Selenium is a nutritionally essential element that is critical for many biochemical actions within the human body. It has been shown to help support thyroid health, antioxidative status, and DNA synthesis. Selenium also plays a role in human development, the central nervous system, and cognitive health. A systematic review and meta-analysis published by Pereira and colleagues explored recent literature on the potential link between selenium supplementation and cognitive impairment or Alzheimer’s disease (AD).  

In the body, selenium is most often attached to other structures such as methionine; these are called selenoproteins. Animal studies involving the depletion of selenoprotein P (SELP) reported impaired motor coordination, cognitive decline, irreversible brain damage, and increased risk of seizures. A clinical study observed significantly lower selenium levels in plasma, serum, and erythrocytes in individuals with AD as compared to age-matched healthy controls. A similar study in patients with AD reported decreased selenium levels in circulatory, erythrocyte, and cerebrospinal fluid. Pereira and colleagues observed that the selenium levels of individuals with AD and mild cognitive impairment included in their meta-analysis were below ideal.   

Pereira and colleagues described studies showing that selenium supplementation significantly increased levels of selenium in plasma, serum, erythrocytes, and cerebrospinal fluid. Selenium supplementation was also reported to help improve glutathione peroxidase activity and malondialdehyde levels, an indicator of antioxidative status.  

In studies related to cognitive performance, improvements in cognitive function tests including the Mini-Mental State Examination (MMSE), the Controlled Oral Word Association Test-Verbal Fluency (COWAT), and the Alzheimer’s Disease Assessment Scale-Cognitive subscale (ADAS-Cog) were administered after selenium supplementation for a period of time between 12 and 24 weeks. Improvements in all of these cognitive tests were observed after the selenium treatment period.  

The authors concluded that selenium supplementation may help support cognitive health in the presence of AD or mild cognitive impairment. However, more than 1,300 scientific articles were considered, but only 11 articles met the criteria for systematic review and 6 for the meta-analysis. In addition, some of the studies that were included assessed the efficacy of supplementation with selenium, plus other nutraceuticals. More clinical studies with selenium-only supplementation and increased numbers of participants need to be performed before conclusions can be made.  

Selenium obtained through diet or supplementation may support antioxidative status, cellular health, and thyroid function. Recent research suggests that selenium may also support cognitive health. Selenoproteins, such as selenomethionine, have been shown to have relatively high bioavailability. Dietary sources of selenium include Brazil nuts, organ meats, certain fish, grains, and dairy products. 

By Colleen Ambrose, ND, MAT