Selenium’s overlooked role in health, lifespan, and fertility

Selenium supports a variety of different selenoproteins and antioxidants that are important for our immune defense, circulatory system, cancer protection, metabolism, gut flora, fertility, nervous system, and general health. This is described in two meta-analyses that are published in Frontiers in Nutrition. The authors mention that there is widespread selenium deficiency in large parts of the world, Europe included, and that this is a public health problem. The big question is how much selenium we need to effectively prevent and treat many chronic illnesses.

Selenium is a trace element which plants absorb from the soil . The selenium content in soil varies from region to region, and that difference is reflected throughout the food chain. Although wholegrains, meat, offal, eggs, dairy products, and nuts are considered some of the best natural sources of selenium, their content of the mineral can vary by more than one thousand percent, depending on where the crops have been cultivated. The selenium content in plants is also lowered by factors like intensified farming methods. There is also selenium in fish and shellfish, but even with a balanced diet it can be a challenge to get enough.
It is possible to detect selenium deficiency by measuring the selenium content in serum or plasma. The selenium level should ideally be 85 micrograms per liter or higher. Toenail clippings can also be used to measure selenium levels. Even though selenium deficiency contributes to a lot of diseases and failure to respond properly to therapies, it is not common practice to measure selenium levels.
According to WHO, the selenium intake is too low in vast parts of the world, including Europe, large parts of China, Africa, India, and Brazil.
The authors behind a new meta-analysis and umbrella review analyzed more than 2,200 scientific articles, including 76 meta-analyses, to look closer at selenium’s role in relation to Keshan disease, virus infections, cancer, cardiovascular disease, thyroid disorders, intestinal diseases, impaired fertility, and neurological disorders.

Keshan disease and heart failure

The Keshan province is in the Northeastern part of China. Here, the soil is extremely low in selenium. Earlier, many people were affected by a life-threatening condition that is now known as Keshan diseases. It’s caused by a normally harmless RNA virus (Coxsackie B virus) that attacks the heart and may cause heart failure because the immune defense is weakened by the extreme selenium deficiency. In the 1960s, the Chinese people in that area systematically eradicated the disease with selenium supplements.

The immune defense and virus infections

Selenium is important for the immune defense that is designed to attack potentially dangerous microorganisms and pathogens swiftly and effectively. Selenium also helps the immune defense communicate, which is essential for its ability to regulate inflammatory processes. Selenium is also an antioxidant and prevents virus from mutating and becoming increasingly virulent. Premature development of HIV (human immunodeficiency virus), which is an RNA virus, is associated with low plasma levels of selenium. In general, malnutrition is a significant factor in the progression of AIDS. Lack of selenium also increases the risk of contracting other RNA viruses such as hepatitis B and COVID-19. Levels of selenium in the soil can indirectly determine whether infections like COVID-19 are harmless or tend to become life-threatening.

Cancer

Selenium has a variety of cancer-protective mechanisms, including gene regulation, repair of damaged DNA, the immune defense, regulation of inflammation, and apoptosis (programmed cell death). Selenium also supports several powerful antioxidant mechanisms that protect cells and their DNA against oxidative stress caused by free radicals.
Studies show that selenium taken in daily doses of 100-200 micrograms can lower the risk of different types of cancer and cancer-related deaths. Also, selenium supplements only appear to have a positive effect on people who lack selenium to begin with, which is the case in large parts of Europe and other places with low selenium content in the soil. Selenium yeast seems to have the best effect.

Cardiovascular disease

Cardiovascular disease is the leading cause of death worldwide. Ageing, smoking, an unhealthy lifestyle, hypertension, overweight, diabetes, and genetic factors increase the risk of cardiovascular disorders. Selenium, due to its antioxidant function, prevents cholesterol from oxidizing, which is the actual reason why this otherwise essential lipid is embedded in the blood vessel walls, where it sets the stage for atherosclerosis and cardiovascular disease.
Selenium also counteracts chronic inflammation. In the Swedish KiSel-10 study, 443 older people were randomly assigned to daily supplementation with either 200 micrograms of selenium yeast and 200 milligrams of pharmaceutical-grade Q10 or matching placebo for four years. The study showed that in the group that was supplemented with selenium and coenzyme Q10, the cardiovascular mortality was reduced by over 50 percent compared with the placebo group. Follow-up studies 12 years later also showed a significant and positive long-term effect on the circulatory system, heart health, and lifespan.

Thyroid disorders

The body needs selenium to convert the passive thyroid hormone T4 (with four iodine atoms) into the active T3 hormone (with three iodine atoms). Studies show that selenium supplementation has a positive effect as add-on therapy in the treatment of autoimmune thyroid disorders such as Hashimoto’s thyroiditis (that causes hypothyroidism) and Graves’ disease (that causes an overactive thyroid gland).
The thyroid gland contains relatively large amounts of selenium that is important for thyroid hormones and also serves as an antioxidant that protects the thyroid gland against oxidative stress and chronic inflammation.

Chronic intestinal disorders

Crohn’s disease and ulcerative colitis are common bowel disorders that are characterized by chronic inflammation. Over the past decades, the rate of these diseases has gone up due to unhealthy diets and environmental factors. Low selenium levels in the blood are linked to an increased risk of developing such bowel disorders and colon cancer. On the other hand, selenium supplementation can help prevent and control these disorders. This is because selenium supports the immune defense, helps control inflammation, regenerates the protective intestinal epithelium, and supports many other anti-cancer mechanisms. Selenium even has a positive influence on certain useful bacteria and the gut flora.

Impaired male and female fertility

Selenium supplementation can improve male fertility by increasing sperm cell motility. Because of its role as an antioxidant, selenium also protects sperm cells from free radical attacks that can otherwise cause DNA damage, and something called DNA fragmentation. Daily supplementation with 100-200 micrograms of selenium can increase sperm cell count and volume.
PCOS (polycystic ovary syndrome) is a common cause of infertility in women. It can cause irregular periods, hirsutism (excess hair growth around the mouth and chin), acne, fatigue, and sugar cravings. A study of 389 women showed a link between PCOS and lack of selenium.
Daily supplementation with 200 micrograms of selenium helps regulate levels of sex hormones and prevents PCOS-related imbalances. It is also important to have stable blood sugar levels when trying to improve fertility and the hormone balance. Selenium also has an important role in fetal development. Too little selenium can result in stunted growth of the fetus, low birth weight, and an increased risk of miscarriage.

Neurological diseases

The largest selenium concentrations in the brain are found in glands and the grey matter that consists of nerve cells and short dendrites. Selenium is important for nerve cell functions and for protection against oxidative stress. Lack of selenium can result in neurological disorders like Alzheimer’s disease, Parkinson’s disease, and epilepsy. Selenium appears to be able to reduce epileptic seizures in children and reduce the destruction of nerve cells in Alzheimer’s disease.

Selenium requirements and updated recommendations

According to the revised Nordic Nutrient Recommendations, men’s recommended daily selenium intake has increased from 60 to 90 micrograms, while women’s daily intake has gone up from 50 to 75 micrograms. Published studies suggest that we need 100-200 micrograms of selenium daily to optimize blood levels of the nutrient and reach an ideal level of around 125 micrograms per liter. According to the European Food Safety Authority (EFSA), 300 micrograms of selenium per day is the safe upper intake level.

References:

Puze Wang et al. Selenium intake and multiple health-related outcomes: an umbrella review of meta-analysis. Frontiers in Nutrition. 13 Sep. 2023

Yin Sun. Review on the health-promoting effect of adequate selenium status. Frontiers in Nutrition. 16 March 2023

Zhang J et al. Association between regional selenium status and reported outcome of COVID-19 cases in China. The American Journal of Clinical Nutrition. Apr. 2020

Pol Solé-Navais et al. Maternal Dietary Selenium Intake during Pregnancy Is Associated with Higher Birth Weight and Lower Risk of Small for Gestational Age Births in the Norwegian Mother, Father and Child Cohort study. Nutrients. December 2020

Malgorzata Dobrzynska el al. Natural Sources of Selenium as Functional Food Products for Chemoprevention. Foods 2023