July 20, 2010
Men and women with Alzheimer’s disease often lose muscle mass, and the loss of muscle may be linked to shrinkage of the brain. The findings, which appeared in the Archives of Neurology, a medical journal from the American Medical Association, highlight the fact that Alzheimer’s disease is not just a disease of the brain but of the body as well.
Alzheimer’s is a progressive illness that shuts down the body as it attacks the mind. But while most people think of Alzheimer’s as a disease that affects memory and thinking skills, the physical toll of Alzheimer’s is often overlooked. In the current study, the authors found that loss of lean muscle mass – the weight of a person’s muscles, bones and internal organs, rather than body fat – was linked to an increased likelihood of Alzheimer’s disease.
Earlier studies have shown that seniors who quickly shed pounds are at higher risk of developing Alzheimer’s, and mental decline may be particularly rapid in such cases. Dementia may be especially likely in those who were overweight to begin with and then lose weight. Weight loss may precede the onset of Alzheimer’s by 10 to 20 years in some cases, suggesting that the disease may have a long latency period during which subtle changes like weight loss or minor memory problems may occur.
Paradoxically, those who are obese or who have other risk factors for heart disease during midlife may be at increased risk for Alzheimer’s during their late years. “Although obesity in midlife is a risk factor for developing dementia, overweight and obesity in late life are associated with lower dementia risk,” wrote the authors, from the University Of Kansas School Of Medicine in Kansas City.
In the current study, the researchers used a type of body scan called dual-energy x-ray absorptiometry, or DEXA, to assess body composition in 140 men and women age 60 and older. Half had early-stage Alzheimer’s and the others were mentally intact. Study participants were also given MRI brain scans as well as tests to measure memory and mental function
Taking into account differences in muscle mass between men and women, the investigators found that those with Alzheimer’s had less lean mass than their healthy peers. Those with Alzheimer’s also had smaller brains and less brain white matter, suggesting their brains had begun to atrophy, or waste away. Percentages of total body fat, however, were not different between the two groups.
The findings suggest that lean mass is a better measure of whether Alzheimer’s is present than more popular measures of body fat, like the body mass index, or BMI.
“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,” the authors wrote. Wasting of the brain, as demonstrated by brain scans, correlated with wasting of the muscles.
Typically, men and women lose muscle mass with age. Declining muscle mass is strongly linked to diminished physical activity. Indeed, in the current study, seniors with Alzheimer’s were less active than those without the disease.
The authors speculate that changes in the brain may disrupt the nervous system’s ability to regulate energy or maintain healthy food intake. Alternatively, Alzheimer’s disease and loss of muscle may share an underlying mechanism, such as inflammation or changes in the process of building tissue.
Jeffrey M. Burns, MD, MS; David K. Johnson, PhD; Amber Watts, PhD; et al: “Reduced Lean Mass in Early Alzheimer Disease and Its Association With Brain Atrophy.” Archives of Neurology, Vol. 67(No. 4): April 12, 2010.