Visceral fat gain may have a negative impact on cerebellar structure and functional connectivity, an exploratory study suggests.
The association was apparent in young-to-middle-aged people, but not in those aged 65 years or older, say the researchers, led by Matthias Raschpichler (University of Leipzig, Germany).
"To our knowledge, this is the first study that links cerebellar dynamics with abdominal fat distribution," they write in BMJ Open.
The research also highlights the limitations of the body mass index (BMI). In contrast to visceral adipose tissue (VAT), BMI was not related to brain structure (gray matter density). And although it was associated with functional connectivity (eigenvector centrality), the interaction with age was not apparent.
"It is likely that with a cohort of participants who are overweight and slightly obese, processes related to alterations of VAT might interact below a threshold necessary for the BMI to detect changes," say Raschpichler et al.
The study involved two groups of volunteers: one of 51 people aged 20-45 years, with an average BMI of 24.9, and one of 49 people aged 65-70 years, with an average BMI of 27.0.
In the younger group only, gray matter density in both hemispheres of the cerebellum decreased as the amount of VAT, measured on magnetic resonance imaging, increased. The effect was most marked in lobule V and VI, which are thought to be involved in sensorimotor tasks, among other things.
This fits with findings of increased synaptogenesis and neurogenesis in some cerebellar areas in response to exercise training, say the researchers. "One may assume that a lack of physical activity contributes to both visceral adiposity and cerebellar brain changes."
Larger amounts of VAT were also associated with reduced cerebellar functional connectivity in the younger group, and areas in which this was most striking again included lobule VI.
Besides, sensorimotor tasks lobule VI is also involved with language, executive functions, and emotional processing. "Our findings thereby underscore an interdependency of physical activity, abdominal fat, cognitive function and cerebellar brain changes," say Raschpichler et al.
The younger group also had negative associations between VAT with connectivity in parts of the left posterior temporal and parietal lobe. None of these correlations were present in the older group, which instead showed reduced connectivity in regions governing primary motor functions as VAT increased.
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