NO ONE HAS IT HARDER THAN THEIR FATHER DID:

[A]s striking as these results on both vitamin D and vitamin E are, they fall short of the standard for causality. These studies were not randomized controlled trials, which means other factors could have influenced their outcomes. The authors did try to adjust for some variables -- age and whether the subjects smoke, for example -- but these may not be sufficient. Yet people believe the results: 25 percent of adults reported taking vitamin E in 1989, and the share rose to almost 40 percent by 2003.

As is often the case, striking observational results like these were followed by large randomized controlled trials -- many of them. A study run through the National Institutes of Health called the Women's Health Initiative analyzed the impact of vitamin D and calcium supplementation in 36,000 post-menopausal women. Another large trial out of Harvard -- the Physician's Health Study -- looked into vitamin E supplementation among 14,000 male physicians.

In these trials, participants were randomly assigned to take supplements. Because the assignment was random -- and the trials were big -- the demographic and health characteristics of the supplement group and the non-supplement group were similar before the study started. When researchers looked at participants' health over the long term, they could therefore be confident that any differences they saw across groups were due to the supplements, and not some other factor.

When the results of these studies came out, they largely refuted the idea that these supplements offered benefits. Vitamin E appears to have no impact on cancer or heart disease. Results from the Women's Health Study, released in 2005, showed no relationship between vitamin E supplementation and overall mortality. Later results from the men in the Physicians' Health Study showed the same: no relationship.

For vitamin D, the randomized trials (nicely summarized here) refuted virtually all of the purported benefits to diabetes, weight loss and cancer. For elderly women, there is some evidence of a small reduction in mortality with supplementation, but well below what was seen in observational data and only marginally statistically significant.

The bottom line is that there is simply very little evidence that these supplements matter. The best-case scenario is if you are an elderly woman who is deficient in vitamin D -- then a supplement might help a little. Still, in the 2009-2010 NHANES, about 30 percent of the non-elderly-female population took supplements.

And it's not just vitamins D and E. The Physicians' Health Study also looked into vitamin C and a one-a-day multivitamin and found the same results: no impacts on cancer or cardiovascular disease. Of course there are exceptions -- folic acid is generally a good idea for pregnant women -- but the data increasingly suggests that most people simply do not benefit from supplements.

To be clear: Serious vitamin deficiencies can cause serious problems (scurvy in the case of vitamin C, rickets in the case of vitamin D, beriberi for vitamin B).1 But if you live in the developed world and eat a normal diet -- even a pretty unhealthy one -- you will be nowhere near this kind of deficiency.

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