Selenium: what does it do, how much do we need, what are the symptoms of too much and too little and what are the best food sources of seelnium?
Nowadays, much is known about vitamins and minerals. But by no means everything. Sometimes it amazes me how much we still have to discover.
One of the less well studied minerals is selenium. Health authorities around the world make very cautious statements about the effect of selenium on the human body. Scientists do see a connection between intake of selenium and the development of certain diseases or disorders but are still very careful to make firm statements about this. In this article I summarize what is known about selenium so far and what we should do with this information.
The mineral selenium is a trace element, which means that the human body only needs a small amount of it. Most of the selenium in the body is stored in muscle tissue; the thyroid contains the highest concentration.
What does selenium do?
Selenium is an essential component of several enzymes and proteins called selenoproteins. Selenoproteins help make DNA and protect against cell damage and infections, among other things. These proteins are also involved in the reproduction and metabolism of thyroid hormones.
Selenium is also an antioxidant. It is part of the enzyme glutathione peroxidase. Glutathione peroxidase often interacts with vitamin E, another antioxidant. Glutathione peroxidase prevents the formation of free radicals. Do you want to know more about antioxidants and free radicals? Please read this article.
Selenium and iodine have a synergistic relationship (synergistic means they reinforce each other) that is especially important for a healthy thyroid gland. Iodine is a component of the thyroid hormone and selenium as a selenoprotein helps the thyroid hormone do its job. Both minerals in adequate amounts are necessary for the thyroid gland; too much or too little of either can contribute to thyroid problems.
Selenium deficiency can cause damage to the heart. The heart disease associated with selenium deficiency is called Keshan disease after one of the provinces in China where it was studied. It is characterized by heart enlargement. The soil in China is very poor in selenium. Eating plants rooted in Chinese soil therefore does not help get enough selenium. That is why a large part of scientific research into selenium and health takes place in China. Unfortunately, only a small part of the research has been translated into English.
How much selenium do we need?
In the Netherlands, the recommended dietary allowance of selenium for adults is 70 micrograms per day.
For a safe intake of selenium, the European Food Safety Authority (EFSA) has set the acceptable upper limit of 300 micrograms (for adults) per day. The tolerable upper limit is the maximum daily intake that is unlikely to have harmful effects on health.
Selenium deficiency
Two conditions are associated with severe selenium deficiency: 1) Keshan disease, a disease of the heart muscle, and 2) Kashin-Beck disease, a form of osteoarthritis (a condition in which the cartilage in a joint wears away).
Symptoms of selenium deficiency include nausea and vomiting, headache, mental confusion and seizures.
Toxicity
Chronically high intakes of selenium can lead to health problems ranging from having a metallic taste and bad breath, muscle tremors, hair loss, upset stomach and dizziness, to more serious consequences including heart attacks, respiratory distress or kidney failure.
Brazil nuts are exceptionally high in selenium, even when grown in soil with a low selenium content. Just one nut contains more than the recommended dietary allowance (RDA). Eating too many of these nuts on a daily basis can lead to toxic levels, as can using supplements containing selenium above the RDA.
The best sources of selenium
The amount of selenium in foods can vary greatly depending on the selenium content of the soil in which it is grown. Plants extract selenium from the soil, which then affects the amount of selenium in animals that eat those plants. Selenium-rich food sources include Brazil nuts, seafood and grains.
One Brazil nut a day is enough to maintain your selenium intake (well, the size of Brazil nuts varies quite a bit, here I mean a big nut). By the way, Brazil nuts are also an excellent source of copper, which we talked about just recently.
I have made a top-5 for you of the best plant sources of selenium. The data comes from Food Data Central. The amount of selenium is indicated per 100 g:
- Brazil nuts: 1920 micrograms;
- Flaxseed: 136 micrograms;
- Sunflower Seeds: 80 micrograms;
- Oatmeal: 29 micrograms;
- Brown Rice: 25 micrograms.