Time to adjust vitamin E dietary guidelines? Study evaluates fat consumption and absorption rates

09 Sep 2019 --- It has been regarded as imperative to consume fat and vitamin E simultaneously for better absorption. But now, Oregon State University (OSU) researchers have found that vitamin E can still be absorbed if a fat-containing meal is consumed within 12 hours of the nutrient’s ingestion. The findings of the study, published in The American Journal of Clinical Nutrition offer a fresh look at how we can better adjust dietary recommendations for vitamin E, as well as potentially influencing 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. Federal dietary guidelines call for 15mg of vitamin E daily (by comparison, 65-90mg of vitamin C are recommended). 

“Vitamin E, known scientifically as alpha-tocopherol, has many biological roles, one of which is to serve as an antioxidant,” says Maret Traber, Professor in the OSU College of Public Health and Human Sciences. Traber has been researching the micronutrient for three decades. 

Vitamin E is a group of eight compounds – four tocopherols and four tocotrienols, distinguished by their chemical structure. Alpha-tocopherol is what vitamin E commonly refers to and is found in supplements and the European diet; gamma-tocopherol is the type of vitamin E most commonly found in the American diet.

Study specifics and limitations
In the new study, Traber and her team used a novel technique involving deuterium-labeled vitamin E to study fractional vitamin E absorption. It was administered both orally and intravenously (IV) in a group of non-obese, non-diabetic women, aged 18-40, with normal blood pressure.

Vitamin E is a group of eight compounds – four tocopherols and four tocotrienols, distinguished by their chemical structure.Traber says that fractional absorption means just what you would think – the fraction of the dose absorbed by the body rather than metabolized 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 their body.

Deuterium, the vitamin E marker in this study, is an isotope of hydrogen with double the atomic mass of the regular version. Deuterium has both a proton and a neutron, compared to just a proton for normal hydrogen, and is a common tracer in investigations of biochemical reactions.

Study subjects at the National Institutes of Health (NIH) Clinical Center drank a liquid meal containing either 40 percent fat or no fat. Researchers then used a combination of tightly controlled dietary intakes to determine the roles fat and fasting played in vitamin E absorption.

“The study shows that vitamin E gets taken up into the intestinal cell and waits for the next meal to come along,” Traber says. “It’s in a fat droplet, sitting there, waiting to be picked up, like a cargo container and loaded onto a chylomicron truck.”

Chylomicrons are lipoprotein particles that transport dietary lipids – fats – around the body through the blood plasma. The IV portion of the study, used in conjunction with the oral dosing to calculate fractional absorption, also yielded remarkable findings, Traber notes.

“We injected the vitamin E into 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 ten minutes,” Traber says. “High-density lipoproteins quickly acquired the vitamin E, and the chylomicrons quickly disappeared from circulation into the liver.”

“The IV vitamin E we put into the body over three days, almost none of it came out again, like 2 percent of the dose,” she adds. 

“No one had ever seen that before – normally you absorb about half of what you consume. We do not know where that vitamin E that stays in the body goes, and finding that out is important in studying how much vitamin E you need to eat every day,” Traber concludes.

By Kristiana Lalou