Food affects mood more than most of us realise, and low selenium levels in the diet can lead to irritability and depression

Food has always played a role in influencing our mood, whether it’s feeling romantic after slurping down oysters, or blissful after munching on chocolate.

And as scientists discussed at the recent London Mood and Food conference – organised by the British Nutrition Foundation – the relationship between the two has been further underlined since the discovery of a link between selenium deficiency and depression.

According to scientists from the Department of Psychology at the University of Wales in Swansea, a deficiency in selenium – an essential trace element found in cereal grains, meat and fish – may be associated with increased anxiety, depression and fatigue.

It also acts as an antioxidant and can help the body to fight cancer and heart disease. The current average adult intake of selenium for women and men is thought to be around 43 micrograms (mcg) per day. This compares unfavourably with the government’s recommended daily intake of 75mcg for men and 60mcg per day for women.

Selenium is found in varying concentrations in soils throughout the world. While levels are high in North American soil, they are comparatively low in Britain and Europe. Due to a decrease in imports of selenium-rich, high-protein wheat flour from North America and Canada, and an increase in the acquisition of locally produced wheat, daily selenium intake among the British population fell dramatically from 60mcg in 1978 to around 43mcg by the 1990s.

The Food Standards Agency, which looks at trends in food consumption, noted in its annual National Food Survey that there has been a decrease in bread consumption over the past 10 years. This is also believed to be a cause in the reduced intake of selenium. Finally, the low bio-availability (i.e. the amount that the body is able to use) of this mineral in soils due to acid rain and excessive use of artificial fertilizers, has also affected selenium intake.

The study published in Biological Psychiatry in 1991 by doctors David Benton and Richard Cook at the University of Wales, was designed with the aim of examining the impact of selenium on moods.

While previous studies have looked at selenium deficiency in relation to the concentration of the mineral in red blood cells, kidney, liver and testes, its presence in the brain has always been ignored.

The Benton and Cook study was ground-breaking because it was the first time researchers considered the possibility that low selenium levels may have psychological consequences.

The 50 subjects who took part were either given a daily placebo or a 100mcg selenium supplement over a five-week period. They were then asked to monitor their feelings and moods, and which foods they had eaten – in order for the researchers to estimate their overall daily intake of selenium.

The results showed that the lower the level of selenium in the diet, the more the subjects reported feelings of anxiety, depression and fatigue. The results also showed that these feelings subsided following the addition of selenium supplements to the diet.

However, before you rush off to the nearest chemist to buy selenium supplements, be aware that overdoing it can be bad for your health. In 1991, the Department of Health reviewed the daily amounts of minerals necessary for an average person. It found that excessive doses of selenium – over 3.2 milligrams (3200 mcg) per day – were toxic and could lead to neurological abnormalities, dry, brittle hair or hair loss, and, in severe cases, paralysis.

So, in fact, supplementing a diet that already provides adequate amounts of selenium may not be beneficial. However, if you aim to eat a balanced diet of carbohydrates, a couple of portions of protein from meat or fish, the usual 5 portions of fruit and veg and a couple of portions of milk and dairy products every day, you should be getting sufficient amounts of selenium to put you in a positive frame of mind.