Suppose that an expert argues that people in the US should take vitamin E supplements because two clinical trials (PPS and Linxian A) have found that vitamin E supplements significantly reduced mortality. Would you find this argument persuasive? ____ Yes ____ No Explain why or why not. When different clinical trials yield different results, researchers can use a statistical technique called meta-analysis to combine the results from the different clinical trials and calculate a best estimate of the true effect based on all the available data. A recent meta-analysis of clinical trial results estimated that the participants who took vitamin E supplements had 3% higher mortality risk than the participants who took placebo. This result provides the best estimate effect of vitamin E supplements on mortality in economically developed countries like the US. If vitamin E supplements do cause a 3% increase in mortality risk, this could be considered a relatively small increase in risk for any individual, but it could add up to a lot of deaths if lots of people are taking vitamin E supplements. In summary, the results from the clinical trials suggest that vitamin E supplements may increase mortality in countries like the US, but may decrease mortality in regions with less adequate diets. To understand how vitamin E could have opposite effects in different circumstances, we need to look at the results from laboratory experiments where researchers tested the effects of vitamin E on molecules or cells in a test tube or petri dish. Laboratory experiments have shown a wide variety of beneficial and harmful effects of vitamin E, including the following. Laboratory experiments have shown that vitamin E can have antioxidant effects which protect molecules and cells from damage. However, under other experimental conditions, vitamin E can have pro-oxidant effects which can harm molecules and cells. Laboratory experiments have also shown that vitamin E can decrease blood clotting. Decreased blood clotting can reduce the risk of some diseases (e.g. heart disease and a type of stroke caused by blood clots which block needed blood flow), but increase the risk of other diseases (e.g. a different type of stroke caused by bleeding in the brain). Thus, vitamin E has multiple effects on the molecules and cells in our bodies, and the balance between beneficial and harmful effects of vitamin E supplements may vary depending on factors such as how much vitamin E people are getting from their diet. Because vitamin E has both beneficial and harmful effects, the results of laboratory studies cannot tell us whether the overall health effect of vitamin E supplements will be beneficial or harmful. An advertisement urges you to take an antioxidant supplement that contains several types of antioxidant molecules that laboratory experiments have shown can prevent damage to other molecules and cells. Before you decide whether to take the antioxidant supplement, what else would you want to know?
