Selenium is a trace mineral that plays a crucial role in many bodily processes, including producing active thyroid hormones, DNA synthesis, and protecting the body from free radicals, which are unstable atoms that can damage cells, causing illness and aging. It can also help with cognition, immune system function, and fertility.
This nutrient is an essential component of various enzymes and proteins that perform several normal health and metabolism functions. Selenoproteins have an important role in skeletal muscle regeneration, cell maintenance, oxidative and calcium homeostasis, thyroid hormone metabolism, and immune responses. Iodothyronine deiodinases that convert inactive thyroxine (T4) to active thyroid hormone, triiodothyronine (T3), are selenium-dependent.
Due to selenium’s ability to reduce oxidative stress, boost the immune system, reduce DNA damage and oxidative stress, it may help reduce the risk of certain cancers. Epidemiological studies have found a link between low selenium levels and an increased risk of bladder, colorectal, esophageal, gastric, lung, prostate, and skin cancer. A Cochrane review of selenium and cancer prevention studies found a 31% reduced risk of cancer development, a 45% decrease in cancer mortality rate, a 33% reduction in the risk of bladder cancer, and a 22% lower risk of prostate cancer development in men.
The thyroid gland needs selenium to function correctly. Thyroid tissue, in fact, has the highest concentration of selenium of any organ in the body. This vital mineral protects the thyroid from oxidative damage and is required for thyroid hormone synthesis. Selenium deficiency can lead to autoimmune thyroid conditions such as Hashimoto’s disease and Graves’ disease. Both of these disorders cause the body to produce antibodies that attack the thyroid gland, resulting in overactive thyroid (hyperthyroidism) or underactive thyroid (hypothyroidism).
Plants are the primary source of selenium, and their content is determined by the selenium levels in the soil where the food was grown. A lack of selenium has been linked to cardiovascular disease, infertility, myodegenerative diseases, a weakened immune system, cognitive decline, susceptibility to viral infections, and an increased risk of cancer. While a lack of selenium can cause serious health problems, an excess of selenium can also be toxic.
Selenium Sources
Brazil nuts are an excellent source of selenium. Ten grams contain 192 mcg, approximately 349% of your daily value. To avoid selenium toxicity, limit your consumption of Brazil nuts to a few times per week. It can also be present in various fresh foods such as organ meats, shellfish, fish, meat, egg, nuts, and seeds.
Foods High In Selenium
| Food | Microgram (mcg) per 100 grams | Percent DV |
| Brazil Nuts | 1920 mcg | 3490% |
| Kidney | 312 mcg | 567% |
| Oysters | 154 mcg | 280% |
| Liver | 111 mcg | 202% |
| Tuna (Yellowfin) | 108 mcg | 196% |
| Octopus | 89.6 mcg | 163% |
| Mussels | 89 mcg | 162% |
| Sunflower Seeds | 79 mcg | 144% |
| Lobster | 72.6 mcg | 132% |
| Anchovies | 68.1 mcg | 124% |
| Chia Seeds | 55.2 mcg | 100% |
| Mackerel (Atlantic) | 51.6 mcg | 94% |
| Pork Chop | 51 mcg | 93% |
| Salmon (Sockeye) | 35.5 mcg | 65% |
| Shrimp | 32.7 mcg | 59% |
Selenium Recommended Intakes
The amount of selenium you need each day depends on your age, but it is recommended that adults get 55 micrograms per day. Pregnant and lactating females need a slightly higher intake of 60 and 70 micrograms per day, respectively.
Recommended Dietary Allowances (RDAs) For Selenium
| Age | Male | Female |
| 0–6 months | 15 mcg | 15 mcg |
| 7–12 months | 20 mcg | 20 mcg |
| 1–3 years | 20 mcg | 20 mcg |
| 4–8 years | 30 mcg | 30 mcg |
| 9–13 years | 40 mcg | 40 mcg |
| 14–18 years | 55 mcg | 55 mcg |
| 19–50 years | 55 mcg | 55 mcg |
| 51+ years | 55 mcg | 55 mcg |
Selenium Deficiency
Selenium deficiency has been linked to problems with human growth and reproduction. It can cause various symptoms, such as depression, anxiety, confusion, reduced infertility, muscle weakness, fatigue, hair loss, a weakened immune system, increased susceptibility to viral infections, and increased cancer risk.
For adults, the American Recommended Dietary Allowance (RDA) daily minimum requirement of selenium for optimal biological functioning is 55 micrograms per day. Other studies, however, consider this level to be below, and some research sets the minimum requirement at 90 mcg daily per adult. The World Health Organization considers 400 micrograms of selenium per day the tolerable upper intake level for adults 19 and older. Levels higher than this are considered toxic.
Selenium Toxicity
Selenium toxicity can occur due to either acute or chronic selenium overdose. Symptoms of selenium toxicity include a garlicky odor in the breath, nausea, vomiting, hair loss, alopecia, gastrointestinal upsets, mild nerve damage, fatigue, irritability, transverse lines on the nails, nail discoloration, brittleness, and loss. Too much selenium leads to selenosis, a condition that can result in hair and nail loss.
