7.23.2004

Developing Alzheimer's linked to lifestyle more than genetics
Research with twins offers hope the disease can be delayed, perhaps prevented

New research conducted on twins provides compelling evidence that lifestyle plays a greater role than genetics in developing Alzheimer's.

The study found that if one identical twin developed Alzheimer's, there was a 40-per-cent chance that the other twin (whose genes are virtually identical) would do the same.

Among fraternal twins, there was a 20-per-cent chance of both developing the devastating neurological condition.

The study, presented yesterday at the International Conference on Alzheimer's Disease and Related Disorders in Philadelphia, involved more than 200 pairs of twins who were veterans of the Second World War.

A second study, using data from the Swedish Twin Registry, found similar results.

Among identical twins, if one twin developed Alzheimer's, 59 per cent of the time the other twin did as well. For same-sex fraternal twins, 32 per cent both got the disease, while among boy-girl fraternal twins, the incidence was 24 per cent.

"These results mean that environment must be helping to explain why one twin develops dementia and the other does not," said Margaret Gatz, a professor of psychology and aging at the University of Southern California in Los Angeles. She conducted the Swedish research.

Brenda Plassman, director of the epidemiology of dementia program at Duke University Medical Center in Durham, N.C., said the new findings are not just a curiosity. Rather, they provide real hope that Alzheimer's can be delayed, and perhaps prevented.

Dr. Plassman cited earlier research that showed delaying the onset of Alzheimer's by just five years could reduce the number of cases by half during the next 50 years.

"Data from these World War II veterans suggest that, even barring any conscious effort to change the course of Alzheimer's, there are environmental factors at work that can affect the age of onset by that critical five-year margin," she said.

Alzheimer's disease is a degenerative brain disorder that destroys vital brain cells. It is characterized by the buildup of plaque in the brain. About 354,000 Canadians suffer from the disease, according to the Canadian Alzheimer Society.

Beyond genetics, a number of factors are believed to contribute to Alzheimer's and related dementias. They include other medical conditions like diabetes and cardiovascular disease, obesity, poor nutrition and head injuries. People with low income, and in certain occupations, are far more likely to develop Alzheimer's. Studies have also shown that people who are mentally active -- doing crossword puzzles, reading and playing games -- are at lower risk.

As the twins are followed into old age, Dr. Plassman said, the weight of these various risk factors will become clearer.

However, the importance of socio-economic determinants of health is already emerging from the new twins research. In particular, researchers found that the higher a person's level of education, the lower the risk of developing Alzheimer's.

"The reason that low education is related to higher risk of Alzheimer's disease appears to a great extent to relate to environmental influences," Dr. Gatz said. In other words, people with higher education are more likely to have a higher income, have a better diet and live in better housing. They are also likely to have more "mental stimulation," Dr. Gatz said, and that may prove to be a key prevention measure.

The conference featured dozens of new studies on factors that influence Alzheimer's. Some of the highlights include:

Eating a diet rich in green vegetables like spinach and broccoli seems to reduce the risk of women developing Alzheimer's, likely because the vegetables are rich in folic acid and antioxidants;

The well-known risk factors for cardiovascular disease -- such as obesity, high blood pressure and high cholesterol -- all appear to also increase the risk of developing Alzheimer's;

Being obese (meaning your body mass index exceeds 30) in middle age more than doubles your risk of developing Alzheimer's later in life;

Stress seems to increase the production of plaque in the brain, and increase the severity of Alzheimer's symptoms;

Almost 40 per cent of elderly people who had not been diagnosed with dementia before they died had changes in their brain characteristic of Alzheimer's disease, a finding that confirms the disease develops many years before symptoms arise;

People with Alzheimer's seem to be less likely to develop cancer.

Alzheimer's is largely age-related: About one in 13 people over the age of 65, and one in four over the age of 85, develop the condition. Two of every three people diagnosed with the disease are women.

There is no single known cause for Alzheimer's disease, and no cure.




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