Selenium is interesting stuff. It's toxic in large quantities, but seems to be essential for cellular life (which means all life.) Too much and you die, too little and life can't exist. It's most closely related to sulfur, and with an atomic number of 34, it's higher on the periodic table than iron, copper, nickle, zinc, etc. Europeans tend to get less of it in their diets than do Americans, because the main source in human diets is grain, which picks it up from the soil. Since there's less in European dirt than in the American variety, there's less selenium in the grains Europeans consume. (I'm not sure about other regions, since the study read only compared America and Europe. I wonder if this might be due to the fact that European soil has been intensively farmed for a far longer period than in North America? If this is the case, you'd expect Asians to suffer a similar shortage, while Australians would be even better off. I've no idea if it's true or not.)
As with vitamin D, it's also one of those things that the more you study it, the more you realize that it plays a really important role in human health. A recent study concludes that selenium plays an important role in prevent bowel cancer, and (I suspect) pretty much all cancers, because
one function [of selenium] is enhancing the triggering of "apoptosis" - a vital process that allows cells to kill themselves if they detect an error. "When a cell realises that something has gone wrong it can trigger its own death so the cell doesn't become a problem," said Prof Young, head of the Flinders Centre for Cancer Prevention and Control at Adelaide's Flinders University. "What the selenium does is just make the cell better at perceiving that it has to kill itself."There is a major down-side though. If you take too much:
"your hair falls our, your nails fall out, you get kidney problems and you can potentially get problems with glucose and insulin control too."Still the study seems to indicate that an increase in the recommended daily dose is warranted, from the current 50 micrograms to about 150 micrograms. What's the best way to get it? Eat four brazil nuts a day. With Christmas coming up, there's never been a better excuse to stock up on nuts.
I'm not into health fads, but next time I'm in the supermarket I'm going to buy a bag.
[Update] I did some digging on selenium levels, and New Zealand has a particular deficiency. That kills stone dead my speculation that it might be to do with intensity of farming, as NZ didn't even have people until (perhaps) a thousand years ago, and intensive farming only in the last couple of centuries. Australian soil is also deficient.
[Further update]. Oh great ... maybe I'll have to hold off on the brazil nuts. Another study has linked the incidence of diabetes to high levels of selenium. They're still recommending people in selenium deficient countries take supplements, but people in the US should just maintain a regular healthy diet. Oh well ... I'm sure cashew nuts must be healthy. I'll have them instead. 
