Did you toss your calcium pills in the trash — and then worry about getting osteoporosis — after a new study concluded that calcium supplementation could increase heart attack risk? Let’s not be too hasty.
Here’s what that widely publicized study really showed… and what we women should do with the information.
As reported in the journal BMJ, investigators analyzed data from 11 clinical trials in which nearly 12,000 patients — mostly women age 70 or older — were randomly assigned to receive calcium supplements or placebos for an average of nearly four years. The shocker: People who took 500 milligrams (mg) or more of calcium daily were about 30% more likely to have a heart attack than those who did not take calcium.
Many physicians, including me, were surprised by these findings, as other research (detailed below) suggests that calcium generally has a neutral or even protective effect on the heart. Still, this study raises the possibility that calcium supplements should not be used as widely as they are now.
The concern: In recent years, researchers have discovered that vascular calcification (calcium buildup in atherosclerotic plaques in the arteries) is a risk factor for heart attacks… and it may be that overzealous consumption of calcium can contribute to vascular calcification or even to the development of atherosclerosis itself. But before you panic, consider the following…
The BMJ study’s results do not necessarily apply to dietary calcium. Indeed, a high intake of calcium from foods, including calcium-rich low-fat dairy products, has been associated with lower risks for various heart attack risk factors, including diabetes… high blood pressure… and metabolic syndrome, a cluster of symptoms that includes abdominal obesity, high triglycerides, high blood pressure, high blood sugar and low HDL (good) cholesterol.
Why might dietary calcium have more favorable effects than supplemental calcium? Because dietary calcium may interact with other nutrients in food to yield health benefits… and because calcium from food may be absorbed into the bloodstream more slowly than calcium from supplements, thus reducing the likelihood of high blood calcium levels.
The BMJ study findings do not necessarily apply to calcium supplements taken in combination with vitamin D. The BMJ study focused on calcium supplements taken alone, without vitamin D. However, many calcium supplements sold in the US also contain vitamin D. Available research suggests that the same heart risks are not found with such combination supplements because vitamin D regulates calcium metabolism, the mechanism by which the body maintains appropriate calcium levels.
Example: The Women’s Health Initiative — in which about 36,000 postmenopausal women were randomly assigned to take either placebos or 1,000 mg of calcium plus 400 international units (IU) of vitamin D per day — did not find an increased risk for either vascular calcification or heart attack.
According to the BMJ study, calcium supplementation did not increase heart attack risk in people whose dietary calcium intakes were less than about 800 mg per day, This bolsters the idea that excess calcium might be responsible for the BMJ study results. It may be especially true for older people who have decreased kidney function.
WHAT WOMEN SHOULD DO
To me, this study has a clear take-home message. For bone health, I advise that you get the currently recommended amount of calcium each day, taking into account both your dietary and supplemental calcium sources — but avoid ingesting more than this amount. Many experts recommend 1,000 mg of calcium per day up to age 50 and 1,200 mg per day thereafter… as well as about 800 IU per day of vitamin D from food and/or supplements. Bottom line: If you get this much calcium from food alone, skip the supplements. If you do not get sufficient calcium from your diet, make up the difference by supplementing (and take care to get enough vitamin D, too).
To estimate the amount of calcium in your diet, check the calcium content of specific foods on the USDA Web page at http://www.ars.usda.gov/Services/docs.htm?docid=18877… on the National Institutes of Health Web page at http://ods.od.nih.gov/factsheets/Calcium.asp… and/or on food labels.
Rich dietary sources of calcium include…
Yogurt, plain, low-fat: 415 mg per cup.
Sardines, canned with bones: 325 mg per three-ounce serving.
Milk, low-fat: 305 mg per cup.
Cheddar cheese: 204 mg per ounce.
Salmon, canned with bones: 181 mg per three-ounce serving.
Collard greens: 178 mg per Â½ cup chopped and cooked.
Figs: 155 mg for five figs.
Cottage cheese (1% milk fat): 138 mg per cup.
Unless you consume a lot of dairy products, you are unlikely to get too much calcium from food alone. But: It is easy to get too much supplemental calcium — so check labels not only on your calcium tablets but also on your multivitamins, calcium-plus-vitamin-D supplements and any calcium-containing medications that you may be taking.
Source: JoAnn E. Manson, MD, DrPH, is a professor of medicine and women’s health at Harvard Medical School and chief of the division of preventive medicine at Brigham and Women’s Hospital, both in Boston. She is one of the lead investigators for two highly influential studies on women’s health — the Harvard Nurses’ Health Study and the Women’s Health Initiative. Dr. Manson is the author, with Shari Bassuk, ScD, of Hot Flashes, Hormones & Your Health (McGraw-Hill), and a columnist and advisory board member for HealthyWoman from Bottom Line.
By JoAnn E. Manson, MD, DrPH