The study found that the risk of developing Alzheimer's increases by eight percent for each additional sibling in the family. Those growing up with five or more siblings have a 39-percent greater risk of developing the disease than those with fewer than five siblings.

The study examined 770 people age 60 and older who were members of a large health maintenance organization in Seattle, Wash. Of the participants, 393 had Alzheimer's disease and 377 had no signs of dementia.

Researchers looked at whether any environmental factors in the participants' childhood were related to developing Alzheimer's. "The early-life environment and its effect on the growth and maturation of children is linked to many adult diseases, such as heart disease, stroke and diabetes," said study author Victoria Moceri, PhD, of the University of Washington. "We wanted to test whether Alzheimer's may also have a link to the early-life environment."

The areas of the brain that show the earliest signs of Alzheimer's are the same areas of the brain that take the longest time to mature during childhood and adolescence, Moceri said. "A poor quality childhood environment could prevent the brain from reaching a complete level of maturation," she said. "The effects of impaired development could produce a brain that is normal, but functions less efficiently."

Moceri said the negative effects of this less efficient brain would likely be marginal until they were aggravated by the aging process.

"Families with five or more children were more likely to be from the lower socioeconomic levels, and therefore more likely to have poor growth rates," Moceri said. Researchers also found that children who grew up in the suburbs were less likely to develop Alzheimer's than those who grew up on farms or in the city.

Moceri noted that suburbs in the early 1900s when these people were growing up were sparsely populated.

"This could reflect the benefits of higher socioeconomic status and less exposure to infectious disease," Moceri said. "During the early 1900s, infectious diseases were more frequent in urban areas than in less densely populated areas. Children growing up in the suburbs may have been more likely to have better nutrition and less exposure to infectious disease, leaving more energy for normal growth and development.

"But, following this logic, we expected to find that children who grew up on farms were less likely to develop the disease than those who grew up in the city, and that wasn't the case. But many farming families during this era experienced economic difficulties and left their farms for jobs in the city. We weren't able to separate out those who grew up on successful farms and those who came from families that lost their farms, so we weren't fully able to test that hypothesis." Researchers also examined the mother's age at the child's birth and the birth order within the family and found no relationship between those factors and whether the child developed Alzheimer's disease.

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The study was supported in part by grants from the National Institute on Aging.

A neurologist is a medical doctor with specialized training in diagnosing, treating and managing disorders of the brain and nervous system.

The American Academy of Neurology, an association of more than 16,000 neurologists and neuroscience professionals, is dedicated to improving patient care through education and research.

For more information about the American Academy of Neurology, visit its Web site at http://www.aan.com. For online neurological health and wellness information, visit NeuroVista at http://www.aan.com/neurovista.

Note: If no author is given, the source is cited instead.

• Alzheimer's Research
• Healthy Aging

• Alzheimer's
• Dementia

• Dementia with Lewy bodies
• Dementia
• Occupational therapy
• Mental retardation
• Brain damage
• Multi-infarct dementia