Although many Americans take vitamins as a dietary supplement, various factors may actually prevent these supplements from being properly digested and absorbed. For best results, always follow the manufacturers instructions printed on your vitamin label. Avoid taking megadoses of any dietary supplement, since excessive amounts may cause unpleasant side effects.
Fat-soluble Vitamins
Fat-soluble vitamins may be stored in your body for as long as six months. When they are consumed from foods or dietary supplements, the vitamins are transferred to fat stores, where your body keeps them until they are needed. Excess amounts go to the liver. The fat-soluble vitamins are A, K, D and E. Deficiencies of these vitamins are uncommon and are often linked to conditions that impair the body's ability to absorb fat.
Water-soluble Vitamins
Water-soluble vitamins dissolve in water and travel through the bloodstream. They are not stored by your body, and excess amounts are eliminated through your urine. Therefore, water-soluble vitamins need to be replaced more frequently than fat-soluble vitamins. Water-soluble vitamins include vitamin C and all of the B-complex vitamins. In fresh foods, water-soluble vitamins can be destroyed by cooking or storage. Colorado State University Extension recommends refrigerating fresh produce, keeping milk and whole grains away from bright light and using vegetable cooking liquid for soups and stews to maximize water-soluble vitamin content in foods.
Food Sources vs. Supplements
Whole foods are the best sources of vitamins, since they are easily digested and absorbed by the body. Whole foods also provide a wide array of vitamins, and they combine vitamins with other beneficial nutrients such as fiber, antioxidants and minerals. Nevertheless, a dietary supplement may also be helpful, especially if you consume inadequate food sources. If you are a vegetarian, pregnant, nursing or postmenopausal, or if you have a condition that prevents fat absorption in the small intestine, your doctor may suggest vitamin supplementation.
Interactions
The way that vitamins interact with other substances in the body may also affect how well they are digested and absorbed. For example, a study by scientists from the Linus Pauling Institute at Oregon State University found that smokers who take vitamin C supplements are less likely to suffer from vitamin E deficiencies. "What this and other studies like it are showing is that the protection we get from proper diet or supplements often comes from combinations of nutrients working together," says lead researcher Maret Traber. This effect is yet another reason to obtain vitamins from whole food sources.
References
- KidsHealth; Vitamins; Mary L. Gavin, MD; January 2011
- Colorado State University Extension; Fat-Soluble Vitamins; J. Anderson and L.Young; August 2008
- Colorado State University Extension; Water-Soluble Vitamins; J. Anderson and L.Young; August 2008
- MayoClinic.com; Dietary Supplements: Nutrition in a Pill?; June 2010
- EurekAlert; Study With Smokers Shows Vitamins Combine for Benefits; Maret Traber; February 2006
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