Our selenium deficiency

by Jennifer Bowden / 16 June, 2012
Some 45% of adults have an inadequate selenium intake, a national survey has shown.

Question: You have written previously that broccoli contains certain minerals, such as selenium. As New Zealand soil is defi cient in this mineral, can broccoli take up much if there are only traces in the soil? What other plants take up selenium? I eat a good balanced diet, but am I wasting my money taking a 100mcg selenium tablet each day?

Answer: Selenium intake varies tremendously around the world, from regions in China where severe deficiencies cause Keshan disease, through to places where selenium levels are so high that toxic concentrations accumulate in the population, causing garlic breath, hair and nail loss, disorders of the nervous system and skin, poor dental health and paralysis. New Zealand soil is low in selenium, so crops grown here have lower levels than their overseas equivalents, which leads to lower levels of this mineral throughout our food system and a population with a marginal selenium status.

The 2008/09 New Zealand National Nutrition Survey found that although selenium intakes had increased since the previous survey in 1997, 45% of adults still have an inadequate intake. Those most likely to have a low selenium intake were adults 70 years and over, and girls aged 15-18, of whom 70% had an inadequate intake. These are worrying statistics, as low selenium status is associated with an increased risk of mortality, poor immune function and cognitive decline, according to a recent review in the Lancet.

Selenium has many important roles in our body, from antioxidant and anti-inflammatory effects to production of thyroid hormones. Higher selenium status or selenium supplementation has antiviral effects, reduces the risk of autoimmune thyroid disease and is required for successful reproduction. Observational studies have also noted that higher selenium status is associated with a reduced risk of prostate, lung, colorectal and bladder cancers. Clinical trials of selenium supplementation have not demonstrated such a result, leading researchers to conclude that supplements may only benefit people with inadequate selenium status.

Indeed, evidence suggests that if people with an already adequate selenium status take supplements, they may increase their risk of developing Type 2 diabetes. As with many nutrients, there is a U-shaped relationship between selenium intake and human health; that is, there is a higher risk of adverse health effects with both a low selenium status and a higher status. So the crucial point is that although supplements may benefi t people with low selenium status, those supplements may harm people who have an adequate-to-high status, according to the 2012 Lancet review.

The best advice, as always, is to meet all our nutritional needs through diet. Fish, other seafood, poultry, meat, eggs and bread are rich sources of selenium, with bread the largest single contributor to our diet. The recent introduction of high-selenium Australian wheat and other imported wheat into North Island bread has significantly improved our selenium status. Although the selenium content in plant foods depends on soil levels, some plants, including garlic, onion, broccoli and wild leek, are able to accumulate selenium from soil. Hence New Zealand-grown broccoli typically contains 0.5mcg of selenium per cup, whereas the same quantity of cabbage or brussels sprouts contains just 0.1mcg.

Brazil nuts – the richest known source of selenium – also accumulate it from the soil. Selenium supplements aren’t recommended unless taken under a doctor’s supervision, because high intakes can be toxic and harm your health. A safe and effective way to improve your selenium level is to add a couple of brazil nuts to your daily diet. A 2008 New Zealand study, published in the American Journal of Clinical Nutrition, found that eating two brazil nuts daily was as effective at increasing selenium status as a 100mcg supplement. What’s more, they’re a tasty solution.

Email: nutrition@listener.co.nz, or write to “Nutrition”, c/o Listener, PO Box 90783, Victoria St West, Auckland 1142.


China could be using Taiwan as a testing ground for disinformation campaigns
102550 2019-02-20 00:00:00Z World

China could be using Taiwan as a testing ground fo…

by Gavin Ellis

A Taiwanese diplomat’s death in Japan has become a symbol of the consequences and dangers of disinformation.

Read more
The best way to beat food cravings? Fill up on the objects of your desire
102087 2019-02-20 00:00:00Z Nutrition

The best way to beat food cravings? Fill up on the…

by Jennifer Bowden

Research has shown that dieters’ attempts to resist eating certain foods appear to lead to cravings for those foods.

Read more
Deepfake: How disinformation fools our brains and damages democracy
102545 2019-02-20 00:00:00Z Tech

Deepfake: How disinformation fools our brains and…

by Gavin Ellis

Message manipulation using bots, algorithms and, now, AI software is making it harder to know what’s real – and threatening democracy itself.

Read more
Move to introduce digital tax for foreign companies profiting online
102519 2019-02-19 09:23:12Z Economy

Move to introduce digital tax for foreign companie…

by RNZ

New Zealand is lining up to introduce a new tax on multinational companies that make money out of online goods and services in this country.

Read more
National's high-risk gamble on marijuana and euthanasia
102484 2019-02-19 00:00:00Z Politics

National's high-risk gamble on marijuana and eutha…

by Graham Adams

Having polarising MPs like Paula Bennett and Maggie Barry leading the opposition to popular reforms could be kryptonite to the National Party.

Read more
Reflections on my encounter with the charming Dan Mallory
102482 2019-02-19 00:00:00Z Profiles

Reflections on my encounter with the charming Dan…

by Michele Hewitson

He penned a bestselling thriller, but as Michele Hewitson discovered, author Dan Mallory also proved himself to be a charmingly adept bullshit artist.

Read more
Sounds of summer: Notable Kiwis name their favourite summer songs
102500 2019-02-19 00:00:00Z Music

Sounds of summer: Notable Kiwis name their favouri…

by Phil Gifford

How music can transport you back to your most memorable summer.

Read more
Inside the close-knit community that lives along the Cromwell-Tarras Rd
102505 2019-02-19 00:00:00Z Travel

Inside the close-knit community that lives along t…

by Mike White

Mike White heads up the Cromwell-Tarras road to merino and wine country.

Read more