The cause of Alzheimer’s disease is unknown, but various studies suggest that its risk factors extend beyond genetics. Some studies have associated the disease with a dearth of physical activity. Others have linked Alzheimer’s disease to a lack of stimulating brainwork–fitting a use-it-or-lose-it scenario of cognitive decline.
A new study bolsters the view that both kinds of inactivity pose risks. People who have the memory loss, confusion, and disorientation of Alzheimer’s disease in old age were generally less active physically and intellectually between the ages of 20 and 60 than were people who don’t have the disease, according to study coauthor Robert P. Friedland, a neurologist at Case Western Reserve University School of Medicine in Cleveland, and his colleagues.
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The researchers collected lifestyle histories of 193 Alzheimer’s patients with an average age of 73. The scientists compared these with data on a control group of 358 people, average age 71, without Alzheimer’s.
The team then calculated the amount of leisure time each participant had spent between ages 20 and 60 on each of three types of activities. Passive activities included watching television, talking on the phone, and going to church. The scientists also tallied time spent on intellectual activities, such as reading, knitting, and playing a musical instrument, and on physical activities that included gardening, walking, and competitive sports.
The researchers tabulated how many different passive, intellectual, or physical pursuits each person performed, hours spent on them, and the percentage of leisure time devoted to each.
After establishing an average overall activity level for all the study’s participants, the researchers discovered that the Alzheimer’s patients were nearly four times as likely as the people without Alzheimer’s to fall below that average. In particular, the non-Alzheimer’s volunteers had devoted more time on average between ages 40 and 60 to intellectual activities and less to passive ones than had those who developed the disease. The researchers report their findings in the March 13 Proceedings of the National Academy of Sciences.
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The only single activity in which Alzheimer’s patients on average significantly outperformed their counterparts was watching television, Friedland says.
While certain genetic factors seem to influence the brain deterioration associated with Alzheimer’s, these don’t account for all cases of the disease. Indeed, studies of genetically similar people living in separate countries show divergent rates of Alzheimer’s disease.
The new study accounted for differences in education and income but not occupation. It doesn’t point to a cause of Alzheimer’s or even predict who might develop the disease, but it does reinforce the value of remaining physically and mentally active, Friedland says. From an evolutionary standpoint, people are still physically designed to be active hunters and gatherers. “Being a couch potato,” he says, “is not our natural state.”
Intellectual stimulation may work the same way, he says. Studies indicate that a higher educational level makes a person less likely to develop Alzheimer’s disease. Some researchers suggest that challenging the brain builds reserves of functional brain tissue that protect people against the disease.
“This is a very intriguing study” built on “extremely rigorous” data collection and tabulation, says Mary S. Mittelman, an epidemiologist at New York University School of Medicine. However, she wonders why some people are active during their middle years while others aren’t. Could it be that a sedentary lifestyle really contributes to the development of Alzheimer’s, or does the ailment begin early in life and subtly steer a person toward such a lifestyle?
“It could be a combination of both,” Friedland says.