Selenium’s role as an antioxidant in a number of different diseases
Over the past decades, numerous studies have linked low selenium levels in the blood to cardiovascular disease, cancer, increased risk of infection, thyroid disorders, and several other diseases. Due to the widespread problems with selenium deficiency, supplementation with this nutrient is of potential value to our general health. In a review article that is published in Oxidative Medicine and Cellular Longevity, the authors look at selenium’s role in connection with a host of different diseases and metabolic disorders.
Selenium used to be viewed as a toxic compound but science has realized that it is in fact an essential trace element that we humans need in sufficient quantities. The reason is that selenium supports well over 25 identified selenoproteins that are important for the energy turnover, thyroid function, immune defense, fertility, neuron formation, and a number of other functions.
Several selenoproteins also serve as powerful antioxidants that protect cells against free radical damage. We humans produce free radicals as a natural byproduct of metabolic processes. The free radical load is increased by things like ageing, poisoning, smoking, etc. It’s important for antioxidants to keep the free radicals in check and prevent what is known as oxidative stress, a condition where free radicals wreak havoc. It is particularly dangerous when free radicals attack and oxidize cholesterol and polyunsaturated fatty acids in the cell membranes. This causes lipid peroxidation where free radicals start chain reactions in cells and tissues. Oxidative stress sets the stage for atherosclerosis, cellular DNA damage, and damage to other parts of the cells and this may result in a myriad of different diseases.
In their review article, the scientists looked closer at selenium’s role in health with specific focus on different selenium-containing antioxidants such as GPX 1-6 (glutathione peroxidases), selenoprotein P, and TXNRD 1-3.
Selenium in the different organs, and the body’s selenium status
Our organs contain different quantities of selenium. We have around 30 percent of our selenium in our liver and muscle tissue, while there is 15 percent in the kidneys and other organs, and 10 percent in our plasma. In the case of a selenium deficiency, however, this distribution is thrown off balance because the body is forced to prioritize the most important selenium-dependent functions. The brain, thyroid gland, testicles, and muscles are therefore able to retain or reabsorb selenium, while drastic drop in selenium concentrations may occur in the liver, lungs, muscles, skin, and other tissues. The cells also seem to give first priority to selenium for handling energy turnover and reproduction, whereas the protective antioxidant effect of the nutrient is down-prioritized.
The body’s current selenium’s status is usually determined by means of a blood test. It is possible to assess the body’s selenium status over a longer period of time by measuring the selenium content in hair or nails.
- Data from Europe and several places in China, Asia, the Middle East, and Africa show that people are not getting enough dietary selenium
- This is mainly because of selenium-depleted soils, and this problem is reflected throughout the entire food chain.
Selenium, cancer, metabolic disorders, and inflammation
The authors also mention population studies that link high selenium levels in the blood to lower mortality. Conversely, low selenium levels in the blood are related to increased mortality, including mortality from cancer.
Moreover, it has been found that low selenium status is associated with cardiac failure, thyroid disorders, anemia, iron deficiency, and elevated levels of CRP (C-reactive protein), which is an inflammation marker.
Science has recently discovered that low selenium status is even linked to metabolic syndrome (an early stage of type 2 diabetes) that involves problems like elevated blood sugar levels, elevated cholesterol levels, and a high BMI. Metabolic syndrome is currently spreading like a bushfire.
The scientists therefore call for increased focus on the correlation between selenium deficiency and cancer, inflammation, and metabolic disorders.
Selenium and cardiovascular disease
Coronary occlusion is the leading cause of death in the western world. Selenium’s ability to protect against cardiovascular disease is primarily because of selenium-containing antioxidants such as GPX (glutathione peroxidase) that counteracts the lipid peroxidation of cholesterol, which is a major cause of atherosclerosis. The selenium-containing antioxidants also protect against chronic inflammation, another contributing factor.
In their article, the authors mention a meta-analysis that documents that patients with cardiovascular disease have lower selenium levels in their blood than healthy people do. Other studies have revealed that having sufficient amounts of selenium in the blood can protect against cardiovascular disease.
They also refer to the Swedish KiSel-10 study where 443 healthy seniors were randomly assigned to a daily supplement of 200 micrograms of selenium and 200 mg of coenzyme Q10, or matching placebo. The study lasted five years and showed that the people who got the active supplements had a 54% lower cardiovascular mortality rate compared with the group that got placebo. A follow-up of the study showed that the two supplements had a positive impact on life expectancy and quality of life.
The reason for combining selenium and coenzyme Q10 is that the farmland in Sweden contains very little selenium, and our endogenous Q10 synthesis decreases as we grow older. Q10 is important for our energy turnover but also has a vital role as an antioxidant, and various selenoproteins are needed for optimal utilization of Q10 in the energy production, so it makes perfect sense to give both nutrients to older people. The KiSel-10 study is remarkable by several accounts, especially because it focuses on how seniors can maintain good health as they grow older.
- Chronic low-grade inflammation is a common thread in most chronic diseases
- Chronic inflammation bombardes the body with free radicals that can damage cholesterol and cells
Selenium and hypertension
Elevated blood pressure increases your risk of a heart infarction, stroke (blood clot in the brain or brain hemorrhage), and early death. Oxidative stress, inflammation, and dysfunctions in the endothelial cells are the major causes of elevated blood pressure.
Several studies have shown that patients with elevated blood pressure generate more free radicals and also have a weaker antioxidant defense.
For example, a Chinese twenty-year study (Xie et al.) found that increased intake of selenium was linked to a lower rate of hypertension. However, this was only the case in northern parts of China where the soil is already low in selenium. This is supported by other studies that have shown that selenium supplementation for lowering hypertension is only relevant in populations that are already selenium-deficient.
Selenium requirements and problems with deficiency
Unlike with many other nutrients, the selenium intake varies a lot from country to country and that is primarily due to the large global variations in the selenium content in the soil. European farmland is very low in selenium. Therefore, an average European only gets 40 micrograms of dietary selenium, while most Americans get more than 100 micrograms per day. Available data suggests that the selenium intake is also low in China, Asia, the Middle East, and Africa.
The official recommendations for selenium intake are between 55-70 micrograms per day. This recommendation, according to the new study, is based on the amount of selenium it takes to saturate the selenium-containing GPX antioxidant in the blood. Other research, however, shows that we need more than 100 micrograms of selenium per day to properly saturate selenoprotein P, which is a selenium-carrying protein that is used as a marker to gauge the body’s general selenium status. In any case, it is vital to get enough selenium to saturate all the essential selenoproteins that are found in different tissues. Many studies have tested daily doses of 200 micrograms. The European Food Safety Authority (EFSA) has established a safe upper intake level of 300 micrograms per day.
Jing Huang et al. Selenium Status and Its Antioxidant Role in metabolic Diseases. Oxidative Medicine and Cellular Longevity. 2022
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