New Delhi, Jan. 30: India plans to launch its first giant population study that will track the health of about 15,000 healthy people above 50 for at least five years to pinpoint the risk factors for stroke and cognitive decline.

The study, to be jointly conducted by the All India Institute of Medical Sciences here and Erasmus University in the Netherlands, will seek to identify India-specific factors that can influence these two ailments.

“The incidence of stroke in India appears to be different from that in the West,” said Kameshwar Prasad, a senior neurologist at AIIMS and the study’s principal investigator.

“About half of stroke cases we see in India can’t be explained through known risk factors.”

High blood pressure, smoking and diabetes are among factors known to increase the risk of a stroke, a condition in which the blood supply to a region of the brain is obstructed or a blood vessel in the brain bursts.

Medical surveys in the past have indicated that the incidence of stroke in India ranges from about 155 to 170 per 100,000 people per year, which is significantly higher than the range of 107 to 112 per 100,000 people observed in Caucasian populations.

The planned population study, Prasad said, will seek to unravel the multiple influences — genetic, environmental and lifestyle-related — that may contribute to the risk of stroke and cognitive decline (loss of intellectual capacity through brain dysfunction).

“It is possible that certain factors unique to India, such as food habits and cultural traditions, may also influence the risk,” Manjari Tripathi, a neurologist at AIIMS and co-investigator of the study, told The Telegraph.

Laboratory-based experiments with animals as well as observations of older adults in the past had suggested that social isolation increases the risk of cognitive decline, and high levels of social activity reduce the risk.

This population study, Tripathi said, will provide researchers an opportunity to test the theory that India’s cultural tradition of children staying with their parents and grandparents in the same house may reduce the risk of age-associated cognitive decline.

India’s department of biotechnology will fund the AIIMS study, which will borrow the expertise of Erasmus University scientists who have been running a similar population health study involving about 8,000 people for the past 25 years.

Researchers at AIIMS and the National Brain Research Centre, Manesar (Haryana), will look for 7,500 volunteers from Delhi and 7,500 volunteers from rural Haryana, and track their health through a series of start-of-study blood tests and magnetic resonance imaging (MRI) scans.

The study, likely to begin later this year, will also document their food habits, lifestyles and family histories of illnesses, follow them up every six months through a phone call, and invite them to a repeat health test once every three years.

The researchers hope to be able to continue the study beyond the minimum five years and as long as they can follow up the volunteers.

“The aim of such a study would be to identify biomarkers or indicators on (MRI) images that might help predict disease early,” said Gabriel Krestin, a radiologist at the Erasmus University Medical Centre, where scientists have documented more than 10,000 MRI images of the study volunteers in the Netherlands.

“We expect that our Dutch collaborators will also gain from this study,” Prasad said.

“The influence of certain factors such as vegetarianism on stroke or the effect of illiteracy on cognitive decline could be tested in India much more easily than in Europe.”