Despite substantial research in recent years that shows dietary supplements offer no benefit to most healthy people and can often be harmful, slightly more than half of American adults use such supplements — about the same percentage who used them in 1999, according to a study published this week in the Journal of the American Medical Association (JAMA).
A second study, published Tuesday in the Journal of the American Heart Association, underscores why many experts are concerned about this steady, widespread use of dietary supplements. It found an association between calcium supplements — but not calcium-rich foods — and an increased risk of developing heart disease.
Let’s start with the calcium study.
Calcium’s source matters
For the study, researchers at Johns Hopkins University analyzed 10 years of data on more than 2,700 individuals, aged 45 to 84, who had volunteered to be part of the long-running Multi-Ethnic Study of Atherosclerosis. The participants had filled out questionnaires about their dietary habits and had been interviewed about what drugs and supplements they took daily. They had also undergone two cardiac computed tomography (CT) scans (one when they entered the study and another 10 years later), which measured calcification in the heart’s arteries — a marker of heart disease risk.
After adjusting the data for such factors as weight, exercise habits, education and income, the researchers found that participants in the top fifth in terms of how much calcium they consumed (greater than 1,400 milligrams of calcium daily) — no matter what the source — had a 27 percent lower risk of heart disease, compared to those in the bottom one-fifth (less than 400 milligrams of calcium daily).
The researchers then calculated the risk based on the source of the calcium: food or supplements.
They found that people who took calcium supplements (and 46 percent of the study’s population reported doing so) were 22 percent more likely to have a coronary artery calcification score that rose over the decade of the study to a level that indicated the development of heart disease.
No increase in heart disease risk was observed, however, among the study’s participants with the highest intake of calcium from food alone (more than 1,022 milligrams daily).
“When it comes to using vitamin and mineral supplements, particularly calcium supplements being taken for bone health, many Americans think that more is always better,” said study co-author Dr. Erin Michos, a cardiologist at Johns Hopkins University, in a released statement. “But our study adds to the body of evidence that excess calcium in the form of supplements may harm the heart and vascular system.”
Caveats and concerns
It’s important to point out that this was an observational study. Its findings, therefore, do not prove that taking calcium supplements increases the risk of heart disease.
Yet, as background information in the study points out, other studies — including findings from the large Women’s Health Initiative — have also raised concerns about a possible link between calcium supplements and an increased risk of heart disease-related events, such as strokes and heart attacks.
Furthermore, research has shown that calcium (and vitamin D) supplements are not effective at preventing osteoporosis, which is the primary reason 43 percent of U.S. adults take them.
Indeed, the JAMA study published this week, which examined trends in supplement use, found that the use of calcium supplements has fallen only slightly in recent years.
A constant trend
But, then, that study discovered that the use of dietary supplements in general has remained constant since the late 1990s and early 2000s. Using data from a series of National Health and Nutrition Examination Surveys (NHANES), researchers found that 52 percent of U.S. adults reported in 2011-2012 having used supplements during the previous 30 days — the same percentage who reported doing so in 1999-2000.
Multivitamin use did decline a bit (from 37 percent to 31 percent), as did the use of several “one-off” supplements, such as vitamin C, vitamin E, selenium, ginseng, ginkgo biloba and garlic — perhaps because of research showing they offered no benefit. But other dietary supplements found to be ineffective — such as glucosamine and chondroitin — continue to be popular.
And several supplements increased in use between 1999 and 2012, including omega-3 fatty acids, lycopene, vitamin D and probiotics.
‘The supplement paradox’
“Why would consumers continue to use supplements after high-quality trials found many of these products to be no more effective than placebo?” asks Dr. Pieter Cohen of Harvard Medical School in an accompanying editorial.
“One factor may simply be that consumers are not aware of these negative results, and so continue to use the products they have been using for years,” he writes. “… Another factor may be that these findings are counter-intuitive: avoiding a multivitamin seems to run counter to everything patioents have been taught about the importance of consuming enough vitamins and minerals.”
But a major known reason for this “supplement paradox” — the continuing robust use of supplements despite their negligible benefits — he says, “is that the law affords manufacturers significant leeway to advertise supplements for a broad spectrum of conditions … even after high-quality studies that show no meaningful clinical differences between supplements and placebos are published.”
Cohen calls on legislators to “focus on developing regulatory reforms that provide consumers with accurate information about the efficacy and safety of supplements and on improving mechanisms for identifying products that are causing more harm than good.”