Many people take vitamins on a regular basis to optimize their health or to complete areas of the diet that are deficient in nutrients. Vitamin absorption depends on many factors and is difficult to measure. Understanding factors that affect absorption may improve the probability of absorbing more of the vitamins you take. It is important to note that in most cases, vitamins are absorbed best from food itself, according to "Today's Dietitian." This is why vitamins should be found in food first, with vitamins in supplements a secondary means of obtaining these nutrients.
Vitamin Quality
Many variables affect the quantity and quality of absorption of vitamins. The quality of the vitamins taken can affect absorption. A good-quality vitamin has quality ingredients and few fillers and has a manufacturer guarantee of quality and purity. The FDA requires supplement makers to test their vitamins for quality, purity, strength and composition of their products. The United States Pharmacopecia or USP symbol identifies supplements that have been tested for each of these factors, explains "Contemporary Nutrition" by Gordon Wardlaw.
Factors that Help Absorption
Each vitamin varies as to its individual factors that affect absorption. For example, fat-soluble vitamins such as A, D, E and K need fat for absorption. Without it, the amount absorbed may be small to none. One example of this was reported in the January 2004 "American Journal of Clinical Nutrition," in which scientists assessed absorption of vitamin E from a capsule compared with fat-free milk with vitamin E fortified cereal. Apparently, vitamin E is absorbed and more bioavailable when eaten from a fortified cereal as opposed to taken in a supplemental form. The vitamin E taken in pill form was virtually useless in this study. Researchers feel vitamin E would likely have been absorbed better for both cereal and the pill form if taken with fat, since vitamin E is fat-soluble. In general, food should be eaten when taking vitamins to enhance absorption.
Factors that Hinder Absorption
Foods can affect vitamin absorption negatively, as well. Taking vitamins without food can hinder the maximum absorption. Vitamins need other nutrients to transport them where they need to go to perform their functions. Vitamin B-12 attaches to the protein known as intrinsic factor. For vitamin B-12 to be used, this protein must be broken down to release it by using stomach acid, according to "Contemporary Nutrition." A study published in the July 2008 journal "Clinical Chemistry" reports coffee may interfere with appropriate levels of folate, B-12 or B-6 by preventing their absorption, and instead are excreted in the urine. This was seen in coffee drinkers who consumed more than four cups per day.
Additional Factors
Additional factors contribute to absorption of vitamins. They include how well the gastrointestinal tract is functioning and the availability of needed nutrients to transport vitamins to the absorption sites. The absorption sites also impact absorption of vitamins. For some vitamins, if there is plenty in the body already with no room for absorption, the body excretes vitamins it cannot use.
References
- "Contemporary Nutrition"; Gordon Wardlaw; 2009.
- "Today's Dietitian": Sorting Out the Science on Multivitamins and Minerals
- "American Journal of Clinical Nutrition"; Vitamin E Bioavailability From Fortified Breakfast Cereal is Greater than that From Encapsulated Supplements; Scott Leonard, et al.; 2004
- "Clinical Chemistry"; Coffee Consumption and Circulating B-Vitamins in Healthy Middle-Age Men and Women; Arve Ulvick, et al.; 2008
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