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new, long-term study finds that midlife
obesity raises the risk of dementia in women. However, calorie intake and
physical inactivity do not.
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on PinterestObesity in midlife may raise a woman's risk of dementia later on,
new research suggests.
Sarah Floud, Ph.D., of the Nuffield
Department of Population Health at the University of Oxford in the United
Kingdom, is the lead author of the study.
As Floud and her colleagues explain
in their paper, some previous studies have found an association between a low
body mass index (BMI) and the likelihood of receiving a
diagnosis of dementia within the
next 5–10 years.
Other studies that lasted a decade
or less have also linked poor diet and lack of exercise with the incidence of
dementia.
However, all of the above may be the
result of reverse causality, meaning that they may be consequences, rather than
causes, of dementia. This situation could well be possible, explain the
authors, because dementia typically affects cognition a decade before the
person formally receives a diagnosis.
During this preclinical stage, the
condition can slowly but gradually affect behavior, impair mental and physical
activity, reduce the intake of food and calories, and cause weight
loss.
Furthermore, explain the authors,
some recent meta-analyses have pointed out that although in the short term, a
low BMI may be associated with dementia as a result of reverse causality, over
a longer period, obesity is positively associated with
dementia.
Either way, prospective studies over
longer periods are necessary to settle the matter of how BMI connects to
dementia risk. Floud and her team set out to do exactly this.
Their findings appear in the
journal Neurology.
Studying diet, inactivity, BMI, and dementia
The team examined 1,136,846 women in
the U.K. They had an average age of 56 years and were free of dementia at the
start of the study, between 1996 and 2001.
The women gave information about
their height, weight, calorie intake, and physical activity, and the
researchers clinically followed them until 2017 through the National Health
Service records. These records also noted any hospital admissions for dementia.
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For their study, the scientists
considered a BMI of 20–24.9 as "desirable," 25–29.9 as overweight,
and 30 and over as obese. They classified women who exercised less than once a
week as inactive and those who exercised at least once weekly as active.
Using Cox regression models, the
team calculated the links between BMI and dementia incidence over the follow-up
period, adjusting for age, height, education, smoking, alcohol intake, use of
menopausal hormones, residential area, and area deprivation.
Midlife obesity linked with 21% higher risk
Over the study period, 89% of the
participants had no mention of dementia in their health records. At 15 years
after the start of the study, 18,695 women had received a dementia diagnosis.
Women who had obesity at the beginning
of the study were 21% more likely to develop dementia than women who had a
"desirable" BMI.
More specifically, 2.2% of the women
with obesity went on to develop dementia in the long term, compared with 1.7%
of those with a healthy BMI.
Although the findings revealed that
low calorie intake and a lack of physical activity had a link with higher
dementia risk in the first decade of the study, these associations gradually
faded after that period, and neither calorie intake nor inactivity had a
significant association with dementia risk.
Floud comments on the findings,
saying, "Some previous studies have suggested poor diet or a lack of
exercise may increase a person's risk of dementia."
"However,
our study found these factors are not linked to the long-term risk of dementia.
[...] The short-term links between dementia, inactivity, and low calorie intake
are likely to be the result of the earliest signs of the disease, before
symptoms start to show," she emphasizes.
"On the other hand, obesity in midlife was linked with
dementia 15 or more years later. Obesity is a well-established risk factor
for cerebrovascular disease.
Cerebrovascular disease contributes to dementia later in life."
Sarah Floud, Ph.D.
The study is limited by the fact
that it only involved women, which means that the findings may not apply to
men.
The authors of a linked editorial also mention "the absence of
time-dependent dynamic analyses of BMI [...], crude measurement of dietary
habits, and residual confounding" as study limitations.
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