How Vitamins A, D, E, and K Interact - Part 1: The Players
Posted Nov 17 2008 4:15am
Last week, we discussed some of the various diseases that can result from vitamin D deficiency. Today, I want to look at the other three fat-soluble vitamins - A, E, and K - and see how these four vitamins function within the body.
What Are The Four Fat Soluble Vitamins?
Vitamin A - The Vision Vitamin Vitamin A is probably most well-known from your mother’s admonitions to “eat your carrots, so you can see well.” One of the many roles of vitamin A is eyesight, but this vitamin is also key for proper gene transcription, immune function, embryonic development, bone metabolism, and (Teenagers take note!) skin health and acne prevention. Vitamin A also affects the production of growth hormone and testosterone.
Vitamin A comes in two main forms: retinol and beta-carotene. Animal foods provide retinyl palmitate, which is changed in the small intestine to retinol, known as “true” vitamin A as it is nearly ready for the body to use (retinoic acid is the active form of A). Beta-carotene, on the other hand, must be converted to retinol or vitamin A, and comes from plant foods. Because retinyl palmitate is pre-formed vitamin A, it is theoretically possible to overdose (though exceedingly rare). With beta-carotene on the other hand, it’s highly unlikely that one will exceed the body’s requirements as the conversion factor of beta-carotene to retinol is about 12-to-1.
Vitamin D - The Sun Vitamin I won’t go too much into what vitamin D is here or how it’s made in the body since it was covered last Thursday. But I will get a bit more in-depth. There are two major forms of vitamin D (along with three other forms): D 2 and D 3. D 2 comes from plant and fungal sources, while D 3 comes from animal sources, most notably your own skin when exposed to sunlight.
To sum up last week’s article, this vitamin is responsible for maintaining blood levels of calcium and phosphorus, growing bone, and shoring up the immune system. Studies have shown that deficiency can play a role in myriad diseases, from rickets to Alzheimer’s, Parkinson’s, Rheumatoid Arthritis, and skin cancer, and that sufficient levels are protective against some skin infections and radiation.
Vitamin E - Tocoph-a-what? Vitamin E is actually a set of eight related substances known as tocopherols and tocotrienols. The four tocopherols are alpha, beta, gamma, and delta (creative, I know), with alpha-tocopherol being the form preferentially absorbed and used by humans. The tocotrienols are similarly named. Vitamin E is largely used within the body as an anti-oxidant. Each of the eight forms of vitamin E has about the same antioxidant potential, though some research suggests that the tocotrienols are more potent in their anti-oxidant and anti-cancer effects than are the tocopherols.
However, new research suggests that vitamin E may serve most importantly as a signaling molecule, not as an anti-oxidant. Vitamin E also appears to have a function in heart disease prevention through regulation of phosphorylation cascades. Further, a metabolite of delta-tocopherol has a regulatory effect on sodium in the blood, possibly contributing to a blood pressure lowering effect. Finally, vitamin E has proven in rats to reduce infertility, improving sperm production in males and the ability of females to carry to term.
Unfortunately, most multi-vitamin manufacturers ignore the other seven forms of vitamin E and provide predominantly alpha-tocopherol. While alpha-tocopherol is the most readily absorbed of the eight forms, I’m sure I don’t need to say that the other seven forms obviously serve important roles in the body. Studies on vitamin E typically supplement solely with alpha-tocopherol which leads to reduced concentrations of gamma- and delta-tocopherols.
Vitamin K - Activator X The final fat-soluble vitamin is vitamin K. It was identified by Dr. Weston A. Price as a compound he called “Activator X”. As with vitamins A and D, there are two main forms of vitamin K, known as K 1 and K 2. K 1 is the predominant form of vitamin K in the diet, coming from plant foods. K 2 consists of MK-4 and MK-7 forms, which are found in animal foods and natto.
Vitamin K deficiency can result in calcification of soft-tissue, atherosclerosis, and uncontrolled bleeding owing to K’s role in blood clotting. Further, deficiency is associated with malformed bones and prostate cancer.
Once again, we see that the MK-4 form of the vitamin, the form that comes pre-formed from animal foods, is much more highly usable than the K 1 form (and also more so than the MK-7 form produced by bacterial fermentation). Humans are very inefficient at converting K 1 to K 2.
Stephan at Whole Health Source has done an entire series on vitamin K and its role in disease prevention (which is where I got much of the above information). It’s good reading and goes far more in-depth than the skim I just gave the issue.
Today, we looked at the four fat-soluble vitamins in isolation. In the next installment of this series, I’m going to discuss the far more important interplay between these vitamins once they are in the body.