The epidemiological study, published in the current issue of the journal Epidemiology, could help further increase public awareness of a mineral already associated with reducing the risk of prostate and lung cancer, as well as boosting the immune system.
Cognitive performance declines naturally with age, but the results of the longitudinal study suggest that this may be slowed by selenium supplementation.
"Because brain oxidative stress is a cause of cognitive impairment, selenium, which is an antioxidant, may protect against cognitive decline," wrote lead author N. Tasnime Akbaraly, from the University of Montpellier 1.
The results are particularly important because European selenium levels have been falling since the EU imposed levies on wheat imports from the US, where soil selenium levels are high. As a result, average intake of selenium in the UK has fallen from 60 to 34 micrograms per day, leading to calls from some to enrich soil and fertilizers with selenium to boost public consumption.
The European recommended daily intake (RDI) is 65 micrograms.
The European market for selenium supplements is estimated to be worth around €40m. This suggests that there is potential for food makers if they can improve consumer understanding of the mineral's benefits, with selenium-enriched products largely ignored by companies, unlike the supplements where a significant number of selenium products are available, both in combination with other nutrients and alone.
Akbaraly and co-workers recruited 1389 older subjects aged between 60 and 71 at the start of the study and investigated changes in their cognitive function and selenium levels. The average baseline blood selenium level was 1.09 micromoles per litre, and levels were found to generally decrease during the nine years of follow-up.
Adjusting the results for potential confounders, the researchers report that cognitive decline was associated with decreases of plasma selenium over time.
"Among subjects who had a decrease in their plasma selenium levels, the greater the decrease in plasma selenium, the higher the probability of cognitive decline," said Akbaraly. "Among subjects who had an increase in their plasma selenium levels, cognitive decline was greater in subjects with the smallest selenium increase."
"Selenium status decreases with age and may contribute to declines in neuropsychologic[al] functions among aging people," concluded the researchers.
Further research is required, said the researchers, particularly a randomised controlled trials in humans, to further confirm these results. "This dynamic approach could shed new light on the potential benefits of supplementation," said Akbaraly.
Such is the interest in dietary approaches to improve brain health the world's largest food company, Nestlé, recently signalled its intention to get a head start on the competition with the signing of an agreement in November 2006 with the Swiss Federal Institute of Technology (EPFL) to investigate the role of nutrition in cognitive function.
The agreement with the EPFL, Nestlé's largest collaboration with a university of research institute, will see the company contributing up to CHF 5 million (€ 3.1 million) every year for five years, with a review after four years to potentially extend the project further.
Source: Epidemiology January 2007, Volume 18, Number 1, Pages 52-58 "Plasma Selenium Over Time and Cognitive Decline in the Elderly" Authors: N.T. Akbaraly, I. Hininger-Favier, I. Carriere, J. Arnaud, V. Gourlet, A-M. Roussel, C. Berr