Study participants who were overweight or obese in midlife developed Alzheimer's an average of 6.7 months earlier than those of a healthy weight.
Common risk factors for Alzheimer's include age, a family history of the disease and the presence of certain genes, such as apolipoprotein E-e4 (APOE-e4).
Previous studies have also suggested a link between midlife obesity and increased risk for Alzheimer's, but study co-author Dr. Madhav Thambisetty, of the Laboratory of Behavioral Neuroscience at the National Institute on Aging (NIA), and colleagues say it was unclear how midlife obesity impacts the age of onset. They set out to assess this association with their latest research.
The study involved the analysis of 1,394 cognitively normal adults who were a part of the Baltimore Longitudinal Study of Aging (BLSA) - one of the longest-running longitudinal studies of aging in the US.
The team assessed participants' body mass index (BMI) at midlife - defined as the age of 50 - and their development of Alzheimer's via neurological assessments every 2 years for an average of 14 years. During follow-up, 142 participants developed Alzheimer's.
The higher BMI is in midlife, the earlier the onset of Alzheimer's
The researchers found that subjects who were overweight or obese in midlife - defined as having a BMI of 25 or over - were likely to develop Alzheimer's around 6.7 months sooner than participants of a healthy weight.
What is more, the risk of earlier Alzheimer's onset rose with each unit increase in midlife BMI. For example, participants with a BMI of 30 in midlife were likely to develop Alzheimer's a year earlier than those with a BMI of 28.
The researchers also assessed two subsamples from the BLSA, involving 191 deceased subjects who underwent autopsy and neuropathological assessment.
From this, the team found individuals with a high BMI in midlife were more likely to have greater abundance of amyloid proteins in the brain, a hallmark of Alzheimer's. This was true even for subjects who were free of dementia.
While the researchers are unable to describe the exact mechanisms behind their findings, they believe their results highlight the importance of maintaining a healthy weight in midlife in order to prevent early Alzheimer's onset. They add:
"Our findings raise the possibility that inexpensive, noninvasive interventions targeting midlife obesity and overweight could substantially alter the trajectory of Alzheimer's disease, reducing its global public health and economic impact."
The team notes that further research involving a larger study sample is warranted in order to determine whether there is a specific BMI value at which the risk of earlier Alzheimer's onset begins to increase.
Last month, Medical News Today reported on a study by Canadian researchers that found an abnormal accumulation of fat in the brain may speed up the progression of Alzheimer's.