Iodine is an essential component of the thyroid hormones. After iodine, selenium is arguably the micronutrient most important to the thyroid gland. Proportionally, there is more selenium in the thyroid gland than there is selenium in any other organ in the body. There are good reasons for the presence of selenium in the thyroid gland. Iodine and selenium are both required for thyroid hormone synthesis and function.
Our bodies do not make selenium. We must get the selenium that we need from our food and from supplements. The selenium that we absorb is incorporated into the amino acid selenocysteine. Selenocysteine, then, is a necessary component of some 25 selenoproteins that are needed for various biological functions.
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].
There have been some recent research results relating to selenium supplementation and prostate gland tissue. Researchers in The Netherlands have published results showing that a five-week daily intervention with a high-selenium yeast supplement, 300 micrograms daily, is associated with a down-regulation of genes that are involved with cellular growth and proliferation, with cellular immune response, and with inflammation processes. Also down-regulated by the selenium supplementation is the activity of genes involved with wound-healing [Kok 2017].
The Dutch study was a randomized, double-blinded, placebo-controlled study. Interestingly, the researchers saw the opposite effect in the placebo group. In the placebo group, there was an up-regulation of the genes involved in cellular immune response [Kok 2017].
Selenium supplementation and the risk of prostate cancer? What do we know? We need to be careful in interpreting the research results that we have (and we need more research), but, yes, there is evidence for an inverse association between prostate cancer risk and selenium status [Hurst 2012].
As of this writing (April 2017), the protective effect of selenium supplementation against prostate cancer seems to be found in a relatively narrow range of plasma selenium status [Hurst 2012]. Furthermore, there seems to be a U-shaped relationship between selenium status and protection against prostate cancer.
If the concentrations of selenium in the plasma are too low, there is increased risk of prostate cancer. This is a serious concern in many regions of the world.
Authors of a recent meta-analysis of 69 studies of selenium exposure and cancer risk have concluded that high selenium exposure can reduce cancer risk, especially high selenium exposure that is reflected in high plasma or serum selenium status and/or in high toenail concentrations [Cai 2016]. Admittedly, higher selenium intakes (as compared to lower selenium intakes) can affect different forms of cancer differently. We still need more research to sort out which forms and dosages of dietary and supplemental selenium are most effective at reducing cancer risk. In this article, I want to summarize the findings of Dr. Xianlei Cai and colleagues.
What is a meta-analysis of selenium exposure and cancer risk?
A meta-analysis is a research method of combining the data from several selected research studies to reach conclusions that have greater statistical power. In the present case, Cai et al selected 69 studies that met their inclusion criteria. Each one of the 69 selected studies had the following characteristics:
There have been two noteworthy discoveries from a recent randomized controlled trial conducted by Dr. Urban Alehagen of Linköping University (Sweden) and his colleagues.
Firstly, people with low concentrations of selenium in their blood were found to be at significantly higher risk of death from heart disease.
Secondly, a combination of a patented high selenium yeast supplement and a proven Coenzyme Q10 supplement taken daily for four years provided significant protection against heart disease in people with low serum selenium status.
The KiSel-10 study of cardiovascular mortality
The study enrolled 668 healthy elderly individuals aged 70-80 years. The study was well-designed and well-executed. One group of 219 randomly selected individuals received 200 micrograms of selenized yeast tablets and 200 milligrams of Coenzyme Q10 capsules daily for four years. A second randomly assigned group of 222 individuals received matching placebos. The remaining group of 227 individuals received no treatment at all.
The heart muscle tissue is frequently the first tissue in humans to suffer damage caused by selenium deficiency. When the cell membranes in the heart muscle tissue are damaged by the action of harmful free radicals (this is called oxidative damage), many of the healthy heart muscle cells are replaced by fibrous tissue. The resulting condition is called cardiomyopathy.
Cardiomyopathy is a disease of the heart muscle in which the heart is enlarged, thick, and rigid [Mayo Clinic]. As the cardiomyopathy worsens, the weakened heart muscle is less and less able to pump adequate quantities of blood to carry oxygen and nutrients to the cells and tissues throughout the body. Eventually, symptoms such as shortness of breath, early fatigue, and swelling in the legs and feet and abdomen appear, the symptoms of chronic heart failure.
Statin medications: good news and bad news? On the one hand, statin medications are effective at reducing cholesterol levels, and, are good, apparently, at reducing the number of deaths from heart attacks. On the other hand, we have seen a very considerable rise in the number of cases of chronic heart failure … in the same period that statin medications have been prescribed. Drs. Okuyama and Langsjoen and their colleagues have explained the pharmacological mechanisms by which this medical paradox may be occurring [Okuyama].
Statins inhibit the body’s production of Coenzyme Q10
Okay, I was aware of the evidence from well-designed studies linking the taking of statin medications to decreased plasma levels of Coenzyme Q10. Coenzyme Q10 is an important factor in cellular energy production and is an important lipid-soluble antioxidant [Folkers, Littarru, McMurray]. And I knew that the energy-deprived heart is a failing heart [Folkers, Molyneux, Mortensen]. So, I knew that anyone taking a statin medication needs to talk to his or her cardiologist about taking a good Coenzyme Q10 supplement.
How much selenium from food and supplements do we need on a daily basis? Which bio-markers of optimal selenium status seem to be most useful to answer this question? Dr. Rachel Hurst and Dr. Susan J. Fairweather-Tait, Norwich Medical School, United Kingdom, and their colleagues set out to find answers. The design of their study is very interesting.
They enrolled 119 healthy British men and women aged 50 – 64 years in a randomized, double-blind, placebo-controlled study that lasted 12 weeks [Hurst]. They excluded the following persons from the study:
people with already high plasma selenium status
people with long-term illnesses
people on various medications
people unwilling to discontinue taking vitamins and herbal remedies at least one month prior to the start of the study
selenium-enriched yeast tablets containing 50, 100, or 200 micrograms of a patented organic selenium (SelenoPrecise® preparation delivered by Pharma Nord, Denmark)
selenium-enriched onion meals that provided the equivalent of 50 micrograms of selenium per day
unenriched onion meals that provided the equivalent of less than 4 micrograms of selenium per day
Measurements of selenium
Remember: Selenium is a trace element. We measure its intake in micrograms per day, not milligrams. We measure selenium status in plasma and serum in terms of micrograms per liter (or equivalently, in nanograms per milliliter). Selenium in toenails or hair, then, we measure in micrograms per gram.
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.