NEW YORK (Reuters Health) - A high concentration of silica in drinking water seems to protect against Alzheimer's disease, a study in France suggests. 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 investigators report in the American Journal of Clinical Nutrition.

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.

SOURCE: American Journal of Clinical Nutrition, April 2005.