Dr. Sophie Gillette-Guyonnet, at Hopital Casselardit in Toulouse, and colleagues studied women enrolled in the Epidemiology of Osteoporosis Study (EPIDOS). The subjects included 7598 women older than 75 years from five cities in France, whose mental acuity was measured at the start of the study between 1992 and 1994.
Their intake of water (tap versus mineral water) was ascertained by questionnaire, and data on levels of silica, calcium, and aluminum were obtained from local water companies and companies distributing mineral water.
Women with normal or higher mental function at the outset had a higher daily silica intake, The relationship remained statistically significant after taking account of age, location, income, educational level and history of stroke.
In a second phase of the study, women living in Toulouse who had normal or higher cognitive scores were followed for up to seven years. During that time, 60 women developed Alzheimer's disease while 323 maintained normal cognitive function.
The women with Alzheimer's disease were 2.7 times more likely to have daily silica intake considerably lower than those without Alzheimer's disease, the researchers found. They suggest that silica is a "natural antidote" to aluminum, which has been linked to the formation of so-called senile plaques in the brain. However, in the current study there appeared to be no relationship between aluminum in drinking water and cognitive function -- but levels of aluminum in the groups studied were very low.
Background: The concentration of aluminum or silica in drinking water may be a potential environmental risk factor for Alzheimer disease (AD).
Objectives: The objective was to investigate at baseline the potential association between the composition of drinking water and the level of cognitive function in women taking part in the Epidemiology of Osteoporosis (EPIDOS) Study and to determine during follow-up the effects of the composition of drinking water on the risk of AD.
Design: Women aged 75 years (n = 7598) were recruited between 1992 and 1994 in 5 geographic areas of France. The participants from one center (n = 1462) were followed for 7 years; during this time, an active search for incident cases of Alzheimer's Disease was conducted. The initial questionnaire comprised a food consumption survey with specific questions about the daily consumption of tap and mineral water. The evaluation of cognitive function was based on the Short Portable Mental Status Questionnaire. During follow-up, the diagnosis of dementia was made by a geriatrician and a neurologist.
Results: A low silica concentration was associated with low cognitive performance at baseline. Compared with the nondemented subjects, the women with a diagnosis of Alzheimer's Disease during follow-up were older at inclusion, had a lower financial status and educational level, had a poorer perception of their own health, and had a more difficult time performing activities of daily living. A multivariate analysis including potential confounding factors showed that women with AD appeared to have been exposed to lower amounts of silica at baseline.
Conclusions: Silica in drinking water may reduce the risk of developing Alzheimer's Disease in elderly women. The results corroborate those of another epidemiologic study carried out in France. The potential effect of silica needs to be confirmed in additional investigations.
Sophie Gillette-Guyonnet, Sandrine Andrieu, Fatemeh Nourhashemi, Viviane de La Guéronnière, Hélène Grandjean and Bruno Vellas; Cognitive impairment and composition of drinking water in women: findings of the EPIDOS Study; American Journal of Clinical Nutrition, Vol. 81, No. 4, 897-902, April 2005.