Safety Review: Vitamins C and E
A new review examined the results of over 50 studies regarding the safety of vitamins C and E and found that they are both safe to take at relatively high doses for extended periods of time, reports the American Journal of Clinical Nutrition (2005;81:736–45).
About 70% of Americans take dietary supplements, including vitamins, minerals, and various herbal preparations. Vitamins C and E are widely used to prevent and treat a variety of health conditions. Both are antioxidants, meaning that they help prevent the damaging effects of free radicals (unstable molecules) in the body. Free radicals are believed to play a role in the aging process and the development of many chronic diseases. Vitamin C may be beneficial for the treatment of certain types of cancer, atherosclerosis, diabetes, and allergic conditions. Vitamin E has been used to treat cardiovascular disease, epilepsy, Parkinson’s disease, and Alzheimer’s disease.
The Food and Nutrition Board of the Institute of Medicine sets dietary reference intake (DRI) values for nutrients. These values include the recommended dietary allowances (RDA), tolerable upper intake levels (UL), estimated average requirements (EAR), and adequate intake levels (AI) of nutrients based on age, health, and gender.
The upper intake level is defined as the highest amount of a nutrient that can be taken regularly by most people in the general population without posing a risk of adverse effects. The highest intake level at which a nutrient has been shown to cause no adverse effects (the no-adverse-effect level [NOAEL]) is divided by an “uncertainty factor” to come up with the upper intake level. The numerical value of the uncertainty factor is based on the quality and strength of the evidence from which the NOAEL was obtained. For example, if the NOAEL were derived from an animal trial, the uncertainty factor would be higher to provide for a wider margin of safety when extrapolating to humans. The Food and Nutrition Board’s upper intake level for vitamin E is 1,500 IU per day and 2,000 mg per day for vitamin C.
Vitamin E Safety
A recent analysis of several studies concluded that people who took more than 800 IU of vitamin E per day were 6% more likely to die from any cause than people who didn’t take the vitamin. However, when these results were further evaluated it was revealed that the increased risk of death was only found in those people taking 2,000 IU of vitamin E per day, an amount exceeding the upper intake level. At this time, there is insufficient evidence to conclude that taking 1,600 IU or less of vitamin E increases the risk of death.
In 24 separate trials using dosages of up to 3,200 IU of vitamin E per day, no significant adverse effects were documented. A notable exception was one study that showed an association between vitamin E intake and a higher incidence of hemorrhagic stroke (bleeding into the brain). This same study, however, also showed that vitamin E decreased the risk of a more common kind of stroke caused by lack of blood flow to a part of the brain, called ischemic stroke. Based on the overwhelming amount of evidence indicating the safety of vitamin E, the authors of the review determined their own UL of 1,600 IU per day for vitamin E.
Vitamin C Safety
The new study concluded that concerns regarding the safety of vitamin C have been largely unfounded. At intake levels of less than 2,000 mg per day, vitamin C does not appear to be associated with an increased risk of kidney stone formation, excess iron absorption, increased uric acid levels in the body (a cause of gout), or reductions in vitamin B12 concentrations. Another hypothesized negative effect of vitamin C is that it may actually function as a pro-oxidant, thus creating free-radical damage in the body. This claim also appears to be unsubstantiated.
Possible side effects of large doses of vitamin C include loose stools, upset stomach, and skin rashes. Vitamin C can also deplete copper in the body; therefore, people supplementing with high doses of vitamin C (over 1,000 mg per day) should take extra copper (about 1 to 3 mg per day) to prevent a deficiency of this essential nutrient. Based on the possibility of diarrhea or loose stools occurring at intakes higher than 3,000 mg per day, the authors suggest an upper intake level of 2,000 mg of vitamin C per day.
It is important to note that the upper intake levels set by the Food and Nutrition Board and reported in the new review are for healthy adults. People with a history of kidney stones, iron overload disease (hemochromatosis), or other health conditions should consult a knowledgeable healthcare provider before supplementing with these or other nutrients.
Kimberly Beauchamp, ND, received her bachelor’s degree from the University of Rhode Island and her Doctorate of Naturopathic Medicine from Bastyr University in Kenmore, WA. She is a co-founder and practicing physician at South County Naturopaths, Inc., in Wakefield, RI. Dr. Beauchamp teaches holistic medicine classes and provides consultations focusing on detoxification and whole-foods nutrition.
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