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Vitamins, your opinions please

by Hepth
Tags: opinions, vitamins
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Ygggdrasil
#19
Jun25-14, 01:14 PM
Other Sci
Sci Advisor
P: 1,394
Nature just published a news feature on this topic that discusses this issue, and it echoes advice in this thread that vitamins are probably beneficial if you are deficient in a particular nutrient but are not beneficial (and can in some cases be harmful) if you are not already deficient in that nutrient:

Researchers at the Harvard School of Public Health recruited 672 health professionals with histories of benign colorectal tumours, a risk factor for colorectal cancer, to see if folic acid helped to reduce tumour recurrence. Half of the participants took 1 milligram of folic acid a day for between 3 and 6.5 years, and the other half took a placebo. The supplements had no effect when everyone was analysed together, but among the people with the lowest folic acid intake at the start of the trial, those who took supplements had a reduced risk of recurrence.

On the other side of the coin, several large trials suggest that over-consuming nutrients could be dangerous. The Alpha-Tocopherol Beta-Carotene Cancer Prevention Trial set out to see whether smokers would benefit from certain supplements. It turned out that those who took 20 mg of the vitamin A precursor β-carotene a day — 3 times the US recommended daily allowance for vitamin A — for 5–8 years were, in fact, 18% more likely to develop lung cancer than those taking a placebo. A potential explanation is that the breakdown products of β-carotene can, at high doses, cause cell proliferation.

These results illustrate one of the many complexities of nutrient metabolism. Nutrition scientists now recognize that risk curves are J- or U-shaped: nutrients have beneficial effects at low doses and toxic effects at high doses. The magnitude of the response differs, too, depending on where individuals start on the curve — their baseline status.
The article also discusses how it can be difficult to draw conclusions from the published literature because of many confounding variables in the studies (e.g. problems with self-reporting of diets, compliance with the treatments, and differing baseline intakes of the nutrients among study participants).


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