Selenium is a very important trace mineral and a key component of our natural antioxidant system. The enzymes and proteins it produces help protect our cells from damage and infection. It has been observed that people with better selenium intake have a much lower risk of certain chronic diseases.(1,2,3) However, this is only up to a certain point, after which excessive selenium intake leads to negative effects and increases the risk of type 2 diabetes, among other things.(4,5) As the healthy range for selenium is relatively narrow, we need to be careful not to over-consume it while preventing deficiencies.

Inefficiency of antioxidant supplementation

It has been known for quite some time that high doses of antioxidant supplementation have not always lived up to expectations. This was the case with beta-carotene, which was found to increase the risk of lung cancer instead of reducing it.

The human body functions properly when it has the optimal amount and proportion of the substances it needs. A one-sided, unrealistically high-dose supplementation of an otherwise beneficial nutrient can easily upset this natural balance.

Selenium is needed to produce an enzyme called glutathione peroxidase, which protects cells from lipid peroxidation. Partly for this reason, it has long been thought that higher selenium intake may be protective against cardiovascular and other chronic diseases.

Selenium is only effective in combination with other antioxidants

Supplementation with selenium alone has led to mixed results, but a meta-analysis published in 2020 found that when combined with other antioxidants, it significantly reduces the risk of cardiovascular disease and all-cause mortality(6).

In this study, the results of 43 clinical trials investigating the effects of supplementation with different micronutrients with antioxidant activity (vitamin A, β-carotene, vitamin C, vitamin E, selenium, zinc and copper) on cardiovascular and all-cause mortality were pooled. Although neither selenium nor the other antioxidants were found to be effective on their own, significant risk reductions have been achieved in trials where selenium was used in combination with the above antioxidants.

Selenium, in combination with at least two other micronutrients, has been shown to reduce the risk of cardiovascular death by 23% and the risk of death from any cause by 10%. Zinc and copper, vitamin C, vitamin E and vitamin A all strengthen different parts of the body’s defences, and if one is deficient in one, their whole system can be damaged.

Summary

Special attention should be given to selenium supplementation, as intakes are typically lower than needed. Selenium-rich foods are also usually good sources of zinc and copper, which are also necessary for the functioning of the antioxidant system. When supplementing with selenium, don’t forget other important micronutrients, as in this meta-analysis only their combined supplementation was shown to be effective.