The lean mass of people with Alzheimer’s disease may fall, according to a new report in the April issue of Archives of Neurology, a JAMA/Archives journal. Lean mass is a person’s total weight, including bones, muscles and organs – but without the body fat. The study found that lean mass drop may be linked with a fall in brain volume and function.
People with Alzheimer’s disease commonly lose weight unintentionally – this frequently occurs before memory loss or other cognitive signs and symptoms become apparent, say the authors. The weight loss is linked to dementia severity and speed of progression of the Alzheimer’s disease. The authors explain “Although obesity in midlife is a risk factor for developing dementia, overweight and obesity in late life are associated with lower dementia risk.”
Jeffrey M. Burns, M.D., M.S., of the University of Kansas School of Medicine, Kansas City, and colleagues used dual-energy x-ray absorptiometry (DEXA) to assess body composition in 70 individuals aged at least 60 years without dementia and 70 with early-stage Alzheimer’s disease. Participants were also evaluated with brain magnetic resonance imaging (MRI) and neuropsychological testing.
After controlling for sex, lean mass was reduced among patients with Alzheimer’s disease compared with healthy controls. Decreases in the volume of the whole brain and of white matter only, along with declines in cognitive performance, were linked to lean mass loss. However, total body fat and body fat percentage were not different between individuals with and without dementia and were not associated with cognitive ability or brain volume.
The findings suggest that lean mass, rather than body mass index (BMI) or other measures of overall weight or fat levels, may be a more sensitive measure of the changes in body composition associated with dementia. The authors wrote “We observed a direct correlation between whole-brain volume (an estimate of brain atrophy) and lean mass, suggesting that brain atrophy and loss of muscle mass may co-occur. Brain atrophy is considered a neuroimaging measure reflective of Alzheimer’s disease pathology. Thus, our data are consistent with other studies suggesting that brain pathology may contribute to decline in body composition, perhaps by disrupting central nervous system regulation of energy metabolism and food intake.”
Sarcopenia – the degenerative loss of skeletal muscle mass and strength associated with aging – is most closely linked with reductions in physical activity, the authors note. Individuals in the study with Alzheimer’s disease had lower levels of physical activity; therefore, behavioral changes associated with dementia may contribute to the loss of lean mass, the authors note. Alternatively, Alzheimer’s disease and sarcopenia may share an underlying mechanism, such as inflammation or changes in the process of building tissue.
Source
Archives of Neurology
Written by Christian Nordqvist