New insight shows that even though vitamin E is fat soluble you don’t
have to consume fat with it to enable absorption as it will sit in the
intestinal cell and wait for the next meal to come along.
“We used to think you had to eat vitamin E and fat simultaneously. What our study shows is that you can wait 12 hours without eating anything, then eat a fat-containing meal and vitamin E gets absorbed,” said the study’s corresponding author, Maret Traber of Oregon State University, a leading authority on vitamin E.
Vitamin E, known scientifically as alpha-tocopherol, has many biologic roles, one of which is to serve as an antioxidant.
Federal dietary guidelines call for 15 milligrams of vitamin E daily (by comparison 65-90 milligrams of vitamin C are recommended). The new research could play a role in future vitamin E guidelines.
Vitamin E in human diets is most often provided by oils, such as olive oil. Many of the highest levels are in foods not routinely considered dietary staples, such as almonds, sunflower seeds and avocados.
“There’s increasingly clear evidence that vitamin E is associated with brain protection, and now we’re starting to better understand some of the underlying mechanisms,” Traber said.
In this latest study, Traber and collaborators used a novel technique involving deuterium labelled vitamin E, administered both orally and intravenously, to study fractional vitamin E absorption in a group of non-obese, non-diabetic women ages 18-40 with normal blood pressure.
Fractional absorption means the fraction of the dose absorbed by the
body rather than metabolised and excreted. Fractional absorption
dictates how much of something, in this case vitamin E, a person needs
to take to maintain the correct level in his or her body.
Study subjects at the National Institutes of Health Clinical Center were given both oral and IV vitamin E and drank a liquid meal containing either 40% fat or no fat.
“What this study says is, vitamin E gets taken up into the intestinal cell and sits there and waits for the next meal to come along,” Traber said.
The IV portion of the study, used in conjunction with the oral dosing to calculate fractional absorption, also provided interesting findings. “We injected the vitamin E in a lipid emulsion and expected it would take some time to disappear from the plasma and them come slowly back into circulation, but it was gone within 10 minutes,” Traber said.
“High-density lipoproteins quickly acquired the vitamin E. The IV vitamin E we put into the body over three days, almost none of it came out again, like 2% of the dose”.
“No one had ever seen that before—normally you absorb about half of what you consume. That vitamin E that’s staying in the body, we don’t know where it goes, and finding that out is important for studying how much Vitamin E you need to eat every day”.
Vitamin E is a group of eight compounds – four tocopherols and four tocotrienols. Alpha-tocopherol is what vitamin E is commonly refers to. “Plants make eight different forms of vitamin E and you absorb them all, but the liver only puts alpha-tocopherol back into the bloodstream,” Traber said. “All of the other forms are metabolised and excreted.
“That’s really exciting, because it explains why the liver needs an alpha-tocopherol transfer protein but the intestine does not.”