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Dear Doctor: Selenium

Can you tell me about the supplement selenium. I have Crohn’s disease and someone recommended it. How do you know if you arelacking in selenium?

Selenium is a trace mineral found in soil, water and some foods which our bodies need for normal growth and health.

Certain disorders such as Crohn’s disease and other malabsorptive conditions can cause a decrease in the absorption of selenium, which may result in a deficiency of this essential element. People who are fed intravenously are also at risk of low selenium.

Doctors sometimes suggest that people with these conditions use selenium supplements. Selenium levels can be checked with a blood test, though this is not routinely available.

Can you only take selenium as a supplement or how else can you replace it?

Other sources of selenium are available from foods such as seafood, liver, kidney, lean red meat and grains grown in selenium-rich soil. Other good natural food sources of selenium include nuts, such as Brazil nuts and walnuts, brewer's yeast and wheat germ. Whole foods are the best sources of selenium as it can be destroyed during processing.

If you take supplements the recommended dose of selenium for an adult female is 55mcg/day. This includes the total amount of selenium from your diet and from any supplements. We only need a very small amount — two Brazil nuts a day would contain sufficient amount of selenium for most people. Some forms of selenium supplements, such as organic L+ selenomethionine, may have better bioavailability than selenite and selenate.

What can happen if you take too much selenium — is it harmful?

Yes, symptoms of selenium toxicity include diarrhoea, hair loss, a garlic smell on the breath and sweat, brittle or thick fingernails, nausea and vomiting, or unusual tiredness/weakness, and thyroid dysfunction. Other symptoms include irritability, itchy skin, or a skin rash.

These can be features of other conditions, so always consult your doctor.

I read that selenium can prevent cancer. Is it true?

The role of selenium in cancer prevention has been the subject of recent studies. A recent trial in America suggests that selenium supplementation reduces the risk of prostate cancer among men with normal baseline PSA levels and low selenium blood levels. The dose of selenium used was 200mcg daily. However, this study showed that selenium did not reduce the risk of lung, colorectal, or basal cell carcinoma of the skin and increased the risk of squamous skin cell carcinoma.

Ongoing research is looking in more detail at the role of selenium in prostate cancer prevention.

This advice is to help you make informed decisions about your health. Not all the advice may be suitable if you are pregnant or breastfeeding. Always consult your doctor. Our health advisers won’t enter into personal correspondence.