Ask the experts: Selenium

Q: "What's the story with selenium? I'm always hearing we don't have enough in our soils. Do I need it, and if so, how can I get it?"

A: Nutritionist Claire Turnbull answers:

"Selenium is an essential trace element. This means it is essential to include selenium in your diet as your body doesn't make it on its own. Having too little selenium may result in a reduced protection from cancer and cardiovascular disease as well as compromised thyroid function.

There is a strong focus on selenium in New Zealand because there is huge variability in the amount of selenium in our soils with many being very low. As soil is the growth medium for so many things we eat, in turn our food may be low in selenium compared to other countries.

The recommended dietary intake (RDI) of selenium for adults is 60mcg/day for women and 70mcg/day for men. More than 400mcg/day is not advisable as too much can be toxic.

Good sources of selenium in NZ are seafood, poultry, eggs and some nuts. The amount found in grains (eg. wheat, rye etc) will vary depending on the soil where it has been grown. Brazil nuts are particularly high in selenium and research from Otago University has shown that eating just two Brazil nuts a day is an effective way to increase our selenium levels.  More than that is not advised; it would only take eight each day to deliver an amount which could be harmful (and this doesn't take into account selenium from other sources)."