Fat Infiltration of Muscle Correlates with Age-Related Cognitive Decline
Researchers here show that great fat infiltration of skeletal muscle tissue correlates well with the progressive loss of cognitive function that occurs with advancing age. It is well demonstrated that greater visceral fat mass accelerates the declines of aging, but researchers here suggest that fat deposition in skeletal muscle correlated with cognitive decline independently of the degree to which study participants were overweight. The underlying reasons as to why two people of the same overall adiposity may have different degrees of intramuscular fat deposition are not well understood, but this manifestation of aging correlates well with many aspects of age-related dysfunction, including chronic inflammation, metabolic syndrome, and other usual suspects. In a web of correlations, it can be challenging to identify cause and effect.
Obesity and loss of muscle mass are emerging as risk factors for dementia, but the role of adiposity infiltrating skeletal muscles is less clear. Skeletal muscle adiposity increases with older age. In 1,634 adults (69-79 years), we obtained thigh intermuscular adipose tissue (IMAT) via computerized tomography at Years 1 and 6, and mini-mental state exam (3MS) at Years 1, 3, 5, 8 and 10.
A linear mixed effects models tested the hypothesis that increased IMAT (Year 1-6) would be associated with 3MS decline (Year 5-10). Models were adjusted for traditional dementia risk factors at Year 1 (3MS, education, APOe4 allele, diabetes, hypertension, and physical activity), with interactions between IMAT change by race or sex. To assess the influence of other muscle and adiposity characteristics, models accounted for change in muscle strength, muscle area, body weight, abdominal subcutaneous and visceral adiposity, and total body fat mass (all measured in Years 1 and 6). Models were also adjusted for cytokines related to adiposity: leptin, adiponectin, and interleukin-6.
Thigh IMAT increased by 4.85 cm^2 (Year 1-6) and 3MS declined by 3.20 points (Year 6-10). The association of IMAT increase with 3MS decline was statistically significant: an IMAT increase of 4.85 cm^2 corresponded to a 3MS decline of an additional 3.60 points, indicating a clinically important change. Interactions by race and sex were not significant. Clinicians should be aware that regional adiposity accumulating in the skeletal muscle may be an important, novel risk factor for cognitive decline independent of changes to muscle strength, body composition, and traditional dementia risk factors.