What the heck are fat-soluble vitamins? Food Safety / Nutrition

An amazing photographer and friend of mine recently posted on my Facebook page asking “what the heck are fat-soluble vitamins?”

Vitamins A, D, E, and K are known as “fat-soluble vitamins” because they dissolve in fat. The B-vitamins (thiamin, riboflavin, niacin, pantothenic acid, vitamin B6, biotin, folic acid, and vitamin B12) and vitamin C are known as “water-soluble vitamins” because they dissolve in water.

So why is this important? There are a number of reasons, the most important being that fat-soluble vitamins are more easily stored in body tissues (especially fatty tissues) over time. Since the body can store fat-soluble vitamins, it’s easier for them to accumulate to dangerous levels (i.e. vitamin toxicity) if you consume more then the recommended amount. It’s much harder (but possible) to accumulate dangerous levels of water-soluble vitamins, since they are easily excreted in the urine. Vitamins A and K cause the greatest risk to health if too much is consumed. Too much vitamin A can cause visual changes, bone pain, and liver damage. Vitamin K is involved in blood clotting, so too much can cause jaundice in newborns and blocks the effects of oral anticoagulant medications such as Warfarin (used commonly to prevent blood clots, stokes, and heart attacks).

The good news is that it’s really hard to get obtain dangerous levels of vitamins from food alone. Most mainstream dietary supplements do not contain more than the recommended daily value (DV) of fat-soluble vitamins, however it’s always important to read the label, especially in regards to vitamins A and K. More good news… most dietary supplements contain a large portion of vitamin A as beta-carotene (that orange pigment in carrots). Beta-carotene is utilized by your body as vitamin A but is not dangerous like vitamin A if you consume too much. Remember with supplements that more is not always better (i.e. don’t take more than the label and/or your doctor recommend).

Dark green leafy vegetables such as kale, collard greens, spinach, and broccoli are good sources of many fat-soluble vitamins. Mix in just a little fat (like ½ of an avocado on a salad) with these dark green leafy vegetables, and the fat-soluble vitamins will be more easily absorbed by your body.  Various meats and eggs are also a good source of vitamin A.


Comments

  1. Good article Dr. Wallace. What are the toxicity levels of Vitamins A & K?

  2. Thanks Bob. The U.S. Institute of Medicine (IOM) suggests that adult men and women should not exceed 3,000 ug per day of vitamin A. IOM has not set an limit for vitamin K but it reccomends that adult men get 120 ug per day and that adult women get 90 ug per day. There’s no need to consume more than this amount for vitamin K.

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