香蕉视频

There is a lot of buzz around a set of scientific papers that calls into question the effectiveness of multivitamin supplements. Let me add a few notes to the buzz as the vitamin supplement industry licks its wounds and scrambles to protect the goose that lays its golden egg. And it鈥檚 a valuable egg. Consumers in North America fork out close to fifteen billion dollars a year on vitamin and听mineral supplements. Why? Some have heard that our soil is depleted in nutrients and that our food supply no longer provides adequate amounts of vitamins and minerals. Not so. Modern fertilizers supply the nutrients crops need, otherwise they would not grow properly. Others buoyed by an onslaught of exuberant claims cranked out by the supplement industry aim to slow down age associated mental decline as they fend off ailments such as heart disease, cancer and diabetes.

There is of course no doubt that vitamin deficiency can lead to medical problems. A lack of vitamin C will cause scurvy, inadequate intake of niacin leads to pellagra and osteoporosis ensues when there is a lack of vitamin D. But when it comes to chronic diseases, the situation becomes more complicated. People who eat lots of fruits and vegetables tend to be healthier, and the general assumption has been that vitamins in these foods play a role. However, studies using vitamin supplements have not supported this assumption. In one widely publicized case, raising vitamin A levels in smokers through supplementation with beta-carotene, the body鈥檚 precursor for the vitamin, actually increased the risk of lung cancer! Now three papers published in the Annals of Internal Medicine, a top notch journal, have thrown another wrench into the works. An accompanying editorial delivers the message very clearly with the provocative headline, 鈥淓nough is enough: Stop Wasting Money on Vitamin and Mineral Supplements.鈥� That鈥檚 the kind of headline in a medical journal that may put supplement promoters at risk for a heart attack.

Heart attack risk is exactly what is addressed by one of the supplement studies. And it wasn鈥檛 a small study. 1708 patients who suffered a heart attack were asked either to take a daily high-dose multivitamin, multimineral supplement or a placebo. Over roughly a three year period there was no difference between the groups in the incidence of a cardiovascular event. The researchers did note, though, that about half of the participants either did not take their assigned pills regularly or withdrew from the study. A second paper examined the role of supplements in preventing heart disease or cancer. The researchers reviewed a total of 27 studies involving 400,000 participants and concluded that no benefits could be attributed to supplements. What about the possibility of improved mental function? That was evaluated in a study of close to 6000 physicians over the age of 65, half of whom took a multivitamin supplement and half took a placebo for 12 years. There was no difference in overall cognitive performance or verbal memory. It is also noteworthy that since 1990 there has been a 33% increase in the use of multivitamin supplements among adults in North America without any observable benefit.

Will these papers in the Annals of Internal Medicine slam the door on the vitamin supplement question? No. Every study can be criticized. For example, in the one assessing mental decline, the subjects were physicians who were well nourished. Could the results have been different if they had a poor, nutrient deficient diet? Maybe. Supplement promoters claim that surveys show many people have diets that contain less than the recommended daily intake of vitamins? Would a supplement that costs a few pennies a day not be worth it as nutritional insurance? What I would ask is why 400,000 people, who pretty well represent a cross-section of the population, would not see any dividends paid out. Surely, they did not all have a well-balanced diet, whatever that might mean.

In some cases vitamin supplements are indicated. Folic acid taken by pregnant women reduces the risk of birth defects and people with various malabsorption problems benefit from vitamin supplements. In the developing world vitamin A deficiency is rampant, mostly because a diet restricted to rice does not provide adeqauet amounts of beta carotene, the body鈥檚 precursor for vitamin A. Here, vitamin A supplements could mean the difference between life and death. But for the majority of the population in the developed world, the most active ingredient in vitamin supplements is not listed on the label. It is hope! While it may not make people better, it can make them feel better. And that鈥檚 something. But at the same time we should bare in mind that grandiose claims about vitamin supplements preventing major diseases are not borne out by the evidence, as is once again demonstrated in this trio of impactive papers published in the Annals if Internal Medicine, which is several steps above the National Enquirer鈥�

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