Selenium: The valuable mineral you can have too much of.
Posted Apr 24 2012 10:16pm
Can you have too much of a good thing? It seems that our modern diets are deficient in valuable minerals, partly due to what we choose to eat, and also from modern agricultural practices. And yet selenium is unique as a mineral you need to be careful with when supplementing, because it can build up in your body. The toxicity of selenium has been known since horses in certain parts of China and the USA became fatally ill, after a long period of eating grains grown in soil with a very high selenium content.
Actually, selenium is a difficult mineral to pin down in lots of ways. How much selenium is contained in your food depends on how much was in the animal, or the soil the plant you ate was grown in. Some foods, particularly Brazil nuts and brassica vegetables (garlic, onion and broccoli) can accumulate selenium. Brazil nuts harvested in different parts of Brazil have been found to contain up to 10 times more selenium, simply due to the different selenium content of the soil. To complicate matters, the biochemical process your body uses to absorb selenium, although efficient, is still unclear. There are different forms of selenium too, which can affect how much is absorbed from your food.
If you take in too much selenium (only likely if you take too much as supplements) you can experience symptoms of toxicity, as your body will continually accumulate it. Because of this, there are often warnings on supplements containing selenium, that list the safe upper limit for dosing.
Although it can be dangerous in large quantities, it’s still a valuable nutrient. Selenium acts as an antioxidant, actively helping slow the ageing process by soaking up free radicals, and promoting healthier DNA reproduction in cell division. Selenium is also part of the enzyme that helps convert your thyroid hormones to their active form; this helps keep your metabolism ticking over at the right speed.
As with all other nutrients, the most efficient way to supplement selenium is with food, unless your health professional has identified that you really do have a deficiency. The best food sources of selenium are Brazil nuts, vegetables in the brassica family, tuna, oysters, chicken livers, sesame seeds, sunflower seeds and whole grains. How much selenium is in your food will vary; so for best results, choose as wide a variety of foods as possible.