Vitamin E is has a well earned reputation as an aid for heart health. With its ability to reduce the risk of heart attacks and blood clots, it is rightly elevated to the status of an essential in the diet of millions of Americans. But like many other incredibly useful supplements, the benefits of vitamin E are dependent on proper dosage.
As long as scientists have known of the benefits of vitamin E, they have known as well that an excess of vitamin E causes bleeding by interfering with vitamin K, an essential vitamin for blood clotting. Researchers have yet to map out exactly how the two vitamins interact, but they are coming closer day by day.
In this month's Nutrition Review, Oregon State University researcher Maret Traber takes a look at the possible explanations behind the interactions of the two vitamins. A principle text she used in her exploration of the question is the Harvard based Women's Health Study, in which 40,000 healthy women over 45 years old took part over the course of 10 years. The women were assigned to either a placebo group or to a group which received vitamin E supplements of 600 international units (IU) a day. Vitamin E's protective effect was strongest for women 65 and older, while across the entire population of the study, the vitamin E group had an astonishing 24% fewer deaths from heart disease. Amongst the older populations of the study, this number rose to a 49% reduction in deaths from heart disease!
“That’s a significant benefit,” Traber said. Indeed. Still, caution must be the byword in all medical situations: “In some people high doses of vitamin E increase the tendency to bleed. Women enrolled in the study had an increase in nose bleeds.”
With this in mind, the Food and Nutrition Board (FNB) of the Institute of Medicine set the limit off the Recommended Daily Allowance (RDA) for vitamin E at 1500 IU, still well above the modest amount that proved so beneficial in the Women's Health Study.
As to how or why the two individual vitamins interact, the jury is still out. Traber's reviews suggest that perhaps a shared metabolic pathway in the liver is the cause of the vitamin E and vitamin K interaction. As vitamin E increases in the liver, vitamin K declines. To fully understand this connection, more research is needed. In the meantime, it seems very prudent to take your vitamin E, and to take it within the recommended dosage guidelines.
DSIB: Vitamin E
DSIB: Vitamin K
Nutrition Reviews Abstract: Vitamin E and K interactions – a 50-year-old problem