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The Science Behind Selenium
Selenium is a trace mineral found in soil and food. It is used by the body to regulate thyroid function and helps to make antioxidant enzymes which prevent cell damage. Like other antioxidants such as vitamins A, C, E and quercetin, it keeps nasty free radicals at bay.
Some studies show that selenium can help prevent certain cancers and cardiovascular disease. It also protects the body from the poisonous effects of heavy metals and other toxins – like the ‘bad halogens’ and mercury vapour release from amalgam fillings when we chew.
As explained in Chapter 5 of Mad Diet, the thyroid assists in weight management by releasing hormones that control our metabolism. Therefore, nutrients that help our thyroid function properly, such as iodine and selenium, are essential for maintaining healthy weight.
People who live in areas where there is very little selenium in the soil have a higher risk of becoming deficient. In the UK levels are very low as melting ice caps washed selenium from British soils 10,000 years ago and what little was left has been further depleted by intensive farming.
Right up until the 1980s most of the bread in the UK, a big part of our diet, was made with American wheat grown in soil naturally high in selenium. But when a major change in land use occurred during the 1980s many British farmers switched from growing barley to growing wheat so our selenium levels started to plummet.
Another key factor in British selenium deficiency is that by the end of the 1980s we were no longer eating offal, which is especially high in selenium. As a result, the British diet now only contains 50 per cent of the RDA of selenium which should be around 70 micrograms per day.
There are many studies linking selenium deficiency to mental health problems. A study conducted by the University of Otago and published in the prestigious Journal of Nutrition in 2014 showed a strong link between selenium concentration and depressive symptoms and negative mood. Another review of five studies published in Nutritional Neuroscience showed that low-dietary selenium was clearly linked to poor mood and depression. And other studies have shown that selenium supplementation has proven effective for treating postnatal depression.
Foods naturally high in selenium include: Brazil nuts – with a whopping 1917 micrograms per 100 grams – just a small handful of Brazil nuts is more than plenty to ensure you get your daily allowance. Offal meat is also high in selenium. Oysters, tuna, wholewheat bread (if the wheat is grown in selenium-rich soil), fish and organic poultry are also good sources of this trace mineral.
A report compiled by researchers at the Rowett Institute of Nutrition and Health at the University of Aberdeen states that the current average selenium intake in the UK is around 29 – 39 micrograms per day – half of the recommended daily allowance. The Rowett Institute report also states that, “The human body can tolerate quite high levels of selenium without adverse effects on health. However high doses of over 900 micrograms per day can elicit toxic effects.”
Health store selenium supplements usually come in 200 microgram (µg) capsules, so unless you are going crazy on the Brazil nuts, or eating liver and kidneys for breakfast, lunch and dinner, it is safe to say a supplement of 200 micrograms is well below the upper tolerance level and safe to take. This is true despite it being higher than the RDA.
Remember there is a growing body of evidence to suggest many of the accepted RDAs are set too low – sometimes far too low.