The National Institutes of Health began the Women’s Health initiative in 1992 to determine if there were ways to help prevent the most common causes of death, disability and impaired quality of life among mature women. This 15-year project is one of the largest prevention studies of its kind. We all want to know how to stay healthy and youthful as we age!

The clinical intervention part of the study is a randomized, double-blind, placebo-controlled clinical trial of 39,876 healthy women followed for just over a decade. Half took vitamin E and the others a placebo (“sugar pill”). Last year, the results were released finding that vitamin E proved to be of no benefit in protecting women from cardiovascular disease, stroke or cancer. And it didn’t matter what were the women’s menopausal status, hormone use, BMI (body mass index), alcohol intake, smoking status or physical activity. The researchers have now reported that vitamin E also failed to offer any benefits for preventing type 2 diabetes. There has been a lot of public interest in antioxidants and what seemed like the magic bullet for preventing chronic diseases of aging. This is a terrific illustration of why careful clinical trials on real people followed for many years are so important before we jump to conclusions about the cause or benefit of something based on observational epidemiological studies on large groups of people or select populations (“cohort”); or laboratory or rat studies.

In the laboratory and in animal experiments, vitamin E appeared to work as a vigorous antioxidant against those free radicals that can lead to diabetes. And several population studies found an association between higher intakes of vitamin E in the diet and lower incidences of type 2 diabetes. Similarly, laboratory and animal research suggested that vitamin E might prevent the accumulation of fatty deposits inside arteries and reduce clogged arteries. Large observational studies also found associations between people eating foods high in vitamin E or taking supplements and lower risks for heart disease. But as these researchers noted, those types of studies can never indicate a cause because they cannot account for bias and measurement errors and, most importantly, isolate if the effect was actually due to the thing being measured or if that was simply a marker for something else entirely. Only a well-designed, carefully conducted clinical trial can do that.