America’s long love affair with dietary supplements may be coming to a slow sputtering end as study after study find that most of them don’t improve our health and that some may actually cause real harm. The latest finding, published yesterday in the Archives of Internal Medicine, suggests that older women who take dietary supplements, including multivitamins, folic acid, iron, and copper, have a slightly higher risk of dying over 20 years than those who don’t.
Nearly two-thirds of the 39,000 female volunteers were taking some sort of vitamin or mineral supplement when they entered the study in 1986 at an average age of 60. By 2008, more than 40 percent of the participants had died: those who took multivitamins had a 2.4 percent greater risk of death than those taking no supplements; those who took folic acid had a 6 percent higher risk, while those who took iron had a 4 percent higher risk. Calcium supplement users, on the other hand, had about a 4 percent lower risk of death.
(Vitamin D supplements, which have become incredibly popular in recent years, weren’t evaluated in the study.)
The study researchers highlighted iron supplement use as most risky since far more women took iron than, say, folic acid which was associated with a risk that could have skewed higher due to the small number of users. They said the iron findings could have been stronger since the larger the dose taken by women, the greater their risk of dealth. High iron levels have also been associated in previous research with an increased risk of heart disease, though the researchers added that they “cannot rule out the possibility’’ that health conditions leading to iron deficiency — like colon cancer, inflammatory bowel disease, or severe injuries — could have necessitated the use of iron supplements and also have led to earlier deaths.
Like other population studies that correlate some sort of lifestyle habit with health outcomes, this study doesn’t prove a cause and effect. Vitamin users may have died a little earlier in life, but that doesn’t mean the supplements were the reason. What’s more, the increased risk of death among supplement users was quite small and perhaps due to something other than supplement use.
On the other hand, supplement users tend to be more health conscious than those who shy away from the pills. So we might expect them to live longer, not less. In the current study, researchers took into account exercise habits, body weight, dietary habits, level of education, and smoking habits. They also accounted for diabetes , high blood pressure, and the use of hormone therapy.
For most of these factors, supplement users came out on top of non-supplement users. They were more highly educated, thinner, exercised more, and were less likely to have diabetes or to smoke. But they were also nearly twice as likely to have taken hormone replacement therapy since back in the 1980s, HRT was considered to be protective against heart disease, strokes, and other aging ills. We now know that HRT use actually raises the risk of such diseases, which has led to a dramatic decline in use.
When all of these differences were accounted for, supplement use didn’t appear to offer any health benefits and may have had a small downside. “Based on existing evidence, we see little justification for the general and widespread use of dietary supplements,’’ the authors concluded. “We recommend that they be used with strong medically based cause, such as symptomatic nutrient deficiency disease.’’
In other words, skip the supplements, unless your doctor tells you that you need them based on blood tests showing you’re deficient in some nutrient.