Selenium is an important micronutrient. It is essential for life for both people and animals. The body cannot synthesize selenium and is dependent upon the selenium that it can get from food. In many regions of the world, there is too little selenium in the soil and in the food, and supplementation is necessary for optimal health.
Regions with selenium-poor soil
In many regions of the world, the content of selenium in the soil is quite low. In large parts of Asia, China in particular, and in much of Europe and the Middle East, there are low levels of selenium in the soil.
Plants accumulate inorganic selenium from the soil and convert it to organic selenium. In that way, the selenium enters the food chain. For example, cows eat grass containing selenium, and the some of the selenium enters the meat and the milk of the cows. People eat the meat and drink the milk. Too little selenium in the soil means too little selenium in the food.
The Finnish experiment with selenium additives to fertilizer
In 1985, the Finnish government decided that selenium should be added to all agricultural fertilizer. The background to this decision was an intense debate in which advocates of selenium additives presented data about the low levels of selenium in Finnish citizens. The selenium status of Finnish citizens had reached such a low level that public health authorities in Finland were worried about the dangers of selenium deficiency.
The success of the selenium fertilizer project in Finland
Twenty years later in 2005, the Finnish authorities issued a report summing up the first 20 years of the selenium fertilizer project. The new data showed that adding selenium to agricultural fertilizer has been a safe and effective solution to the problem of low selenium status in the Finnish people. Actually, the measurements of the selenium in blood samples, in milk samples, and in meat samples all showed a positive trend, except in organic farming areas where the use of artificial fertilizers was not permitted.
Not enough selenium to copy the Finnish experiment
Despite the success of the Finnish experiment, none of the other countries in the rest of Europe has taken a similar decision. One important reason is that selenium is a rare trace element, and there is relatively little selenium produced every year. Of the amount that is produced, the preponderance goes to industrial purposes.
There is, simply put, not enough selenium available to fertilize cultivated fields and pasture lands with it everywhere in the selenium-poor countries of the world to the extent that the Finns have done. Selenium is so relatively rare that we humans need to administer its uses carefully and should begin to stockpile it for the use of future generations [Haug].
Recommended dietary intake for selenium
Today, in the United States and Canada and many countries in Europe, the recommended dietary intake for selenium is set at 55 micrograms per day. This is the daily intake level at which it is thought that the activity of the selenium-dependent antioxidant enzyme glutathione peroxidase can be optimized.
Since the establishment of this intake level, selenium researchers have suggested that greater intakes may be needed for selenium-dependent protection against cancer and other chronic diseases. The putative beneficial range is plasma selenium status between 120 and 170 nanograms per milliliter [Hurst 2010]. The evidence from Hurst’s research seems to indicate that we need approximately 105 micrograms per day to reach the lower limit of that range and approximately 155 micrograms per day to reach the upper limit of that range. Both intakes are well under the tolerable upper limit for daily intakes established by the European Food Safety Authority in February, 2006: 300 micrograms of selenium per day.
Special groups at risk of getting too little selenium
Even at the recommended level of 55 micrograms of selenium per day, there can be special groups of people at risk of getting too little selenium in their diets. For example, vegetarians and vegans are likely to be at risk because meat, fish, and dairy products are important sources of dietary selenium.
Another group that may be at risk is the group of people who are sensitive to gluten and who therefore avoid grain products. Grains are just below fish and meat from mammals on the list of important dietary sources of selenium.
Elderly people who eat less may be at risk. Smokers may need extra selenium. Body size and exercise levels may influence the amount of selenium needed on a daily basis.
Selenium and selenocysteine and selenoproteins
Selenoproteins are proteins in the body that contain selenocysteine, the 21st amino acid. Selenocysteine is itself dependent upon the availability of selenium for its synthesis. Researchers have identified 25 selenoproteins that play a role in human health. These selenoproteins have several biological functions:
- act as antioxidants that protect the cells and the DNA against oxidative damage
- activate thyroid hormones
- strengthen the immune system
- protect the prostate gland
- aid the production of healthy sperm cells
- contribute to the development of the brain
Selenium and selenoprotein P
One of the most important selenoproteins is the selenoprotein P. It is the most abundant selenoprotein in the blood plasma, making up 25 – 50 percent of the total selenium in plasma. It is an important selenoprotein for the protection of the prostate gland. It is a useful bio-marker for selenium status in humans because it is more sensitive to low and medium levels of plasma selenium than glutathione peroxidase is [Hurst 2010].
Danish study of men’s selenium status
In a cross-sectional study of 27,000 men done in Denmark, the data showed that 80 % of the men had too little selenium in the blood to optimize the activity of selenoprotein P. The study, which was published in the British Journal of Nutrition in 2016, had as its objective to see whether low selenium status amounted to a health risk for Danish men. In the study, higher levels of plasma selenium and selenoprotein P were associated with lower risks of high-grade cancer [Outzen].
Low selenium status and risk of prostate cancer
The results from the Danish study correspond to the results from a comparable study undertaken in the Netherlands. In the Dutch study, the data showed that higher toenail selenium levels were associated with substantial decreases in the risk of advanced prostate cancer. Toenail selenium levels are regarded as a better long-term marker of selenium status than plasma or serum selenium levels are [Geybels].
Summary: What is selenium?
Selenium is a rare and essential micronutrient not synthesized in the body
Selenium is a rare micronutrient that we humans cannot produce for ourselves and that is essential for good health. In that we cannot synthesize it ourselves and that we need it, selenium is similar to the vitamins. It is also like vitamin C and vitamin E in the sense that it serves as an important antioxidant through its incorporation in selenoproteins.
Selenium is used mostly for industrial purposes
Selenium is a by-product of the mining of copper. By far, the greatest use of the earth’s selenium resources is industrial in the production of electronic, metal, and glass products. For example, selenium is used to make red glass products. Only about 10 % of the world’s annual production of selenium is used to fertilize agricultural land. Much less than 10 % is available for use in nutritional supplements.
Selenium is unevenly distributed in the world
The uneven distribution of selenium in the world is a worrisome problem. Nearly 70 % of the selenium reserves on Earth is concentrated in four countries: Chile (25 %), Russia (20 %), Peru (13 %), and the USA (10 %), There are no known large reserves anywhere in Europe. The reserves of selenium are so relatively small that some researchers are suggesting that the present use of selenium be administered carefully and that selenium be stockpiled for the use of future generations.
Adequate intakes of selenium are necessary for good health
Research has shown that adequate intakes of selenium are necessary for good cell metabolism, strong immune response, production of healthy sperm cells, protection of cell and DNA structure and function, and for healthy hair and nails. Some epidemiological studies suggest that adequate selenium status is associated with the prevention of chronic diseases.
Geybels, M. S., Verhage, B. J., van Schooten, F. J., Goldbohm, R. A., & van den Brandt, P. A. (2013). Advanced prostate cancer risk in relation to toenail selenium levels. Journal Of The National Cancer Institute, 105(18), 1394-1401.
Haug, A., Graham, R. D., Christophersen, O. A., & Lyons, G. H. (2007). How to use the world’s scarce selenium resources efficiently to increase the selenium concentration in food. Microbial Ecology In Health And Disease, 19(4), 209-228.
Hurst, R., Hooper, L., Norat, T., Lau, R., Aune, D., Greenwood, D. C., & Fairweather-Tait, S. J. (2012). Selenium and prostate cancer: systematic review and meta-analysis. The American Journal Of Clinical Nutrition, 96(1), 111-122.
Hurst, R., Armah, C. N., Dainty, J. R., Hart, D. J., Teucher, B., Goldson, A. J., & Fairweather-Tait, S. J. (2010). Establishing optimal selenium status: results of a randomized, double-blind, placebo-controlled trial. The American Journal Of Clinical Nutrition, 91(4), 923-931.
Outzen, M., Tjønneland, A., Larsen, E. H., Friis, S., Larsen, S. B., Christensen, J., & Olsen, A. (2016). Selenium status and risk of prostate cancer in a Danish population. The British Journal Of Nutrition, 115(9), 1669-1677.