Conflicting reports about the potential benefits of dietary supplements can make a person's head spin.
That's certainly been the case with vitamin E. Some human studies have shown this antioxidant to play a protective role in cardiovascular disease, while other studies have shown it to have no effect at all. So the question on many consumers' minds is, “Should I increase my vitamin E intake or not?”
Scientists at Southwest Foundation for Biomedical Research (SFBR) don't have a definitive answer to that question yet, but their research with baboons has shed light on why human studies have been contradictory and why the answer isn't as clear cut as one would hope. In fact, the answer might be “yes” to one individual and “no” to another.
In the September issue of The American Journal of Clinical Nutrition, SFBR scientists explain their findings from a study with 250 baboons on a diet with equal levels of dietary fat and cholesterol but varying degrees of vitamin E concentration.
“What we found was that vitamin E had a significant effect on cardiovascular disease risk factors, but those effects went in opposite directions. Some of the effects were positive, and some were negative,” said Dr. David Rainwater, a scientist in the SFBR Department of Genetics and the lead author on the paper. “This leads us to believe that the discrepancies in human studies are due to which effect is emphasized in the group of people studied.”
Rainwater explained that the baboons that consumed higher levels of vitamin E had lower levels of oxidized LDL cholesterol. “Oxidized LDL is believed to be a major player in terms of promoting atherosclerosis (the build up of fatty plaques in the arteries) and in cardiovascular disease in general,” he said. “So in this way, vitamin E was shown to play a protective role.”
However, findings about vitamin E's effect on HDL, the “good cholesterol,” were contradictory. Higher levels of vitamin E in the diet increased levels of apolipoprotein A-1 (apo A-1), which helps HDL remain soluble in the blood. On the other hand, it decreased the average particle size of HDL.
“And that is a bad thing, because a decrease in the size of HDL particles is generally associated with an increase in atherosclerosis,” said Rainwater. “So we found that vitamin E is exerting two different effects on HDL properties, one positive and one negative with respect to heart disease.”
While the contradictory results are frustrating, the problem might not be so much with vitamin E as it is with our genes. This scientific investigation further revealed that vitamin E's positive influence on apo A-1 levels were not genetically influenced, but genes do appear to play a role in the negative effect vitamin E can have on HDL particle size.