Selenium

With huge thanks to Naomi Leppitt for her help with this post.

What does it do and why do we need it? 

Selenium is used in the body to make antioxidants that work with iodine to make the thyroid hormones. These help our body regulate metabolism, immunity and growth. For example they can control how powerful a
virus is, help stop HIV progressing to AIDs, and reduce the risk of dying
from some cancers (Rayman, 2000, 2012).

Selenium also helps with cognitive function and plays an important role in fertility plus it is a key nutrient during pregnancy.


In men, selenium is used to create testosterone and to make sperm, so it’s an important nutrient for fertility and family planning. Animal studies have shown that deficiency in a selenium can make an animal infertile and human studies also show that selenium levels tend to be lower in infertile men. A trial giving men with reduced fertility, 100mcg selenium per day for 3 months significantly improved sperm motility, and 11% of men became fathers (Scott et al 1998).

In women, low selenium levels are linked to a higher likelihood of miscarriage and pre-eclampsia (Rayman, 2000, 2014).


How much do I need? 


In the UK, women need 60mcg/day and men 75mcg/day.
Unfortunately, UK average intakes are below this, nearer 39mcg/d. This has decreased since the 1960’s, when we were meeting our selenium targets and that is likely due to a shift in where we get our flour imported from.


Where can I get it? 

So we have establised that Selenium is an important nutrient and we probably need to be eating more of it. Whilst it may seem easy to just take a supplement it is always best to get nutrients from a food source when you can. Nutrients all interact together and it can be easy to overdose on certain micronutrients.


Selenium is found in soil, where it is passed to foods grown in that soil and to animals who eat the soil. Rich foods that can contain selenium are: fish and seafood, meat and poultry, cereals and grains, milk and dairy
products, eggs and nuts.

If you are eating a plant based diet, vegetarian or vegan then you are more likely to not to be getting enough selenium because plant sources
of selenium are less-rich in selenium.

Here are a variety of foods and their selenium content. Have a think about what you eat and see if you’re meeting the guideline:

  • Mushrooms ½ cup 10-20 mcg
  • Pasta ½ cup 20mcg
  • Rice ½ cup 10mcg
  • Yoghurt, greek ¾ cup, 175g 15mcg
  • Milk 250ml, 1 cup 8-10mcg
  • Cottage Cheese 250ml, 1 cup 15-30mcg
  • Fish 75g 15-65mcg
  • Chicken, Pork, Beef, Lamb 75g 15-40mcg
  • Baked beans 175ml, ¾ cup 20mcg
  • Mixed nuts 60g, ¼ cup 50-154mcg
  • Seeds (sunflower / chia) 60g, ¼ cup 30mcg
  • 5 x Brazil nuts 350mcg
  • 2 large Eggs 35mcg


What happens if I don’t get enough selenium in my diet? 

If you’re deficient in selenium, it may affect how your brain works, affecting your memory, concentration and decision making. It can also impact your immune system and how well you fight off viral infections. Low selenium can affect your fertility and ability to conceive a child. Selenium deficiency can also increase risk of some cancers, cause
thyroid disease and even increase the risk of death! This all sounds pretty scary but by eating selenium rich foods you can meet your needs.

How much is too much?


You don’t need a lot. 3 brazil nuts a day should be the limit: more than that and you risk toxicity.

When you have excess selenium in your system, you can develop the condition selenosis – shown by hair loss and nail loss, and garlic-smelling breath!

References:

  • Lectures by Prof Margaret Rayman, DPhil.
  • Lemire M et al 2012 No evidence of selenosis from a selenium-rich diet in the Brazilian Amazon, Environment International, Volume 40:128-136
  • https://www.dietitians.ca/Downloads/Factsheets/Food-Sources-of-Selenium.aspx
  • Rayman MP 2000, The importance of selenium to human health. Lancet. Jul 15;356(9225):233-41.
  • Rayman MP 2014 Effect of selenium on markers of risk of pre-eclampsia in UK pregnant women: a randomised, controlled pilot trial. Br J Nutr 112:99-111
  • Rayman 2012 Selenium and Human Health Lancet; 379:1256-1268
    Scott R et al, 1998 The effect of oral selenium supplementation on human sperm motility. Br J Urol. Jul; 82(1):76-80.
  • Serving sizes of selenium: https://www.dietitians.ca/Downloads/Factsheets/Food-Sources-
    of-Selenium.aspx
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