Selenium is a trace element, or nutrient, that humans need to stay healthy. It plays a role in many bodily processes, including:

• reproduction
• the function of the thyroid gland
• production of DNA
• protecting the body from free radicals, which are unstable cells that move around the body and can increase the risk of diseases, including cancer
• protecting the body from infection

The amount of selenium people need depends on their age. Other factors include whether they are pregnant, or if they are breastfeeding. According to the National Institutes of Health (NIH), the recommended daily amountsTrusted Source are:

• birth to 6 months: 15 micrograms (mcg)
• infants 7–12 months: 20 mcg
• children 1–3 years: 20 mcg
• children 4–8 years: 30 mcg
• children 9–13 years: 40 mcg
• teenagers 14–18 years: 55 mcg
• adults: 55 mcg
• a person who is pregnant: 60 mcg
• a person who is breastfeeding: 70 mcg

Selenium deficiency is rare in the United States. However, it can happen, and can lead to:

• Keshan disease, which is a type of heart disease
• infertility in men
• Kashin-Beck disease, which is a type of arthritis that affects the joints

Scientists are currently investigatinglinks between selenium deficiencies and:

• cancer
• cardiovascular disease
• cognitive decline, which includes problems with memory, problem-solving, and concentration
• cardiovascular disease
• thyroid disease

It is worth noting that too much selenium can be harmful. Over time, it can lead to:

• bad breath
• nausea
• diarrhea
• rashes
• irritability
• a metallic taste in the mouth
• discoloration of the teeth
• brittle hair and nails
• hair loss

The upper limit of selenium also depends on a person’s age. The NIH offers the following advice:

• birth to 6 months: no more than 45 mcg per day
• infants 7–12 months: no more than 60 mcg per day
• children 1–3 years: no more than 90 mcg per day
• children 4–8 years: no more than 150 mcg per day
• children 9–13 years: no more than 280 mcg per day
• teenagers 14 and older, and adults: no more than 400 mcg per day