The proper daily dosage of selenium for normal people? Normal people? How many of us are approximately normal? 68 percent of us, perhaps? Yes, we humans are more the same in many ways than we are different. However, there is considerable biochemical variation amongst us humans. So, it is difficult to say who is average and normal and then suggest an ideal daily dosage of selenium.
What do the numbers from selenium studies say?
Let’s look at the numbers from published research and see what sense we can make of them. Remember: we humans need adequate plasma selenium concentrations for optimal antioxidant and anti-viral and anti-carcinogenic protection [Schrauzer 2009].
Putative beneficial range for plasma selenium status
Hurst and Fairweather-Tait et al, researchers based at Norwich Medical School, University of East Anglia, in the United Kingdom have suggested that the “putative beneficial range” lies between 120 and 150 nanograms of selenium per milliliter of plasma [Hurst 2010].
This gives us a starting point. How do we keep our plasma selenium status at that level?
In 2010, Hurst and Fairweather-Tait and their colleagues reported the results of a randomized controlled trial of supplementation with a high selenium yeast preparation in healthy British men and women aged 50 – 64 years. The average baseline plasma selenium concentration in the study participants was 95.7 nanograms per milliliter, clearly below the suggested beneficial range.
Ten weeks of supplementation with a daily 50-microgram high-selenium yeast tablet raised the participants’ plasma selenium concentrations to an average of 118.3 nanograms per milliliter.
Ten weeks of supplementation with a daily 100-microgram high-selenium yeast tablet raised the participants’ plasma selenium concentrations to an average of 152.0 nanograms per milliliter.
The daily 50-milligram high selenium yeast tablet brought the participants up to the lower limit of the putative beneficial range. The daily 100-microgram high selenium yeast tablet brought the participants up to the upper limit of the putative beneficial range.
But, remember, these results reported by Hurst, Fairweather-Tait, et al were obtained in men and women of Caucasian background aged 50 – 64 years who had a clearly low baseline plasma selenium concentration. We should be careful about generalizing from this quite homogeneous sample to much more diverse populations.
Plasma selenium levels and risk of prostate cancer
In 2012, Hurst and Fairweather-Tait and their colleagues published the results of a systematic review and meta-analysis of research results from randomized controlled trials, case-control studies, and prospective cohort studies. Altogether, they looked at 12 studies with a total of 13,254 study participants.
Their meta-analysis showed that plasma selenium concentrations in the range from 120 nanograms per milliliter up to 170 nanograms per milliliter were associated with decreased risk of prostate cancer [Hurst 2012]. This is useful information.
Plasma selenoprotein levels
Selenium carries out its biological functions primarily as a component of the amino acid, selenocysteine. Selenocysteine is, in turn, a component of 25 selenoproteins. Among the better known selenoproteins are the glutathione peroxidases, the thioredoxin reductases, the iodothyronine deiodinases, and selenoprotein P.
By this time, you may be wondering why are we looking so much at plasma selenium levels? Wouldn’t it be better to look at plasma levels of some of the important selenoproteins? What do the studies show?
Plasma and platelet levels of glutathione peroxidase
Hurst, Fairweather-Tait, et al give us some numbers that we can look at. For example, in their randomized controlled trial of high selenium yeast supplementation of healthy British men and women aged 50 – 64 years, they found that dosages of 50, 100, and 200 micrograms per day did not significantly change plasma glutathione peroxidase levels or platelet glutathione peroxidase levels.
Even in study participants with a somewhat low average baseline status (95.7 nanograms per milliliter), plasma glutathione peroxidase and the platelet peroxidase were not sensitive enough markers of selenium status.
Background note: Glutathione peroxidase is the name of a whole family of antioxidant enzymes that protect the cells and tissues against oxidative damage caused by harmful free radicals. Glutathione peroxidase usually accounts 10% to 30% of the total selenium in the plasma.
Remember: selenium does not float around in the body in the form of the single element; it is found nearly everywhere as a component of a selenoprotein.
Optimal glutathione peroxidase activity seems to reach a plateau at plasma concentrations in the range from 70 – 90 nanograms per milliliter. Consequently, plasma glutathione peroxidase seems to reach its optimal activity at levels below the levels that are thought to correlate with reductions in cancer risk [Hurst 2010]. Neither plasma nor platelet glutathione peroxidase status is not sensitive enough to be a marker for adequate selenium intake and status.
Plasma levels of Selenoprotein P
Selenoprotein P is the most abundant selenoprotein in plasma, accounting for approximately 25% – 50% of the total selenium in the plasma. It is especially rich in selenocysteine, the 21st amino acid that is a vital component of the selenoproteins. Selenoprotein P functions as an antioxidant; it has other biological functions as well.
Plasma selenoprotein P concentration is arguably a better index of selenium status sufficiency than glutathione peroxidase because the glutathione peroxidase activity reaches optimal levels at lower plasma concentrations.
Plasma selenoprotein P concentrations
The Hurst study – remember the characteristics of the study sample – showed plasma selenoprotein P concentrations beginning to plateau at 110 – 118 nanograms per milliliter.
Compare with plasma glutathione peroxidase activity seeming to plateau at 90 nanograms per milliliter [Duffield 1999].
Caution: Many factors affecting selenium status
Remember, it is difficult to specify which amounts of daily selenium intake will result in which beneficial plasma (or serum) selenium levels for all individuals. There are just too many factors that influence the uptake of the selenium in our food and in our selenium supplements.
Dietary factors inhibiting selenium uptake
Some minerals and other dietary components may inhibit the uptake of selenium. Schrauzer identified a lengthy list of minerals and heavy metals in food and water that selenium will interact with, many of them antagonistic to selenium. When selenium binds together with heavy metals, e.g. mercury or cadmium, the effect is a beneficial detoxification. However, the binding together of selenium with other elements will result in a lowered reservoir of selenium for physiological purposes [Schrauzer].
Biochemical differences affecting selenium uptake
The ability to absorb selenium from the digestive system varies from individual to individual. For example, there is some evidence that the response to selenium intakes may vary according to sex [Ogawa-Wong]. Age may well play a role in the response to selenium intakes [Thompson].
Many selenium studies have been done in mostly Caucasian samples drawn in the United States and Europe. We need to know about the response to selenium supplementation in other populations.
Selenium supplement formulations and uptake
Different formulations of the selenium supplement may well affect the speed and extent to which supplementation changes plasma selenium status. At present, the best formulation for reducing the risk of cancer is the organic high-selenium yeast formulation.
The high-selenium yeast selenium supplement seems to be better absorbed and better retained in the body than the synthetic L-selenomethionine formulation and the inorganic sodium selenite formulation [Bügel; Larsen].
What can we do with these numbers?
For those of who don’t know how much selenium we are getting in our food, perhaps a good place to start is to get a plasma or serum Se test? Once we have an idea of our plasma selenium status, we can consider how much daily supplementation we think we need: 50 or 100 micrograms per day?
The combination of high-selenium yeast tablets and Coenzyme Q10 capsules
One last thought: worth mentioning too is the existence of a special inter-relationship between the micronutrient selenium and the bio-nutrient Coenzyme Q10. Taken in combination, the two supplements seem to give a better health outcome [Alehagen].
Sources
Alehagen, U., & Aaseth, J. (2015). Selenium and coenzyme Q10 interrelationship in cardiovascular diseases–A clinician’s point of view. Journal of Trace Elements in Medicine and Biology, 31157-162.
Alfthan G., Aro A., Arvilommi H., Huttunen J.K. (1991). Selenium metabolism and platelet glutathione peroxidase activity in healthy Finnish men: Effects of selenium yeast, selenite, and selenate. Am. J. Clin. Nutr. 53:120–125.
Bügel, S., Larsen, E. H., Sloth, J. J., Flytlie, K., Overvad, K., Steenberg, L. C., & Moesgaard, S. (2008). Absorption, excretion, and retention of selenium from a high selenium yeast in men with a high intake of selenium. Food & Nutrition Research, 52doi:10.3402/fnr.v52i0.1642.
Duffield A.J., Thomson C.D., Hill K.E., Williams S. (1999). An estimation of selenium requirements for New Zealanders. Am. J. Clin. Nutr. 70:896–903.
Duffield, A. J., Thomson, C. D., Hill, K. E., & Williams, S. (1999). An estimation of selenium requirements for New Zealanders. The American Journal Of Clinical Nutrition, 70(5), 896-903.
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.
Larsen, E. H., Hansen, M., Paulin, H., Moesgaard, S., Reid, M., & Rayman, M. (2004). Speciation and bioavailability of selenium in yeast-based intervention agents used in cancer chemoprevention studies. Journal Of AOAC International, 87(1), 225-232.
Ogawa-Wong, A. N., Berry, M. J., & Seale, L. A. (2016). Selenium and Metabolic Disorders: An Emphasis on Type 2 Diabetes Risk. Nutrients, 8(2), 80.
Schrauzer, G. N. (2009). Selenium and selenium-antagonistic elements in nutritional cancer prevention. Critical Reviews in Biotechnology, 29(1), 10-17.
Thompson, P. A., Ashbeck, E. L., Roe, D. J., Fales, L., Buckmeier, J., Wang, F., & Lance, P. (2016). Selenium Supplementation for Prevention of Colorectal Adenomas and Risk of Associated Type 2 Diabetes. Journal of The National Cancer Institute, 108(12),
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