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One brazil nut a day is enough to raise the average New Zealander's selenium intake to internationally recommended levels and eating two could lead to added health benefits, new research shows.

However, Otago University researchers warn that too much of the micronutrient can be toxic and people should be careful to limit themselves to no more than a few nuts a day.

Department of Human Nutrition Professor Christine Thomson said today the nuts were a simple, effective and relatively low-cost way for people to boost their levels of the essential micronutrient.

New Zealanders have a marginal selenium level compared to many other Western countries, owing to soils here being generally low in the mineral.

"There is mounting evidence that a marginal selenium status can lead to an increased risk for a range of conditions, including cancer and cardiovascular disease," Prof Thomson said.

There was growing scientific support that higher intakes might provide additional health benefits, like enhancing the body's immune system.

Prof Thomson and colleagues carried out the first-ever study to look at how much selenium people can obtain from brazil nuts and the resulting levels of antioxidant activity in their blood.

Their study appeared recently in the American Clinical Journal of Nutrition.

Sixty volunteers were tested over 12 weeks. They were divided into three groups, one of which ate two brazil nuts a day, while the other groups were given either a 100 microgram selenium supplement or a placebo to take daily.

The results showed the blood selenium concentrations of the brazil nut group were up by 64.2 per cent, the selenium supplement group's increase was 61 per cent and the placebo group 5.3 per cent.

The results showed that including a couple of brazil nuts a day in the diet could ensure a greatly enhanced selenium status without needing to fortify other foods or take supplements.

Prof Thomson said that while New Zealanders' low selenium intakes needed addressing, too much of the micronutrient could be toxic.

"People should be careful to limit themselves to no more than a few brazil nuts per day, otherwise selenium could potentially accumulate to toxic levels in body tissues."