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 The study team followed two groups of dementia-free adults aged 65
to 74 years for up to 15 years. One group, considered healthy,
included 257,523 non-smokers who didn't have cancer, heart failure
or multiple chronic health problems; another group of 161,927
adults, deemed unhealthy, did smoke or have serious chronic medical
issues.
Over the first decade of the study, healthy people who were obese or
overweight were less likely to develop dementia than healthy people
at a normal weight, the study found. But after that, obesity was
associated with a 17 percent higher risk of dementia and being
heavier no longer appeared to be protective.
"When we looked long-term, being obese was definitely associated
with increased risks of dementia," said senior study author David
Melzer of the University of Exeter in the UK.
People with obesity often have other health problems like diabetes
and high blood pressure that can independently increase the risk of
dementia, previous research has found. But results regarding the
connection between obesity and dementia have been mixed, with some
previous studies suggesting that this excess weight might actually
be protective.
In the current study, 9,774 people in the "healthy" group were
diagnosed with dementia. Slightly more than half of the dementia
patients had lost at least 2.5 kilograms (5.5 pounds) during the
decade prior to their diagnosis.
Weight loss prior to the dementia diagnosis might mask the
connection between obesity and cognitive decline, Melzer said by
email.
Alzheimer's disease, the main cause of dementia, can develop slowly
over up to 20 years before people get diagnosed, Melzer noted.
"The same is true of damage to the arteries in the brain, which also
contributes to dementia," Melzer said. "This slow development of
dementia makes it difficult to separate real risk factors from the
effects of the disease."
Interestingly, obesity was associated with a lower short-term and
long-term risk of dementia for the unhealthy group in the study. A
total of 6,070 individuals in the unhealthy group developed
dementia.
"In general, losing weight, being more physically active, and
getting blood pressures and cholesterol levels under control should
make a big difference for dementia risk, plus risks of diabetes and
heart disease," Melzer said.
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The study wasn't designed to prove whether or how obesity might
directly cause dementia in later years. Another limitation is that
researchers lacked data to examine the connection between obesity
and specific forms of dementia like Alzheimer's disease, the authors
note in Age and Ageing.
In a separate study in the same journal, researchers led by
Alexander Allen of the London School of Hygiene and Tropical
Medicine also examined the connection between overweight and
dementia, and also cast doubt on the idea that obesity is
protective.
The researchers analyzed the link between excess belly fat in middle
age and the risk of death from dementia over the next 40 years in
about 19,000 male civil servants participating in a long-term health
study.
They found that weight loss over 30 years, starting in middle age,
was associated with an increased risk of dementia in old age. Having
excess fat in old age, however, was tied to a lower risk of
dementia.
While that may appear to suggest a protective effect of extra
weight, in fact, the strongest connection, between weight loss over
time and an eventual dementia diagnosis, points to the symptoms of
developing dementia contributing to the weight loss, Allen and
colleagues write.
"These effects may reflect changes in appetite or other aspects of
behavior that result in reduced energy intake," they note. "Thus,
claims from previous studies that underweight increases the risk of
dementia may be an artefact of the effects of reverse causality."
Allen didn't respond to requests for comment.
"Regular weight checks could provide an easily measured marker for
risk of frailty and subsequent detection of dementia," Allen and
colleagues write. "Whether this could allow early interventions to
improve dementia outcomes could also merit further investigation."
SOURCE: https://bit.ly/2C9klwR Age and Ageing, online February 6,
2019 and https://bit.ly/2TD4iRN Age and Ageing, online January 9,
2019.
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