The study, which shows correlation and not causation, also suggested that the association between selenium status and the risk of depressive symptoms was U-shaped, meaning that too low and too high levels of the trace mineral may detrimentally affect mood.
“In young adults, an optimal range of serum selenium between about 82 and 85 micrograms per liter was associated with reduced risk of depressive symptomatology,” wrote the researchers in the Journal of Nutrition.
“This range approximates the values at which glutathione peroxidase is maximal, suggesting that future research should investigate antioxidant pathways linking selenium to mood.”
Selenium facts
Selenium is an essential micronutrient, and is considered to be an antioxidant. High levels of selenium have been inversely associated with risk of developing several cancers, including bladder, prostate and thryroid.
The mineral is included in between 50 and 100 different proteins in the body, with multifarious roles including building heart muscles and healthy sperm. However, cancer prevention remains one of the major benefits of selenium, and it is the only mineral that qualifies for a Food and Drug Administration (FDA)-approved qualified health claim for general cancer reduction incidence.
A review paper by Joyce McCann and Bruce Ames from the Nutrition and Metabolism Center at Children’s Hospital Oakland Research Institute in Oakland (CHORI) indicated that moderate deficiency in selenium may have long-term detrimental effects (FASEB Journal, 2011, Vol. 25, pp. 1793-1814).
Study details
Tamlin Conner, Aimee Richardson, and Jody Miller from the University of Otago in New Zealand now report that the micronutrient may also play a role in mood in young people.
Data from 978 adults aged between 17 and 25 was analyzed by the researchers using the Center for Epidemiological Studies–Depression scale. Mood was also recorded for 13 days using an Internet diary.
Statistical analysis indicated that, for the lowest incidence of depressive symptoms, the ‘sweet spot’ selenium concentration was between 82 and 85 micrograms per day.
The association was U-shaped, they added, with people with the lowest and highest average levels (62 and 110 micrograms per day, respectively) having “significantly greater adjusted depressive symptoms than did participants with midrange serum selenium concentrations”.
The researchers also noted that the greatest symptoms of depression were observed for the lowest levels, leading them to suggest that the lower levels were more detrimental than the higher levels.
“This is the first study to demonstrate that both low and high selenium statuses were associated with increased depressive symptomatology within the same sample of young adults,” they wrote. “This is also the first study to show that selenium concentration is related to daily negative mood in a similar way to depressive symptoms. Negative mood was also lowest around a selenium concentration of 85 mg/L.”
Biological plausibility?
Commenting on the potential mechanism of action, the researchers said that the micronutrient’s antioxidant activity may be behind the effects.
“At serum selenium concentrations of 70–90 mg/L, plasma [glutathione peroxidase antioxidant enzymes] are functioning at maximum activity levels,” they wrote. “Below this level, the enzymes may not be performing at their maximum and thus the optimal antioxidant protection may not be achieved. This could result in increased vulnerability to oxidative stress and may explain why levels of depressive symptomatology were highest in the lowest decile with serum selenium concentrations [less than] 62 mg/L.
“Moreover, in high doses, selenium has been demonstrated to generate reactive oxygen species (ROS). Although the range at which selenium begins to produce ROS in humans is not yet known, this mechanism could suggest that, in higher doses, selenium may influence depressive symptoms via the generation of ROS leading to oxidative stress.
“Although further research is needed, care should be taken to avoid consuming a diet too low or too high in selenium,” they concluded.
Source: Journal of Nutrition
Published online ahead of print, doi:10.3945/jn.114.198010
“Optimal Serum Selenium Concentrations Are Associated with Lower Depressive Symptoms and Negative Mood among Young Adults”
Authors: T.S. Conner, A.C. Richardson, J.C. Miller