Selenium was discovered in 1817 by a Swedish chemist called Jöns Jacob Berzelius.
It is similar to tellurium, which had been discovered in 1782 and named after the Latin word for earth 'tellus'. Berzelius kept the celestial theme going and named his new discovery selenium, after 'selene, the Greek name for the moon.
Selenium (chemical symbol Se) is now used as a glass dye, in fireworks to produce red smoke and as an antifungal agent in dandruff shampoos. It was the selenium sulphide in shampoo that killed the alien in the 2001 film Evolution.
In nutrition, selenium is described as an essential trace element, which means we only need a tiny amount of it in our diet, but that small amount is absolutely crucial. The Royal Society of Chemistry says that while our bodies only contain around 14 milligrams (0.014 grams) of selenium, every single cell in our body contains more than a million selenium atoms.
It plays a number of important roles in the body involving the immune system, thyroid function and reproduction and helps to form protective antioxidants which can prevent damage to cells and tissues.
People with higher selenium levels appear less likely to suffer from certain cancers. However, there is no convincing evidence that selenium supplements can prevent cancer and it may be that healthy eating is the key to reducing your risk.
Selenium deficiency can increase the risk of infection and disease and is linked to a number of neurodegenerative diseases, such as Alzheimer's and Parkinson's disease, and mood changes, cardiovascular disease and cancer.
Deficiency has also been linked to reproductive problems, including male and female infertility, miscarriage, preeclampsia, foetal growth restriction (undersized unborn baby), premature labour, gestational diabetes and obstetric cholestasis (a liver disorder that can occur in pregnancy).
The recommended daily amount of selenium for adults is 75 micrograms for men and 60 micrograms for women, and as below for specific ages:
Age Selenium micrograms per day
0-3 months 10
4-6 months 13
7-9 months 10
10-12 months 10
1-3 years 15
4-6 years 20
7-10 years 30
11-14 years 45
15-18 years 70
15-18 years 60
*Department of Health (1991) Dietary reference values of food energy and nutrients for the United Kingdom.
Selenium in food
Selenium is unevenly distributed in the earth’s soil as a result of ancient volcanic eruptions. Because of this, intake varies widely around the world, which makes it difficult to produce accurate food tables that show how much selenium different foods contain.
In parts of Europe, selenium levels in the soil can be low so farmed animals are often fed supplements so that their meat and milk will contain it - in the same way that vitamin B12 supplements are given to animals.
However, surveys indicate that the average UK adult’s intake is 48 micrograms a day, lower than the recommended amount. So meat and milk are obviously not providing enough as most people still consume these.
If you're concerned, you could cut out the middleman, avoid meat and dairy and take your own supplement, or just include more nuts and wholegrains in your diet. The NHS says that if you eat nuts, you should be able to get all the selenium you need from your daily diet.
Food (100g) Selenium (micrograms)
RNI: 60 micrograms for women and 75 micrograms for men
Brazil nuts 254
Sunflower seeds 49*
Green or brown lentils, dried, boiled 40
Cashew nuts, roasted and salted 34
Pecan nuts 12
Mushrooms, fried in corn oil 12
Wholemeal bread, toasted 11
Wholemeal spaghetti, boiled 6*
Red kidney beans, canned 6
Mung beans, boiled 5
Brown rice, boiled 4
Soya milk 4
The selenium content of selected foods
Source: Food Standards Agency, 2002. *Estimated value
Although selenium can be found in meat, fish and eggs, these foods also contain undesirable substances, including saturated animal fat and hormones while fish tend to be contaminated with toxic pollutants.
The richest plant sources of selenium are cereals, grains and Brazil nuts, which can contain very high amounts of 68-91 micrograms per nut, according to the US National Institutes of Health, and too many of those could cause you to go over the upper limit. Fruit and vegetables also provide small amounts of selenium.
Researchers from the University of Otago in New Zealand found that consuming just two Brazil nuts a day for 12 weeks increased the amount of selenium in the blood by over 60 per cent. They said that including Brazil nuts in the diet could avoid the need for supplements.
Nuts are a healthy, nutritious food that provide an excellent source of vitamin E and magnesium. People who eat nuts have higher intakes of folate, beta-carotene, vitamin K, calcium, phosphorus, copper, selenium, potassium and zinc.
Nuts provide valuable phytochemicals and their antioxidant power is similar to that of broccoli and tomatoes. Eating a generous handful of mixed nuts a day - about 42 grams can reduce the risk of heart disease.
But how much selenium you eat is just part of the story; older age, alcohol and smoking are all associated with lower levels, suggesting that these factors may affect how well you absorb and store selenium. One study found that coffee, dairy products, eggs and white rice were all linked to lower levels while bread was linked to higher levels. It seems a wholegrain diet offers the most benefit - again!
Hair, skin and nail supplements commonly contain selenium in levels as high as 100 micrograms and more. However, too much selenium can lead to a condition called selenosis, which can result in nausea, fatigue, garlic breathe and the loss of hair, skin and nails!
In extreme cases, it can result in cirrhosis of the liver, pulmonary oedema and death. Recent evidence suggests too much selenium may also increase cholesterol levels. The NHS says that taking 350 micrograms or less a day of selenium supplements is unlikely to cause any harm.
However, one study found that 200 micrograms a day of selenium supplements increased the risk of aggressive prostate cancer among men with high selenium levels. So concerned were the researchers that they stopped the trial three years early.
They suggest that men over 55 should avoid taking selenium (and vitamin E) supplements at doses that exceed the recommended dietary intake. Another study found that people taking 200 micrograms of selenium a day had a higher risk of non-melanoma skin cancer. These negative effects of supplements appear greatest in those who already have high selenium levels in their blood.
Wholegrains, fruit, and vegetables
The belief that selenium can fight cancer and other diseases has boosted demand for supplements despite a lack of definitive evidence. For selenium, there’s a fairly narrow range between sufficient intake and toxicity.
The recommended amount is 60-75 micrograms a day and the UK’s Expert Group on Vitamins and Minerals set a safe upper limit for selenium at 450 micrograms a day. A quick search on the internet reveals that many supplements contain 100-200 micrograms of selenium; you can see how easy it would be to take too much.
The best way to get your full range of vitamins and minerals is to eat a healthy, balanced diet with a wide variety of wholegrains, fruit and vegetables. If you are going to take supplements, stick to the recommended intake.
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This article wasoriginally published by Viva! Health here