Selenium is one of those substances we need only little of, but without any at all, we die.
Our bodies don’t produce it – we have to eat it – but there are serious concerns being raised in scientific circles because the amount of selenium present in our soil and food supply has fallen.
We obtain most of our selenium from meat and poultry, which in turn relies upon selenium being present in animal feed and forage. However, selenium deficiency is now routinely diagnosed in UK cattle, and the failure to supplement animals or soil accelerates a deficiency in our own diet.
So what exactly are the benefits of selenium for us humans? I asked Dr Margaret Rayman from the University of Surrey for an insight into the chemistry involved. Dr Rayman explained that inorganic selenium is picked up from the soil by plants and converted to organic forms such as selenomethionine which can be readily absorbed and utilised by humans and animals. Once we eat an organic form, we manufacture important enzymes called selenoproteins.
Selenoproteins protect our cell membranes from oxidising free radicals – these are highly damaging molecules responsible for aging and disease. Antioxidant protection from selenoproteins helps the body defend itself against pollution, poor diets and smoking. Selenium is also crucial for thyroid hormone production. Other benefits of selenium include reduction of inflammation, DNA synthesis, fertility and reproduction. Finally, selenium forms a permanent bond with some heavy metals, including mercury, inhibiting their harmful effects.
Dr Rayman confirmed the worrying statistic that selenium levels in the UK have fallen by 50% in the last 50 years and are now well below the recommended 75 mcg/day for males and 60 mcg/day for women. Now, our average intake is only around 29-39 mcg per day. Aggressive farming, the over-use of fertilisers and acid rain have all contributed to selenium depletion, and there is no co-ordinated effort to improve matters in sight.
Should we be concerned about ever-decreasing selenium levels? According to Dr Rayman, the latest research shows that lowered levels may affect immunity and increase the risk of certain cancers, miscarriage and pre-eclampsia. It all depends on our individual genetic makeup, which determines our ability to turn selenium into protective selenoproteins. By taking extra selenium, we may counteract any difficulties in making those precious selenoproteins.
Those particularly at risk of selenium deficiency include vegetarians, the elderly, pregnant and nursing mothers and smokers. There is also some evidence that people with arthritic disorders may be low in the mineral. If supplementing with selenium, please remember that selenomethionine is the most bioavailable, and don’t exceed 200 mcg per day.
© 2011 Martina Watts MSc Nut Med, First Published Brighton Argus May 2006