Professor Ian Reid of University of Auckland has recently published an excellent review on calcium supplementation and cardiovascular disease.
People are often worried about taking calcium because it’s commonly reported in the media that calcium supplements may increase your risk of cardiovascular disease. In addition, in his review, Dr Reid did find that many people are taking too much calcium, and it is damaging their cardiovascular system.
The article is free to download.
During the 1980s and 1990s, calcium supplements became widely used in the prevention and treatment of osteoporosis. Probably a number of factors contributed to their popularity, including evidence that increased intakes were associated with positive calcium balances, and the absence of other clearly effective therapies for managing osteoporosis.
There is now clear evidence that calcium supplements have small positive effects on bone mineral density in randomized controlled trials, and they appear to reduce total fracture risk by as much as 10% (of borderline significance), although they may actually increase hip fractures.
As far as calcium’s effect on cardiovascular health, Reid’s group collected data in 11,921 randomized subjects, 93% of all subjects participating in trials using calcium alone. They found that in this analysis, there was a 27% increase in risk of myocardial infarction (p=0.04) and non-significant upward trends in stroke (relative risk 1.12, p = 0.25) and death (relative risk 1.07, p=0.26).
Calcium treatment was associated with an increased risk of myocardial infarction in people with dietary calcium supplementation above the median of 800 mg/day (hazard ratio 1.85), but no increased risk in those with supplemental calcium intake below the median of 800 mg of calcium per day (hazard ratio 0.98).
The Reid group also carried out a meta-analysis of all studies using either calcium or vitamin D for which cardiovascular event data are available. In this analysis, they found a 24–26% increase in risk of myocardial infarction (p = 0.005) based on a trial population of more than 28,000 subjects. The increase in risk of stroke appears to be less (15%–19%) and sits at the borderline for statistical significance. It did not matter if vitamin D was taken with the calcium.
Reid thinks the mechanism of action by which calcium supplements increase risk of cardiovascular events is that higher doses of calcium supplements produce transient increases in serum calcium, which promotes vessel calcification.
“Individuals considering taking or prescribing calcium supplements are left with a conundrum. There is equivocal evidence of benefit to bone health, which needs to be balanced against steadily increasing evidence of adverse cardiovascular risk. This balance was assessed in the Bolland meta-analysis of calcium monotherapy, which calculated that treating 1000 people with calcium supplements for five years would cause an additional 14 myocardial infarctions, 10 strokes and 13 deaths, while preventing 26 fractures. . . Thus, the available data suggest that the widespread use of calcium supplements in older individuals is doing more harm than good and should be abandoned. . . The absence of a clinically significant association between calcium intake, bone density and fracture risk over the range seen in Western populations, suggests that calcium is not a critical determinant of bone health in most individuals taking a balanced Western diet.”
Compare Professor Reid’s conclusion to a review published last year by Professor Robert Heaney on the very same topic: calcium supplements and cardiovascular disease.
Along with Dr. John Hathcock and others at the Council for Responsible Nutrition, Professor Heaney highlighted the following in their review:
- Fifty-four percent of Americans do not meet the estimated average requirement for calcium with diet alone.
- Emerging evidence suggests that calcium supplementation may be associated reduced risk of the development of colon polyps, cancers, and pre-eclampsia.
- Over the last two decades, calcium supplementation has been increasing, with 43% of the US population and 70% of older women now using calcium supplements. During this same time, cardiovascular disease has been steadily decreasing.
- Among 16 studies reviewed in this article involving over 358,000 individuals, there was no indication of a connection between calcium intake and atherosclerotic heart disease or stroke. However, keep in mind that these studies were not all randomized controlled trials like in Reid’s meta-analysis.
In my opinion, based on these two reviews, it is crucial, when and if you decide to supplement with calcium, that you keep the dose below 800 mg/day. And keep in mind many people do not even need that much. The main problem with the studies used in Professor Reid’s meta-analyses was the high dose of calcium used, up to 2,000 mg/day. If you take calcium supplements, don’t take more than 250 to 300 mg at any one time and take it with your meals.
To decide if you need calcium supplements you need to do a dietary analysis on yourself. The easiest way to get enough calcium is to eat dairy, including yogurt and cheese. For vegans, it is a little more difficult (but can be done):
The other point I want to make is that bones need more than vitamin D and calcium, a lot more. The chronic low-grade metabolic acidosis present in many of our bodies certainly contributes to osteoporosis.
Bones need a plethora of minerals, not just calcium and magnesium, but also silica, which is hard to get unless you drink beer or eat whole grain foods, boron, zinc and manganese among others. Vitamin K2 appears to be important as well. If you just take vitamin D and calcium, and have a typical American diet, I suspect your osteoporosis will not improve.
Finally, I think, but cannot prove, a common cause of osteoporosis is widespread subclinical vitamin A toxicity. I recently spearheaded a letter to the Food and Nutrition Board signed by 19 nutrition experts. You can read it here.