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Randomized controlled trials show that daily vitamin D supplementation appears to reduce risk of acute respiratory infections in children and adolescents, but it does not seem to make a difference in adults. Nor does vitamin D appear effective for boosting antibody responses to influenza vaccination.
What about vitamin E? In most places, you’ll read that there are eight different tocopherols and tocotrienols that are collectively known as vitamin E, but only alpha-tocopherol has been shown to protect against human vitamin E deficiency. So, alpha-tocopherol is the only bona fide vitamin E, and is the one found in vitamin E supplements.
There are observational data suggesting those self-reporting supplementation with vitamin E have, for example, better pneumonia outcomes. But only interventional trials can prove if this is the case. Compared to placebo supplements, vitamin E was able to significantly boost immunity to hepatitis B and tetanus vaccinations (though not to diphtheria or pneumonia). One randomized controlled trial found that vitamin E supplementation of the elderly did not cut down on lower respiratory tract infections (like pneumonia), but did reduce the incidence of upper respiratory tract infections (like the common cold) by about 20 percent over one year. But another study using the same dose found no preventive benefit, and vitamin E supplementation actually made the infections they did get worse––with a greater number and severity of symptoms, including a greater likelihood of fever and activity restriction.
By far the largest study on vitamin E and respiratory infections was the Alpha-Tocopherol, Beta-Carotene Cancer Prevention (ATBC) Study that randomized nearly 15,000 smokers to vitamin E or placebo for about five years. No overall effect was found either way between the vitamin E and placebo groups. But upon subgroup analysis, it appeared that while lighter smokers living in cities appeared to benefit with about a 50 percent lower risk of catching the common cold, vitamin E appeared to be a detriment to heavier smokers living outside of cities––resulting in about a 50 percent increased risk. “Accordingly,” concluded the investigators, “caution should be maintained in public health recommendations on vitamin E supplementation until its effects are better understood.”
The pneumonia results from the same study took a similar turn. No overall effect of vitamin E compared to placebo, but upon further analysis, vitamin E appeared to decrease pneumonia risk among lighter smokers who exercised, yet it increased pneumonia risk among heavier smokers who did not. Higher pneumonia rates were also noted in those randomized to vitamin D, and were either low or high body weight––but only, apparently, among those with high dietary vitamin C intake. Heavy smokers who got a lot of vitamin C also seemed to have higher tuberculosis rates on vitamin E compared to placebo. This kind of slicing and dicing of data is frowned upon, as it can spawn spurious connections, and so these findings are regarded only as exploratory for further research directions.
Overall mortality in the ATBC Study was similar between the vitamin E and placebo groups, though again there were subgroups that appeared to have their lives cut short or extended. There have been dozens of controlled clinical trials on vitamin E, and most meta-analyses found a small but apparent real increase in the risk of mortality among those randomized to vitamin E. In other words, those who buy vitamin E supplements may be in effect paying to live a shorter life. Across 46 trials, 12 percent died in the vitamin E groups, versus about 10 percent in the placebo groups. (This is similar to the increase in mortality seen with beta carotene supplementation—approximately 14 percent versus 11 percent across 26 randomized trials.)
The goal of the ATBC Study was to see if taking antioxidant supplements like vitamin E or beta carotene could help prevent lung cancer in smokers. Vitamin E had no effect on lung cancer, and beta-carotene unexpectedly actually increased lung cancer rates. But vitamin E did, incidentally, appear to reduce incident prostate cancer rates. This helped inspire the SELECT study, the largest cancer prevention trial ever performed. More than 35,000 men were randomized to take vitamin E, selenium, both, or neither (just placebos). The selenium didn’t appear to matter, but those randomized to the straight vitamin E group ended up with a 17 percent greater risk of developing prostate cancer. If 100 men took vitamin E for a decade, we would expect to see one or two of them be diagnosed with prostate cancer that they otherwise wouldn’t have gotten had they wasted their money on sugar pills instead.
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