Summary: A higher BMI and bigger waist during your sixties have been linked to an increase in cortical thinning. Having a thinner cortex has previously been associated with an increased Alzheimer’s risk.
Having a bigger waistline and a high body mass index (BMI) in your 60s may be linked with greater signs of brain aging years later, according to a study published in the July 24, 2019, online issue of Neurology. The study suggests that these factors may accelerate brain aging by at least a decade.
“People with bigger waists and higher BMI were more likely to have thinning in the cortex area of the brain, which implies that obesity is associated with reduced gray matter of the brain,” said study author Tatjana Rundek, MD, PhD, of University of Miami Miller School of Medicine and a member of the American Academy of Neurology. “These associations were especially strong in those who were younger than 65, which adds weight to the theory that having poor health indicators in mid-life may increase the risk for brain aging and problems with memory and thinking skills in later life.”
The study involved 1,289 people with an average age of 64. Two-thirds of the participants were Latino. Participants’ BMI and waist circumference were measured at the beginning of the study. An average of six years later, participants had MRI brain scans to measure the thickness of the cortex area of the brain, overall brain volume and other factors.
A total of 346 of the participants had a BMI of less than 25, which is considered normal weight; 571 people had a BMI of 25 to 30, which is considered overweight; and 372 people had a BMI of 30 or higher, which is considered obese.
For waist circumference, which can be different for men and women, the normal weight group, which was 54 percent women, had an average of 33 inches. The overweight group, which was 56 percent women, had an average of 36 inches, and the obese group, which was 73 percent women, had an average of 41 inches.
Having a higher BMI was associated with having a thinner cortex, even after researchers adjusted for other factors that could affect the cortex, such as high blood pressure, alcohol use and smoking. In overweight people, every unit increase in BMI was associated with a 0.098 millimeter (mm) thinner cortex and in obese people with a 0.207 mm thinner cortex. Having a thinner cortex has been tied to an increased risk of Alzheimer’s disease.
Having a bigger waist was also associated with a thinner cortex after adjusting for other factors.
Rundek said, “In normal aging adults, the overall thinning rate of the cortical mantle is between 0.01 and 0.10 mm per decade, and our results would indicate that being overweight or obese may accelerate aging in the brain by at least a decade.”
“These results are exciting because they raise the possibility that by losing weight, people may be able to stave off aging of their brains and potentially the memory and thinking problems that can come along with brain aging,” Rundek said. “However, with the rising number of people globally who are overweight or obese and the difficulty many experience with losing weight, obviously this is a concern for public health in the future as these people age.”
Rundek noted that the study does not prove that extra weight causes the cortex to get thinner; it only shows an association.
A limitation of the study was that, like many studies of older people, it is possible that the healthiest people are more likely to live longer and take part in studies, so that may affect the results.
Funding: The study was supported by the National Institute of Neurological Disorders and Stroke and the Evelyn F. McKnight Brain Institute.
About this neuroscience research article
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Measures of obesity are associated with MRI markers of brain aging: The Northern Manhattan Study
Objective To examine associations between measures of obesity in middle to early-old age with later-life MRI markers of brain aging.
Methods We analyzed data from the Northern Manhattan MRI Sub-Study (n = 1,289). Our exposures of interest were body mass index (BMI), waist circumference (WC), waist-to-hip ratio, and plasma adiponectin levels. Our outcomes of interest were total cerebral volume (TCV), cortical thickness, white matter hyperintensity volume (WMHV), and subclinical brain infarcts (SBI). Using multivariable linear and logistic regression models adjusted for sociodemographics, health behaviors, and vascular risk factors, we estimated β coefficients (or odds ratios) and 95% confidence intervals (CIs) and tested interactions with age, sex, and race/ethnicity.
Results On average at baseline, participants were aged 64 years and had 10 years of education; 60% were women and 66% were Caribbean Hispanic. The mean (SD) time lag between baseline and MRI was 6 (3) years. Greater BMI and WC were significantly associated with thinner cortices (BMI β [95% CI] −0.089 [−0.153, −0.025], WC β [95% CI] −0.103 [−0.169, −0.037]) in fully adjusted models. Similarly, compared to those with BMI <25, obese participants (BMI ≥30) exhibited smaller cortical thickness (β [95% CI] −0.207 [−0.374, −0.041]). These associations were particularly evident for those aged <65 years. Similar but weaker associations were observed for TCV. Most associations with WMHV and SBI did not reach statistical significance.
Conclusions Adiposity in early-old age is related to reduced global gray matter later in life in this diverse sample. Future studies are warranted to elucidate causal relationships and explore region-specific associations.