No discussion of selenium and vitamin E supplements would be complete without mentioning the potential side effects of these popular supplements. The literature reminds us of the potential harm that could exist if someone is selenium deficient. For example, Keshan's disease is a dilated cardio-myopathy that is found in individuals with little to no selenium intake (less than 19 |g/day) in certain areas of China and other countries.61 However, this disease is a rare finding in most countries, and should not be used as evidence to espouse the use of selenium supplements. In fact, one might equate this problem with that of scurvy and vitamin C, which is difficult if not impossible to find these days in many countries.
Excess levels of selenium ingestion can be quite toxic. Selenium supplements have been associated with gastrointestinal problems, pathologic nailbed changes and the loss of fingernails, temporary hair loss and even fatigue.62 However, at 200 |g/day these side effects, apart from some gastrointestinal upset were not observed in a past trial,3 but for the patient who believes in the 'more is better' theory, this could represent a potential problem. Clinicians need to advise patients on the potential harm that could result from taking too much supplemental selenium. A CDC report from 1983 highlights the dangers of high selenium intake.62 Individuals were taking a selenium supplement that actually contained hundreds of more micrograms and milligrams than was reported on the purchased bottle. This resulted in temporary and permanent nail and hair loss, and fatigue that was mentioned earlier.
Vitamin E, when combined with blood thinners of all types, may increase the risk of internal bleeding.38 It is notable that smokers in the ATBC trial had an increased risk of hemorrhagic stroke at only 50 mg of vitamin E daily. Other clinical studies have demonstrated that obtaining over 1000mg of supplemental vitamin E daily may be harmful.63-65 For example, it can reduce the body's absorption of other antioxidants (like vitamin C) and may act as a pro-oxidant at these levels rather than an antioxidant, especially if you are not a smoker.66 It seems that, if any of these supplements have an impact on health, then they do so within a certain window period. Too little does not do anything and too much has either a negative or no impact. This will be a real challenge for future supplement trials: deciding on the right supplement, at the right dosage, and which can give maximal efficacy and minimal side effects.
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