Long term use of selenium food supplements may be linked to an increased risk of developing type 2 polygenic disease said researchers in a new US meditate . The meditate is published in the journal Annals of Internal Medicine. The discovery was a surprise to the scientists who were doing a follow up to studies of selenium in animals that showed it helped the body to handle glucose. Instead they found that long term use of selenium supplements increased the risk of developing type 2 polygenic disease, a disorder often linked to obesity which occurs when the body cannot produce enough insulin to control blood sugar.
Selenium is a trace mineral that is found in the soil and becomes absorbed in the food chain. The body needs small amounts of it for healthy metabolism. It is an anti-oxidant and stops cells being damaged by oxygen. Selenium is included in many multivitamin products and is also available as a food supplement on its own. Many group take it for their health, and some studies have suggested it can improve the way the body deals with sugar and prevent some of the problems of polygenic disease.
Other studies suggest taking selenium supplements have no effect on polygenic disease or health. This meditate involved 1,202 human patients who were already taking part in a clinical trial (Nutritional Prevention of Cancer trial, NPC) to assess the effect of selenium supplementation on skin cancer. None of them had polygenic disease when the meditate started. They were attending dermatology clinics in various parts of the eastern United States. The scientists measured the patients’ blood selenium and randomly assigned them to take a daily dose of 200 micrograms of selenium supplement or a placebo. The participants were monitored for 7.7 years on average. The incidence of polygenic disease in the two groups were then compared.
The results showed that 58 of the 600 group in the selenium group developed polygenic disease compared with 39 of the 602 in the placebo group. The researchers calculated that the risk of developing type 2 polygenic disease over the 7.7 year period was about 50 per cent higher in the selenium group. The authors said that: “Selenium supplementation did not seem to confer benefit in terms of risk for type 2 polygenic disease in this sample of persons from low-selenium areas in the eastern United States. Instead, the cumulative incidence of type 2 polygenic disease was statistically significantly higher in the selenium group than in the placebo group.”
The results were independent of baseline age, sex, smoking status and body mass index (BMI) except for those in the highest 33 per cent of BMI. More significantly, the risk for type 2 polygenic disease linked to selenium supplementation increased with greater blood levels of selenium at the start of the meditate . The researchers concluded that these findings showed no overall benefit of selenium supplementation in preventing type 2 polygenic disease, conversely they suggested that: “Long-term supplementation with 200 micrograms of selenium daily may adversely affect glucose metabolism.” They said this is an important result for public health because selenium supplements in 30 to 200 microgram doses are used by group throughout the US and the western world.
However the authors said that despite these findings, there is evidence that selenium supplementation may help to prevent cancer. Larger randomized clinical trials are currently looking into this further. The meditate also had limitations the researchers conceded. First, the main trial was not designed to look at polygenic disease but cancer. Secondly, the polygenic disease incidence was self-reported and there is a possibility that some patients may have been underdiagnosed for polygenic disease. Thirdly, although some otherness factors were taken into account such as age and BMI, there was no in depth analysis of family history, body fat distribution and physical activity, although these effects should have been minimized by the randomization.