Thursday, June 19, 2008

Ask the Expert: How much Vitamin C is too much?

Q. How much Vitamin C is too much?

A. Vitamin C is an important molecule. It is involved in the synthesis of collagen (an important structural material), aids in wound healing and drug metabolism, increases the absorption of iron, and may enhance the immune system. Usually, people can tolerate large doses of Vitamin C without any significant adverse effects. Signs of ingesting too much vitamin C can include stomach irritation, gas, and diarrhea. People who might want to take more vitamin C than the recommended daily allowance are the elderly, diabetics, smokers, and alcoholics. This is because the elderly and alcoholics usually have poor diets lacking adequate amounts of vitamin C. Diabetics, because of their low insulin levels, may have poor vitamin C transporting capabilities to the cells that require vitamin C. Smoking adversely affects the metabolism of vitamin C in the body, leading to lower levels of vitamin C in the blood. The RDA for adults is 60 mg/day. The most health benefits may be derived from doses of 150-200 mg/day. Megadoses of 1000-2000 mg/day may lead to side effects, so in general it is best to stay below 1000mg/day. Vitamin C toxicity is very rare.

Q. If I want to take Vitamin C to fight a cold, when should I start taking It?

A. There have been no recent long term studies that definitively prove that megadoses of vitamin C lessen cold intensity or prevent colds altogether. But it is accepted that vitamin C enhances the actions of the immune system, helping to fight off foreign invaders and infectious diseases. It stimulates the action and production of antibodies and other immune cells. Studies have shown that adults who received 1000 mg of vitamin C a day showed greater immune cell action. A recent study done in December of 1999 demonstrated a modest benefit in reducing cold duration from ingesting high doses of vitamin C (1000mg), but no evidence that vitamin C prevented colds was seen. Therefore, it would be reasonable to take a supplement that provides the recommended daily allowance every day, and when cold symptoms start, one could increase vitamin C intake to 1000mg a day for the duration of the cold.

Q. I live in a climate that is very cold in the winter and I don’t get outside often. Should I supplement my vitamins in the winter to counteract the lack of sunshine I get?

A. Vitamin D is am important vitamin that is involved in helping the body absorb and effectively utilize calcium and phosphorus and may be important in lowering the incidence of certain types of cancer, although more studies are necessary to determine its efficacy in cancer prevention. Most vitamin D is synthesized by the skin when it is exposed to adequate levels of sunshine. The ability of the skin to manufacture vitamin D is dependent on several factors: age, geography, use of sunscreen, and natural skin pigmentation. People who are older than 50 usually do not produce enough vitamin D from sunlight. These people might want to take a supplement (400 international units) to ensure they get enough vitamin D. In addition, those who live in northern latitudes who are exposed to the sun for less than 15 minutes a day may also benefit from a supplement. The use of sunscreen also prevents sunlight from reaching the skin, reducing the amount of vitamin D that is synthesized. People with increased skin pigmentation also may not synthesize as much vitamin D as their lighter-skinned counterparts. Along with drinking vitamin D enriched milk, a person who lives in the northern latitudes where the sunlight is not as intense would most likely benefit from at least 400 iu of vitamin D as a daily supplement. No one should take more than 2000 iu of vitamin D a day as that could lead to toxicity, with symptoms such as such as nausea, anorexia, and possible damage to the kidneys and cardiovascular system. Good dietary sources of vitamin D include eggs, liver, salmon, and tuna. Make sure to take in adequate calcium along with the vitamin D supplement. With no complicating circumstances, the recommended daily allowance of vitamin D is 200 international units for people 1-50 years old, 400 IU for those between 51 and 70, and 600 IU for those over 70 years of age.

Q. Why does everyone say that getting vitamins from real foods is better than from pills? Don’t the ingredients in the pills come from natural sources?

A. Bodily processes are complex. Every time food is ingested, receptors in the digestive tract signal the release of enzymes that act to effectively absorb and utilize the nutrients. Some of these receptors react to fat, some to carbohydrates or to protein; in short, all these receptors spring into action when a well-balanced meal is consumed. Taking vitamins can be important, but the body most effectively utilizes nutrients when they are contained in food products, since that is when the full digestive enzymatic powers of the gastrointestinal system are put into play. In addition, most vitamins and minerals are digested and used more effectively in combination with other nutrients, and some supplements may not contain the variety of nutrients that food products do. Finally, even with the best intentions, it is difficult to remember to take vitamin pills every morning, but one usually has no problem remembering to eat everyday. Thus, eating a well-balanced diet is a more reliable way of ensuring one’s nutritional needs are met daily. It is a good idea to talk with one’s doctor about the need for vitamin or mineral supplementation, especially if one is anemic, has absorption problems, is pregnant, or has other medical conditions.

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