"Eat to Live, Not Live to Eat"
John H Weisburger, 2000
Selenium (Se) is an essential micro-nutrient but more than a billion people worldwide, mainly in undeveloped countries but also many parts of Europe, have deficient intakes. The Australian NHMRC recommends a daily intake (RDI) of 70 and 60 mcg/day for adult men and women respectively. In the average Australian diet, most of this comes from two food groups, cereals and meats. These two main groups are not particularly rich in Se but as staples in the diet, sufficient amounts are consumed to add up. Se levels in all foods are greatly influenced by the particular plant species and the soil content. For example in one study, pasta products made from US wheat contained 57mcg/100g Se, whereas an Italian equivalent had only 6mcg/100g. For comparison, Australian sourced pasta has 1-10mcg/100g.
There are many geographic areas worldwide that have low soil Se (some regions in China are extreme), and the south west of WA is one of them. So for example, wheat grown here does not have good Se content. Depending on the makeup and source of individual dietary components, people can become deficient and this may lead to Keshan's disease, compromised reproductive, immune and brain function and decreased resistance to viral infections. The average adult intake in the UK is only 30-40mcg/d. Australians have fared better in the past (57-87mcg/d) but this has been in decline over the last 20 years. Although acute deficiency states are not usually seen here, many recent studies have shown that intakes at or above the RDI can have positive effects on the above-mentioned conditions as well as reducing total cancer incidence and mortality.
How can we ensure we're consuming sufficient to avoid deficiency problems and hopefully also benefit from amelioration of chronic diseases? One broad approach in deficient areas such as Finland, is for the government to mandate that all agricultural fertilizers be supplemented with Se so more is taken up by plants, and these are then richer sources whether subsequently used as human foods or livestock fodder. Unlikely or at least years away for us, given we don't have severe deficiency problems. Tablet supplementation is less than ideal as Se exists in many forms and the availability, action and fate of these in the body varies - which form/s should a tablet contain?
The following study by Yang (LWT- Food Science & Technology, 2009, 42, 1573-1580) makes the case for regularly including brazil nuts in your diet:
Epidemiological studies have shown an inverse relationship between nut intakes and chronic diseases such as cardiovascular diseases and cancers. Brazil nuts contain abundant dietary antioxidants, especially Se. One single Brazil nut provides 160% of the US Recommended Daily Allowance – probably the best source of Se from plant-based foods. Brazil nuts possess phenolics and flavonoids in both free and bound forms and are rich in tocopherol, phytosterols, and squalene. The possible beneficial effects of these compounds are due to their antioxidant and anti-proliferative activities, which are linked to a reduced risk for developing atherosclerosis and cancer.
The NZ population is Se deficient and a 2008 study suggested that two brazil nuts a day could help ensure adequate intake. However as with many nutrients, adequate is good but when taken to excess, toxicity can develop. The NHMRC recommends an upper intake limit of 400mcg/d. While over-zealous use of tablet supplements with the goal of minimising future chronic disease can all too easily occur, this is also the case with brazil nuts, as they can be such a rich source of Se depending on their provenance (average 1920mcg/100g). Accordingly, their consumption should be limited and not gorged.