The calcium supplementation industry has grown in Western societies as a direct result of increasing vitamin D deficiency due to sun avoidance. You will recall that the main job of vitamin D in the body is to absorb calcium from the diet and lay it down in bone, thus forming normally strong, healthy bones.
Unfortunately, there is now abundant evidence that we are in the midst of an epidemic of vitamin D deficiency as more and more people adhere to public health messages about the dangers of sun exposure.1,2 So as vitamin D levels fall in the community, and not enough calcium is absorbed, osteoporosis has become widespread, resulting in a large number of fractures of long bones and the hip, particularly in our elderly.
Instead of treating the cause of this problem, that is getting people out in the sun more often, or failing that, supplementing with adequate doses of vitamin D, a whole industry of calcium supplementation has appeared.
As consumers, we now face constant advertisements about whether we are getting enough calcium, designed to get us to take calcium supplements. The dairy industry has seen an opening here to market its products as high in calcium and therefore healthy, obscuring the very real health risks associated with dairy products, particularly for people with multiple sclerosis.
It has actually taken a long time for researchers to begin to investigate whether this widespread calcium supplementation is doing any good, or more particularly, whether it is possibly doing harm. After all, many of our elderly are on drugs called calcium channel blockers, particularly those with heart and vascular disease, and intuitively it seems problematic to be giving them the very mineral whose effects we are trying to block in the body.
Recently, a number of well designed trials and meta-analyses have raised serious doubts about the safety of calcium supplementation.
A major randomised controlled trial from the University of Auckland , published recently in the British Medical Journal, examined 1471 postmenopausal women.3 Of these, 732 were randomised to calcium supplementation and 739 to placebo. Heart attacks were more common in the calcium group than in the placebo group (45 events in 31 women versus 19 events in 14 women, p=0.01). The investigators also looked at the combined end point of heart attack, stroke, or sudden death, and found that this was also more common in the calcium group (101 events in 69 women versus 54 events in 42 women, P=0.008).
It should probably come as no surprise that calcium supplementation in these elderly women was associated with increases in serious cardiovascular event rates. This increased risk might even be considered acceptable by some if the benefits of calcium supplementation were very marked. But recent work has raised doubts about whether there is really any benefit in terms of bone health from supplementing with calcium.
Interestingly, researchers from the same institution showed that calcium supplementation actually increased hip fracture risk by 50%.4 A 2007 meta-analysis from the Harvard School of Public Health reported that randomized controlled trials showed no reduction in hip fracture risk with calcium supplementation, and that an increased risk was possible.5 For other fractures, there was a neutral effect. It really is time for a re-appraisal of the whole calcium-vitamin D issue in health.
Clearly, vitamin D is very important for a variety of reasons, not least its helpful effects on mood, muscle strength, cancer, vascular and autoimmune disease.6 A real problem is that when we do supplement with vitamin D, we generally use too low a dose. We need to raise the level to a minimum of 75nmol/L to get any benefit at all for bone health7, and it probably needs to be twice that to really get the full health benefits for other conditions. We know for example that a level of 100nmol/L or so is the threshold level above which there is a great protective effect against developing MS.8
As for calcium, like many other heavily-marketed supplements, now that the evidence is coming in, we can see that it pays to be very, very selective about what supplements to take. Supplements need to be taken for a good reason, with a therapeutic aim in mind, and utilising the best available evidence to support their use.
For people with adequate vitamin D levels (and for people in most geographic regions this means supplementation with relatively large doses of vitamin D in winter), calcium supplementation is completely unnecessary.
For those who avoid the sun or cannot get much sun in winter, and those with osteoporosis, supplementation with around 5,000IU of vitamin D daily is recommended, rather than with calcium. Calcium supplementation, on the basis of current evidence, poses too great a risk to human health, and is not recommended.
- Holick MF. The vitamin D epidemic and its health consequences. J Nutr 2005; 135:2739S-2748S
- Holick MF, Chen TC. Vitamin D deficiency: a worldwide problem with health consequences. Am J Clin Nutr 2008; 87:1080S-1086S
- Bolland MJ, Barber PA, Doughty RN, et al. Vascular events in healthy older women receiving calcium supplementation: randomised controlled trial. BMJ 2008; 336:262-266
- Reid IR, Bolland MJ, Grey A. Effect of calcium supplementation on hip fractures. Osteoporos Int 2008; 19:1119-1123
- Bischoff-Ferrari HA, Dawson-Hughes B, Baron JA, et al. Calcium intake and hip fracture risk in men and women: a meta-analysis of prospective cohort studies and randomized controlled trials. Am J Clin Nutr 2007; 86:1780-1790
- Holick MF. Vitamin D: A millenium perspective. J Cell Biochem 2003; 88:296-307.
- Bischoff-Ferrari HA, Dawson-Hughes B. Where do we stand on vitamin D? Bone 2007; 41:S13-19
- Munger KL, Levin LI, Hollis BW, et al. Serum 25-hydroxyvitamin D levels and risk of multiple sclerosis. JAMA 2006; 296:2832-2838