"These results are significant because it's possible that if we can reduce or eliminate heavy smoking and drinking, we could substantially delay the onset of Alzheimer's disease for people and reduce the number of people who have Alzheimer's at any point in time," said study author Ranjan Duara, MD, of the Wien Center for Alzheimer's Disease at Mount Sinai Medical Center in Miami Beach, FL, and Fellow of the American Academy of Neurology.

"It has been projected that a delay in the onset of the disease by five years would lead to a nearly 50-percent reduction in the total number of Alzheimer's cases," said Duara. "In this study, we found that the combination of heavy drinking and heavy smoking reduced the age of onset of Alzheimer's disease by six to seven years, making these two factors among the most important preventable risk factors for Alzheimer's disease."

The study looked at 938 people age 60 and older who were diagnosed with possible or probable Alzheimer's disease. The researchers gathered information from family members on drinking and smoking history and determined whether the participants had the epsilon 4 gene variant of the APOE gene, which increases the risk of Alzheimer's disease. People with the epsilon 4 variant also develop Alzheimer's at an earlier age than those who do not have the gene variant.

Seven percent of the study participants had a history of heavy drinking, which was defined as more than two drinks per day. Twenty percent had a history of heavy smoking, which was defined as smoking one pack of cigarettes or more per day. And 27 percent had the APOE epsilon 4 variant.

Researchers found that people who were heavy drinkers developed Alzheimer's 4.8 years earlier than those who were not heavy drinkers. Heavy smokers developed the disease 2.3 years sooner than people who were not heavy smokers. People with APOE epsilon 4 developed the disease three years sooner than those without the gene variant.

Adding the risk factors together led to earlier onset of the disease. People who had all three risk factors developed the disease 8.5 years earlier than those with none of the risk factors. The 17 people in the study with all three risk factors developed Alzheimer's at an average age of 68.5 years; the 374 people with none of the three risk factors developed the disease at an average age of 77 years.

The study was supported by the Florida Department of Elder Affairs.

The American Academy of Neurology, an association of more than 21,000 neurologists and neuroscience professionals, is dedicated to improving patient care through education and research. A neurologist is a doctor with specialized training in diagnosing, treating and managing disorders of the brain and nervous system such as Alzheimer's disease, epilepsy, multiple sclerosis, Parkinson's disease, and stroke.

For more information about the American Academy of Neurology, visit www.aan.

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