WARNING!
This is an older article that may not reflect Dr. Mercola’s current view on this topic. Use our search engine to find Dr. Mercola’s latest position on any health topic.
Selenium is an essential element your body requires in small amounts.1 Like all essential elements you get it from your food, but be aware that it can be toxic at high levels if you’re taking supplements.
Selenium functions as part of the amino acid selenocysteine, found in selenocysteine-containing proteins, also called selenoproteins. Those who are deficient may find physiological responses to stress are affected. For example, in parts of Asia, selenium deficiency has been associated with a certain form of cardiomyopathy and a form of osteoarthropathy.
Levels of selenium found in plant food will vary depending upon the amount in the soil where the plants are grown. The risk of selenium deficiency can increase following bariatric surgery; those who have severe gastrointestinal conditions, such as Crohn's disease, are also at increased risk.
Others with metabolic disorders such as homocystinuria and maple syrup urine disease may need supplementation to ensure optimal levels. The dietary reference intake for selenium was revised in 2000, which currently lists 55 micrograms per day (μg/day) for adults 19 years and older. Requirements rise with pregnancy and breastfeeding to 60 μg/day and 70 μg/day respectively.
Low Selenium Level Associated With Poor Bone Mineral Density
Researchers are increasingly recognizing selenium deficiency as a health risk for a number of conditions.2 As such, the authors of several studies have investigated associations with bone mineral density, thyroid function and selenium levels.
A recently published study3 appeared in BMC Musculoskeletal Disorders in which the researchers examined the correlation between dietary selenium and osteoporosis in a middle-aged and older population in China. Data were collected using a “validated semi-quantitative food frequency questionnaire,” and osteoporosis was diagnosed using bone mineral density scans.
The study began with 6,267 subjects, in which the prevalence of osteoporosis was 9.6%. Higher rates of osteoporosis were associated with lower levels of selenium; the results were consistent in men and women.
In a second study4 investigators sought to determine whether selenium affects thyroid function and bone mineral density. They included 387 elderly men and found that selenium levels were positively associated with bone mineral density. This appeared independent of thyroid function, which was not affected by selenium.
A group of European scientists5 sought to identify variations in selenium in postmenopausal women with healthy thyroid status. The researchers were looking for differences in bone turnover, bone mineral density and the susceptibility women had for fracture.
The study, published in 2012, was designed to include participants from five European cities. Those with thyroid or bone metabolism issues were excluded, leaving a study population of 1,144. Blood levels of selenium and selenoprotein P, as well as serum levels of T3, T4 and TSH were measured.
Bone turnover markers, bone mineral density and vertebral, hip and nonvertebral fractures were also recorded. Once the data were analyzed, the researchers concluded selenium levels were “inversely related to bone turnover and positively correlated with [bone mineral density],” independent of thyroid status.
Selenium Plays an Important Role in Heart Health
Heart disease is the leading cause of death for many groups in the U.S. The CDC reports nearly 25% of all deaths are the result of heart disease. A number of nutrients play a role in your heart health, including the combination of selenium and CoQ10, which have been found to reduce your risk of mortality.
Low intake of selenium and reduced production of CoQ10 that occurs with age raise your risk of heart disease. Participants in one study demonstrated a reduced risk of cardiovascular mortality with CoQ10 and selenium dietary supplements.
Twelve years after the study was completed, the original participants were evaluated again and it was found they continued to demonstrate a reduction in cardiovascular mortality.
Researchers also found those who used selenium and CoQ10 supplements showed significant reduction in ischemic heart disease, high blood pressure, impaired functional heart capacity and diabetes. It appeared the protective action was not confined to just the interventional period, but persisted during the follow-up as well.
At the cellular level, selenium is an active element of glutathione peroxidase, an enzyme responsible for converting hydrogen peroxide to water, and serving as the first line of defense against harmful free radicals.
Optimal Levels of Selenium May Cut Risk of Serious Disease
Unless you’re taking a supplement, it's not likely you will consume too much selenium from your food. As with other micronutrients, too much is not better. In one cross-sectional study6 of 5,423 participants, researchers found a higher prevalence of diabetes in those who consistently consumed higher amounts of selenium, such as might be found in a daily supplement.
Conversely, suboptimal levels of selenium have a negative affect on several bodily systems, in part associated with the role selenium plays in protecting against free radical damage.7 Some of the health conditions affected by suboptimal levels of this essential element include:
• Thyroid function — Tissue with the highest density of selenium is your thyroid gland, required for the function and metabolism of thyroid hormones. Maintaining optimal levels of selenium helps prevent thyroid disease. Supplementation may also be helpful for those with a condition known as Graves orbitopathy.8
• Immune system — The immune system relies on dietary selenium and the biological effects of selenoproteins. When selenium processes are dysregulated, a number of problems can arise including inflammation and diseases that are mediated by the immune system.9
• Asthma — In studies evaluating supplementation with selenium, researchers have found a rise in quality of life scores10 and improvement in clinical symptoms,11 but without association to secondary outcomes or those that could be validated with lung function tests.
• Fertility — Supplementation in men with low levels of selenium increased sperm motility in 56% of the intervention group.12 Selenium and selenoproteins are found in high levels in a healthy ovarian follicle, which may play a vital role in the development of a healthy egg, improving a woman's fertility. One researcher from a study evaluating selenium and female reproduction commented:13
"Infertility is a significant problem in our society. Further research is needed to better understand how selenium levels could be optimized, helping to improve women's chances of conceiving. Too much selenium can also be toxic, so it isn't just a case of taking multiple supplements."
Recommended: Three Brazil Nuts Daily
According to the International Osteoporosis Foundation, osteoporosis affects approximately 10% of women age 60, rising to 40% of women by age 80. The condition increases the risk of bone fractures, including hip fractures notorious for raising a senior’s risk of death.
The best approach to maintaining healthy bones and preventing osteoporosis is to get sufficient nutrients your body uses to build and maintain strong bones. In addition to maintaining optimal levels of selenium, consider other strategies discussed in my past article, “How To Help Prevent Osteoporosis.”
Although it's easy to get enough selenium from nutritional sources, supplements have become more popular as the powerful benefits of selenium antioxidant activity become more well known. Seek first to get selenium from your diet to avoid toxicity from too much supplementation, or from inorganic sources that are not as bioavailable.
The best food source is Brazil nuts, which average 70 to 90 mcg of selenium per nut depending upon the selenium content in the soil.14 Just two to three of these help meet your daily requirement. In combination with other food sources such as sardines, pastured organic eggs, wild-caught salmon and sunflower seeds, you can get all the selenium you need from food alone.