‘Skinny fat’ is a predictor of cognitive impairment risk

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CognitionA US study has found that “skinny fat” – the combination of low muscle mass and strength in the context of high fat mass – may be an important predictor of cognitive performance in older adults. While sarcopenia, the loss of muscle tissue that is part of the natural ageing process, as well as obesity both negatively impact overall health and cognitive function, their coexistence poses an even higher threat, surpassing their individual effects.

The study was led by researchers at Florida Atlantic University’s Comprehensive Centre for Brain Health in the Charles E Schmidt College of Medicine.

Using data from a series of community-based aging and memory studies of 353 participants, the researchers assessed the relationship of sarcopenic obesity or skinny fat with performance on various cognition tests. The average age of the participants was 69. Data included a clinic visit, valid cognitive testing such as the Montreal Cognitive Assessment and animal naming; functional testing such as grip strength and chair stands; and body composition (muscle mass, body mass index, percent of body fat) measurements.

Results from the study show that sarcopenic obesity or “skinny fat” was associated with the lowest performance on global cognition, followed by sarcopenia alone and then obesity alone. Obesity and sarcopenia were associated with lower executive function such as working memory, mental flexibility, self-control and orientation when assessed independently and even more so when they occurred together.

Using a cross-sectional design, the researchers found consistent evidence to link sarcopenic obesity to poor global cognitive performance in the study subjects. This effect is best captured by its sarcopenic component with obesity likely having an additive effect. This effect extends to specific cognitive skills, in particular executive function.

“Sarcopenia has been linked to global cognitive impairment and dysfunction in specific cognitive skills including memory, speed, and executive functions,” said senior author Dr James E Galvin, one of the most prominent neuroscientists in the country, associate dean for clinical research and a professor of integrated medical science in FAU’s Schmidt College of Medicine, and a professor in FAU’s Christine E Lynn College of Nursing.

“Understanding the mechanisms through which this syndrome may affect cognition is important as it may inform efforts to prevent cognitive decline in later life by targeting at-risk groups with an imbalance between lean and fat mass. They may benefit from programs addressing loss of cognitive function by maintaining and improving strength and preventing obesity.”

Obesity may contribute to the risk of impaired executive function through vascular, behavioural, metabolic, and inflammatory mechanisms or can result from reduced impulse control, self-monitoring, and goal-directed behaviour in individuals with impaired executive function with a negative effect on the ability to maintain energy balance.

The exact mechanisms linking obesity to cognitive dysfunction are yet to be determined, although several pathways including sedentary behaviour, inflammation, and vascular damage have been proposed. Sarcopenia, in turn, has been linked to impairments in abilities that relate to conflict resolution and selective attention. Executive function is reduced in obese older adults, and improvement in muscular function has been linked to enhancement of executive function in senior adults.

Galvin and his study collaborators, Dr Magdalena I Tolea, a research assistant professor of integrated medical science, and Dr Stephanie Chrisphonte, a research assistant professor of integrated medical science, both in FAU’s Schmidt College of Medicine, caution that changes in body composition including a shift toward higher fat mass and decreased lean muscle mass represent a significant public health concern among older adults as they may lead to various negative health outcomes including cardiovascular and neurodegenerative diseases.

“Sarcopenia either alone or in the presence of obesity, can be used in clinical practice to estimate potential risk of cognitive impairment,” said Tolea. “Testing grip strength by dynamometry can be easily administered within the time constraints of a clinic visit, and body mass index is usually collected as part of annual wellness visits.”

This study was supported by grants from the National Institute on Aging of the National Institutes of Health, the Morris and Alma Schapiro Fund and the New York State Department of Health.

Abstract
Background: Sarcopenia and obesity both negatively impact health including cognitive function. Their coexistence, however, can pose an even higher threat likely surpassing their individual effects. We assessed the relationship of sarcopenic obesity with performance on global- and subdomain-specific tests of cognition.
Patients and methods: The study was a cross-sectional analysis of data from a series of community-based aging and memory studies. The sample consisted of a total of 353 participants with an average age of 69 years with a clinic visit and valid cognitive (eg, Montreal Cognitive Assessment, animal naming), functional (eg, grip strength, chair stands), and body composition (eg, muscle mass, body mass index, percent body fat) measurements.
Results: Sarcopenic obesity was associated with the lowest performance on global cognition (Est.Definition1=−2.85±1.38, p=0.039), followed by sarcopenia (Est.Definition1=−1.88±0.79, p=0.017) and obesity (Est.Definition1=−1.10±0.81, p=0.175) adjusted for sociodemographic factors. The latter, however, did not differ significantly from the comparison group consisting of older adults with neither sarcopenia nor obesity. Subdomain-specific analyses revealed executive function (Est.Definition1=−1.22±0.46 for sarcopenic obesity; Est.Definition1=−0.76±0.26 for sarcopenia; Est.Definition1=−0.52±0.27 for obesity all at p0.05) and orientation (Est.Definition1=0.59±0.26 for sarcopenic obesity; Est.Definition1=−0.36±0.15 for sarcopenia; Est.Definition1=−0.29±0.15 all but obesity significant at p<0.05) as the individual cognitive skills likely to be impacted. Potential age-specific and depression effects are discussed.
Conclusion: Sarcopenia alone and in combination with sarcopenic obesity can be used in clinical practice as indicators of probable cognitive impairment. At-risk older adults may benefit from programs addressing loss of cognitive function by maintaining/improving strength and preventing obesity.

Authors
Magdalena Tolea, Stephanie Chrisphonte, James Galvin

Florida Atlantic University material
Clinical Interventions in Ageing abstract


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