By Stephen Daniells, 13-Feb-2007
Related topics: Research, Minerals, Cognitive and mental function
Low levels of selenium throughout life have been linked to lower cognitive function, says an epidemiological study based in China.
The epidemiological study, published in the current issue of the American Journal of 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 increased long-term selenium intake may slow this decline.
“Selenium exposure, unlike other factors studied for Alzheimer’s disease, is a factor that is easily modifiable by changing dietary habits or through supplements,” lead author Sujuan Gao from Indiana University told NutraIngredients.com.
“Our current results provide evidence supporting long-term selenium as a protective agent against cognitive decline. A preventive measure on cognitive decline, even moderate, can have a significant impact on public health by reducing prevalent cases of cognitive impairment, thus reducing the cost of treating and caring for the impaired,” said Gao.
“Most importantly, preventive measures for cognitive decline can prolong the state of healthy aging and maintain the quality of life for many elderly individuals.”
The results may also be important in Europe where 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.
Two thousand elderly Chinese people (average age 72, 54 per cent female) were recruited for the study. Over 70 per cent of the study participants had lived in the same village all their lives.
Mental function was assessed using a battery of tests, including the Community Screening Instrument for Dementia (CSID), the Consortium to Establish a Registry for Alzheimer’s Disease (CERAD) Word List Learning Test, the CERAD World List Recall Test, the Indiana University Story Recall Test, the Animal Fluency Test, and the Indiana University Token Test.
A validated food frequency questionnaire (FFQ) was completed to assess selenium intake from foods such as grains, vegetables, seafood, nuts, fruit, oil, and meat. Nail and blood samples were taken to measure selenium levels of the population, and the population divided into five groups (quintiles) depending on nail selenium levels.
“In this cross-sectional survey of cognitive function in rural elderly Chinese, we found that decreasing selenium levels measured in nail sample are associated with lower cognitive scores when controlling for age, gender, education, body mass index, and ApoE status,” wrote Gao.
“The effect of the lowest selenium quintile [0.232 micrograms per gram or less] compared with the highest quintile [at least 0.553 micrograms per gram] on the CSID score is equivalent to an increase of 10 years in age in this cohort.”
The researchers said that the importance of lifelong selenium intake may be important, with studies having shown that the areas of the brain that take the longest to mature are the same as those that show early signs of Alzheimer’s.
“This suggests that long-term exposure to selenium may be needed to impact brain function later in life,” they said.
They also noted that the brain’s unique way of metabolizing selenium may make it difficult for short-term interventions to impact in long-term brain function.
The research echoes that of a recent study by scientists from the University of Montpellier in France who reported cognitive decline was associated with decreases of plasma selenium over time for the 1389 older subjects aged between 60 and 71 at the start of the study (Epidemiology, Volume 18, Pages 52-58).
Alzheimer’s is the most common form of dementia and currently affects over 13 million people worldwide. The direct and indirect cost of Alzheimer care is over $100 bn (€ 81 bn) in the US alone. The direct cost of Alzheimer care in the UK was estimated at £15 bn (€ 22 bn).
By the year 2047, the prevalence of Alzheimer’s disease (AD) is expected to quadruple.
Source: American Journal of Epidemiology
Published on-line ahead of print, doi:10.1093/aje/kwk073
“Selenium Level and Cognitive Function in Rural Elderly Chinese”
Authors: S. Gao, Y. Jin, K.S. Hall, C. Liang, F.W. Unverzagt, R. Ji, J.R. Murrell, J. Cao, J. Shen, F. Ma, J. Matesan, B. Ying, Y. Cheng, J. Bian, P. Li and H.C. Hendrie