By Merritt McKinney
NEW YORK, Jan 24 (Reuters Health) -- Having lots of brothers and sisters
may increase the risk of Alzheimer's disease, according to new study findings.
In the study, people with five or more siblings were 39% more likely to develop
the disease, researchers report in the January issue of the journal Neurology.
The study did not examine the reasons for the higher risk, but it might
have something to do with how the brain matures. The brains of children in large
families, which tend to be less financially well-off than smaller families, may
not mature completely, according to Dr. Victoria Moceri, of the University of
Washington in Seattle, and colleagues.
"A poor quality childhood environment could prevent the brain from
reaching a complete level of maturation," she said in a statement. "The effects
of impaired development could produce a brain that is normal, but functions less
efficiently." She noted that these effects might become more apparent once the
aging process begins.
Even though there appears to be a connection between family size and
Alzheimer's disease, Moceri told Reuters Health that it would be a mistake to
conclude that having lots of brothers and sisters means a person will develop
Alzheimer's disease.
"You can't apply it to the individual," she said. "I don't think if
everyone goes out and has two kids, Alzheimer's will disappear." She noted that
many factors, both environmental and genetic, probably contribute to the
disease.
According to Moceri, the most important message from the study is that
environment early in life may play at least a partial role in the risk of
Alzheimer's much later in life. She noted that a child's early environment has
been linked to the risk of a number of chronic diseases such as heart disease,
stroke and diabetes mellitus in adulthood, but these diseases usually begin much
earlier than Alzheimer's.
The study included 393 people with Alzheimer's disease and 377 people who
did not have the disease. All participants, who were members of a health
maintenance organization, were aged 60 or older.
Moceri and her colleagues found that the risk of Alzheimer's increased by
8% for each additional sibling in a family. Besides family size, area of
residence during childhood was also related to the risk of Alzheimer's. People
who grew up in suburbs, rather than in urban areas or on farms, were less likely
to have the disease.
Since suburbs tended to be sparsely populated and to have relatively
prosperous residents in the early 1900s, when the participants were children,
the researchers state that the lower risk "could reflect the benefits of higher
socioeconomic status and less exposure to infectious disease." However, they did
not detect a protective effect of living on farms, where exposure to infection
would be expected to be lower. But Moceri and her colleagues do note that many
farm families during this era moved to urban areas when their farms failed.
