
loss accelerates if the ovaries no longer function, for example, after
a hysterectomy. However, the fact that not all postmenopausal women
develop osteoporosis suggests that oestrogen loss is not the only
factor (Am J Obstet Gynecol, 1987; 156: 1342-6).
appears to have reached pandemic proportions, affecting one in three
women and one in 12 men, making it one of the West’s most common
diseases. In Europe, it’s estimated to cause nearly 400,000 hip
fractures a year (Publ Health Nutr, 2001; 4: 547-59).
result, taking calcium supplements has skyrocketed - particularly among
women. A recent US survey discovered that nearly 70 per cent of elderly
women now supplement with calcium to avoid osteoporosis (Osteoporos
Int, 2002; 13: 657-62). Calcium supplement sales are described as ‘big
business’, with more than a sevenfold increase in the early 1980s,
representing then a $130 million business (Am Diet Assoc, 1989; 89:
Money well spent?
It seems axiomatic that the more
calcium in the diet, the more calcium in the bones and, by the same
token, the more calcium in the bones, the stronger the bones and the
less risk of osteoporosis. The logic appears unassailable and, until
recently, was almost a universally acknowledged conclusion.
hard evidence has been hard to come by. A recent US survey of
middle-aged Mexican women found no association between dietary calcium
and bone strength, measured by bone mineral density (BMD) (Osteoporos
Int, 1997; 7: 533-8). Adolescent girls were also assessed by calcium
intake, but again with no correlation to their BMD - not even with
intakes as high as 1500 mg/day (Pediatrics, 2000; 106: 40-4).
study of over a hundred women aged 23-84 could find no link between
calcium in the diet and BMD. The researchers concluded: 'These data do
not support the hypothesis that insufficient dietary calcium is a major
cause of bone loss in women' (J Clin Invest, 1987; 80: 979-82).
in light of such evidence, are calcium supplements of any use? The
answer is yes and no. Evidence that they’re useless comes from various
studies. In one, women aged about 40 taking calcium supplements were
monitored for four years. Despite using two different measures of bone
density, no evidence could be found that calcium arrested the normal
decline in bone strength. 'Premenopausal women in the fifth decade lose
about 1 per cent of [bone] mineral yearly, in spite of . . . ample
calcium intake,' reported the researchers (Osteoporos Int, 1995; 5:
So, supplemental calcium before the menopause appears
to be ineffective, but the ‘change of life’ changes everything. About
40 trials have investigated the benefits of calcium postmenopause. One
study pooled them together and concluded that, although the results
were not clear-cut, the weight of evidence suggested that
supplementation is valuable.
In these studies, calcium
effectiveness was measured by crude numbers of bone fractures. By and
large, increased calcium intake correlated with fewer fractures. In
four randomised trials, more than 1000 mg of calcium a day reduced
fractures by up to 70 per cent (J Bone Miner Res, 1997; 12: 1321-9). A
later study of over a hundred 60-year-old Swedish women revealed that
only the high calcium intakes - in a range of 1417-2417 mg/day - had
any effect on BMD and, therefore, the severity of osteoporosis
(Osteoporos Int, 1997; 7: 155-61).
So, calcium supplements
appear to help keep osteoporosis at bay after the menopause as long as
total calcium intake is at least 1400 mg a day. Given that women of
that age already consume about 500-600 mg of calcium in their diet,
this suggests that a daily supplement of not less than 800 mg is
advisable (J Int Med Res, 1999; 27: 1-14).
How should calcium
supplements be taken? Experiments show that maximum absorption occurs
when calcium is taken four times a day with meals, rather than all at
once, with up to 2500 mg a day considered safe (Osteoporos Int, 1991;
What are the best kinds of calcium to take? Like
other minerals, calcium cannot be absorbed in its pure mineral form; it
has to be chelated with an acid. The most common form of chelated
calcium is calcium carbonate (common chalk), which is cheap. But a
minor disadvantage is that it can only be broken down by a healthy
concentration of stomach acids, which tend to decrease with age. So
there’s a small risk that the very people most likely to benefit from
extra calcium may be least able to absorb it.
Other forms of
calcium claim to be much more bioavailable. The most common of these is
calcium citrate, which one study showed is up to 2.5 times better
absorbed than calcium carbonate (J Clin Pharmacol, 1999; 39: 1151-4).
the special value of citrate has been challenged. Trials at the
Osteoporosis Research Center in the US concluded that 'when taken with
food, calcium from the carbonate salt is fully as absorbable as from
the citrate' (Osteoporos Int, 1999; 9: 19-23). The researchers claimed
that the study favouring citrate had measured the wrong parameters (J
Nutr, 2001; 131: 1344S-8S).
Another way to increase calcium
uptake is to combine it with nutrients such as vitamins A, D and K,
magnesium and boron. The most important is vitamin D as calcium cannot
be metabolised without it. The official advice is that vitamin D should
be taken at the same time as calcium supplements (J Am Diet Assoc,
2002; 102: 818-25). Adding amounts of vitamin D as low as 3 mcg (120
IU) to calcium supplements can double the uptake of calcium (J Clin
Endocrinol Metab, 1997; 82: 4111-6).
Certainly, a vitamin
D-calcium combination has proved effective in clinical trials. A recent
study of 80-year-old women showed that 1200 mg calcium a day, taken
with 800 IU of vitamin D3, arrested normal bone mineral loss and
significantly reduced the risk of fracture (Osteoporos Int, 2002; 13:
Magnesium is also an important adjunct to calcium as it
is vitally involved in calcium deposition in bones. Not surprisingly,
therefore, magnesium deficiency itself is a cause of low bone mineral
In fact, it may be an even more powerful factor in
osteoporosis than calcium, as it can reverse the effects of ageing. Of
more than 30 women taking 250-750 mg of magnesium a day for two years,
nearly three-quarters showed bone density increases of up to 8 per cent
while those in a control group lost 1-3 per cent, the standard
age-related rate of bone mineral loss (Magnes Res, 1993; 6: 155-63).
our road test of calcium supplement products, we asked the analytical
laboratory to simply assess calcium content. But, in working out the
best value for money, we have also taken into account the
bioavailability of the calcium in these products.
Price: £6.19 for 60 600-mg tablets
generous-sized and -priced product, this delivers much more than it
claims - 650 mg of calcium per tablet, or a total bottle content of
39,000 mg. Solgar has also included vitamin D and magnesium, increasing
calcium absorbability, making it even better value for money. The cost
is low - a modest 16 p per 1000 mg. This product is far and away the
leader of the pack in terms of both quality and price.
Calcium 250 mg
Manufacturer: Nature’s Plus
Price: £8.65 for 90 250-mg tablets
also delivers more than it claims, with each tablet containing 329 mg
calcium, plus magnesium to help its absorption. The cost per 1000 mg is
a reasonable 29 p.
Price: £7.25 for 90 100-mg capsules
capsules offer 110 mg of calcium, so the whole bottle delivers just
under 10,000 mg in total. The fact that the calcium is in citrate form
significantly adds to the cost of manufacture but, according to the
latest research, does not increase bioavailability.
The cost per 1000 mg is 73 p.
Price: £12.70 for 90 150-mg capsules
is another product providing the expensive citrate form, which research
now shows may only become more bioavailable than carbonate on a totally
empty stomach. So, in practice, it has no advantages. This product will
cost you 95 p per 1000 mg.
High Strength 500mg
Price: £5.99 for 60 100-mg capsules
label boldly declares that these capsules contain 500 mg of calcium
but, if you scrutinise the small print on the label, you will find that
the true (elemental) calcium content is 100 mg - a figure confirmed by
our lab. This product works out at 91 p per 1000 mg, but it loses a
point because of the misleading label.
Price: £7.35 for 60 30-mg tablets
terms ‘elemental’ and ‘chelated’ used here sound impressive, but the
first simply means the basic calcium content, and the second means that
the calcium is bound to an acid - as, indeed, all mineral supplements
have to be. Although these 30-mg tablets weigh in at 52 mg, they’re
still poor value for money at £2.36 per 1000 mg.
Calcium 50mg (as Orotate)
Price: £12.95 for 90 50-mg tablets
is a top-notch manufacturer with a reputation for high-quality,
well-researched products. Calcium orotate is a relatively new
formulation derived from chelation of calcium with orotic acid. Orotate
is much more absorbable than the carbonate form, says Lamberts, based
on its own research. But the evidence hasn’t been published yet, so the
claim is difficult to assess.
In any case, however
bioavailable these may be, the amount of basic calcium delivered is
very low. Lamberts says it’s meant for children, but this is nowhere
stated on the label. For 1000 mg of this, you pay £2.82.
Food State Calcium 30mg Elemental
Manufacturer: Nature’s Own
Price: £4.75 for 50 30-mg tablets
this product, our lab found not 30 mg per tablet, but 46 mg. But, even
so, this offering is not good value - given its cost of £2.07 per 1000
NDS Calcium 65mg
Manufacturer: NDS Healthcare
Price: £6.95 for 42 65-mg tablets
the added magnesium and Lactobacillus bulgaricus probiotics, both of
which may improve bioavailability, this product scores poorly. Each
tablet only contains 52 mg of calcium - not what’s claimed on the label
- at a whopping £3.18 per 1000 mg.
Milk, because it is rich in calcium, is often claimed to prevent
osteoporosis, yet clinical research surprisingly shows otherwise.
Harvard Nurses’ Health Study, which followed more than 77,000 American
women for 12 years, showed no protective effect with increased milk
consumption on the risk of bone fracture - in fact, quite the reverse.
The women who drank three glasses of milk a day actually had more
fractures than those who rarely drank it (Am J Publ Health, 1997; 87:
992-7). This finding was replicated in a later study of women over 50,
where again 'dairy-product intake was significantly associated with hip
fracture' (Psychol Rep, 1999; 85: 423-30).
researchers found the same results, in general, with over 43,000 male
physicians although, in this group, the risk of osteoporosis did not
increase with higher milk consumption (J Nutr, 1997; 127: 1782-7). The
research team suggests that one explanation for these puzzling,
apparently paradoxical, findings may be that the proteins in milk, when
in the bloodstream, cause the body to release calcium from bone to
neutralise the extra acidity, thereby causing a loss of bone density.
confirmation of this theory has come from vegetarians, who tend to have
relatively low blood-protein levels. One study showed that the average
bone density of 70-79-year-old vegetarians was greater than
non-vegetarians who were 20 years younger (Am J Clin Nutr, 1972; 25:
555-8). Thus, low protein levels appear to be correlated with a lower
risk of osteoporosis - and milk comprises 3 per cent protein.
the other hand, calcium uptake from milk is higher than from other food
sources because milk contains lactose, which improves the
bioavailability of calcium (J Nutr, 1999; 129: 9-12).
other, intriguing evidence from international surveys of milk
consumption. Osteoporosis is more common in Europe and North America,
where people consume large amounts of milk products, than in African
countries, where people consume almost none. The explanation is
unlikely to be genetic as people of African descent living in the US
have more osteoporosis than their African counterparts.
Clearly, however, other dietary factors than milk may also be involved.