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Sunday, September 29, 2013

Vitameatavegamin: Potential Risks of Using Vitamin Supplements

          Vitamins are nutrients required for proper metabolic function that cannot be sufficiently synthesized by the body and therefore must be obtained from external sources such as diet or resident symbiotic microbes.  Vitamins may have both widespread and organ-specific functions, during development and throughout adult life.  The letter descriptor for vitamins (Vitamin A, etc) typically refers to a group of inactive provitamin forms or “vitamers” that are metabolized into active form within the body.  There are 13 accepted vitamins in human metabolism, each with distinct sources and functions. Vitamins are either water soluble or fat soluble.  Water soluble vitamins are easily excreted and therefore must be replenished more often. Fat-soluble vitamins are stored in tissues and do not require daily intake, while sustained increased intake can lead to hypervitaminosis as concentrations increase to toxic levels.
         
Bioavailability of Vitamins
It is unclear exactly what percentage of vitamins ingested in supplement form are available for absorption and metabolic action.  One obvious factor is the fat solubility of many vitamins, which are often ingested as a pill with water, but in reality determining the “bioavailability” of vitamins ingested from supplements is very complex.  The two major factors affecting bioavailability of dietary supplements are: the ease of molecule release into solution and the presence of interfering inactive ingredients.  Additionally, a multitude of physiological factors (affected by age, sex and other variables) also have a large effect on the relative bioavailability of ingested vitamins.  For example, inherent homeostatic (equilibrium) regulation of existing nutrients may prevent utilization of further ingested nutrients while shorter digestive time correlates with improved nutrient absorption. The bioavailability of certain nutrients may also be affected by the size of the overall “load” of food or supplements ingested, and nutrients are much better absorbed when intake levels are spread out over a long period of time.
         
Variation also often exists in the actual amount of vitamin present within commercially sold supplements.  Manufacturers are required by US regulations to include greater amounts of listed vitamins within supplements than is listed on the label, in order to account for degradation and potential disparities among batches.  While most vitamins are sold at 30-100% in excess of the listed amount, examples have been reported showing actual values as low as 20% below listed amount and as high as 2.5 times the listed amount.
         
Vitamin Deficiency
The risk of vitamin deficiency varies for each vitamin depending on the individual metabolic requirements and how they are stored in the body.  Vitamins A, D and B12 are stored in large amounts by the liver, preventing deficiency conditions for several months up to a few years.  At the other extreme, niacin is very poorly stored and reserves may only last a few weeks.  Common vitamin deficiency diseases in humans include beriberi for thiamine, scurvy for Vitamin C, pellagra for niacin and rickets for Vitamin D, however deficiency diseases are rare in developed nations both due to the abundance of sufficient amounts of food and additional nutrient fortification of the food supply. 
         

Risks of Vitamin Supplementation
Many consumers may be unaware that it is possible to overdose on vitamins, especially from supplements.  The potential dangers of vitamin excess (known as hypervitaminosis) through the use of dietary supplements have been investigated, but existing data is inconclusive.  As previously mentioned, hypervitaminosis is more common for fat-soluble vitamins (A, D, E, K), which remain stored at high levels in the body long-term.  

Many recent studies have focused on long-term side effect of antioxidants, which include Vitamins A, C and E and act to counteract damaging reactive oxygen species produced from metabolic reactions.  A 2006 study combining results of several clinical trials concluded that long-term supplementation with Vitamin A or E produced a small but significant increase in mortality, however two of the trials involved smokers which may have complicated the results.  Antioxidants have also been found to reduce the beneficial effects of exercise.  A clinical trial found that Vitamin E supplementation significantly increases the risk of prostate cancer, however two other trials reported beneficial effects of Vitamin E on prostate cancer incidence and survival.  Additionally, an opinion piece from James Watson (of DNA structure discovery fame) comments that antioxidant vitamin supplementation may inhibit both the treatment and prevention of cancer by blocking the induction of cell death. Differing studies also exist concerning the health effects of other vitamins, reporting that vitamin supplementation may reduce the likelihood of infection while in contrast reducing lifespan in older women.
         
Conclusion
          The purpose of this post is not to discourage use of all vitamin supplements.  I use daily vitamin supplements myself, and supplementation can be very useful in developing nations and individual cases of an insufficient diet or unique metabolic requirements.  For example, folic acid supplementation is recommended for pregnant women, even in the United States where adequate diet is available.  Any potential risk from long-term use of supplements is either small or inconclusive in most cases; however the same may also be true for their benefits.  Feel free to take supplements as long as you remain within the recommended dose, just know that their effects may be minimal if already ingesting a healthy western diet.

4 comments:

  1. Except ...what do you consider a healthy western diet? Look around- most school age children that I know subsist on a skimpy breakfast, imported lunch from a few different purveyors 'approved by' , meaning given the contract by, the school board. This consists of frozen pizza once a week, mystery croquettes, mac and cheese, and occasionally a piece that one is willing to eat. Then they are fed candy by the teacher as a reward for the slightest effort, going home to fast food and coke. The really progressive family will offer sports drinks or sugary juice instead. In my neighborhood the kitchens are pristine, as noone wants to mess them up except the day before the 'help' is coming.

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    1. A healthy western diet is basically the food pyramid (although that has been edited) - a mix of fruits, vegetables, proteins, grains, and little sugar.

      The point is just that sugar is bad no matter in what form

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  2. This comment has been removed by the author.

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  3. A recent paper explained how ingesting antioxidants can be detrimental for cancer progression, following up on Dr. Watson's proposal
    http://www.nejm.org/doi/full/10.1056/NEJMcibr1405701

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