Q: I am a 65 year old woman who takes a daily calcium supplement on the advice of my doctor, but I just heard about a new study that says calcium supplements increase the risk of heart attack! What should I do?
A: A recently-published study in the British Journal of Medicine (BMJ) has caused quite a stir among the medical community and many older women who use calcium supplements to prevent or treat osteoporosis. The research, which is a “meta analysis” of several previous randomized, double-blind, controlled studies involving (mostly) women who used calcium-only supplements in doses >500mg/day, came to a very frightening conclusion: that among a subgroup of people for whom data was available, those who used calcium supplements had a 31% increase in heart attack risk compared to those who did not use calcium supplements. Median age of the participants was about 74.5 years.
At first glance, these results are indeed scary, particularly for the 10 million Americans currently diagnosed with osteoporosis (low bone mass and fragile bones), as well as the 44 million Americans estimated to be at risk for osteoporosis. Many women may be tempted to discontinue their daily calcium supplement regimen for fear of increasing their heart attack risk, and some may have already done so.
Unfortunately, this latest study’s findings have been plastered across the popular media without being placed in proper context; in fact, the study has several important weaknesses that, on closer analysis, undermine the strength and applicability of its findings. Numerous well-regarded experts have since pointed out some of these shortfalls, and in reality, this new research raises more questions than it answers. So before you toss out your calcium supplements, read on:
- The BMJ analysis only included studies involving calcium supplementation alone. However, many (most?) calcium supplements also contain Vitamin D, which is shown to be protective against cardiovascular disease and mortality in general. The selection criteria for studies to include in the analysis excluded data from close to 200 other studies, including other meta-analyses and much larger, well-known cohort studies, such as the Women’s Health Initiative study (WHI), where women used both calcium and Vitamin D supplements. (Only 5 studies involving about 8,000 people included in the BMJ meta-analysis provided patient-level data on heart attack and stroke outcomes that was used to calculate the 30% increased risk of heart attack.) Incidentally, the WHI study showed NO increased risk of cardiovascular events, such as heart attack or stroke, among almost 37,000 women taking 500mg calcium and 200 IU Vitamin D daily over a 7-year period.
- Considering calcium supplementation alone is problematic, because bone is not built from calcium alone, nor is calcium absorbed in a vaccuum. A person’s Vitamin D status is a critical consideration (most Americans are deficient), as is their intake of other bone-building nutrients such as Vitamin K and Magnesium. The absence of adequate Vitamin D, Vitamin K or Magnesium can magnify the potentially harmful effects of calcium supplements on blood vessels that could lead to heart attack, so a well-designed study would need to report on these other risk factors to determine whether its the calcium supplement alone contributing to the problem, or the interplay of a variety of nutritional factors that’s truly responsible for any possible effect of calcium on heart disease.
- The recommended daily intake of calcium for women over age 51 is 1,200mg/day, and can be met through a combination of calcium-rich foods and supplements. Several large prospective studies in the US and Europe have failed to find an increased risk of cardiovascular events among people with higher calcium intake. These observations, coupled with the WHI study discussed above, suggest that a dietary strategy that includes calcium-rich foods to meet some of the daily calcium requirements (e.g., 600-700mg/day), with a moderate calcium supplement dose (e.g., 500-600mg/day) plus Vitamin D (I recommend 800-1000 IU/day as a general rule), could be a good compromise for women at risk for osteoporosis who are concerned about possible side effects of calcium supplementation. At least three servings (and ideally four servings) of calcium-rich foods, such as milk, yogurt, cheese, calcium-fortified orange juice, calcium-fortified soy or ricemilk, cruciferous vegetables (like broccoli, cabbage, kale, collards and bok choy), tofu, canned salmon with bones, white beans, toasted unblanched almonds and dried figs should be part of every woman’s daily diet.
- If you have osteopenia or osteoporosis, before discontinuing a calcium supplement, you should discuss your individual risks versus benefits with your doctor or dietitian. You may be surprised to learn that up to 30% of people who experience hip fractures die within the first year after the fracture due to complications like blood clots or pneumonia! If you are at lower risk for heart disease (e.g., no family history, low cholesterol, no hypertension, no diabetes, not a smoker), you may jointly decide that any potential risks of moderate-dose calcium supplementation are far outweighed by the benefits of protecting your bone mass to prevent serious fractures that can have an irreversible effect on your quality of life. Your doctor or dietitian will also look at a variety of other factors, including your medication options, diet, Vitamin D levels, exercise habits and other nutritional intake, to help devise an appropriate diet and lifestyle strategy to reduce your risk of fractures that you feel comfortable with.
Tamara Duker Freuman R.D.