Early dementia causes weight loss
Women show signs of physical change a decade before mental decline.
Researchers have found a simple physical symptom that accompanies the early, subtle brain changes that lead to dementia. Women who will go on to develop dementia begin to lose weight at least ten years before diagnosis, say researchers at the Mayo Clinic in Rochester, Minnesota.
While the symptom of weight loss is too common to serve as a usable early warning sign for mental decline, researchers hope other such physical changes could be used to spot dementia before memory loss sets in.
David Knopman, who led the study published in Neurology1 today, thinks the women may have shed the weight because creeping damage in their brains caused them to lose interest in food. He speculates that the disease could cause apathy or dull the senses of taste and smell, making food less appealing.
Neurologists have long suspected that conditions such as Alzheimer's disease begin to develop 10-20 years before diagnosis. But spotting such early changes has proven difficult. This is one of only a few studies to make a link between physical symptoms and emerging dementia.
"It's an interesting development in terms of how we think about dementia," says Robert Stewart, an epidemiologist at London's Institute of Psychiatry who has previously found a hint of a link between dementia and weight loss2.
Knopman says the goal now is to understand better how the weight loss happens, and hopefully to find other, more definitive physical markers of impending mental decline that could be detected with blood tests or brain scans.
The link between approaching dementia and losing weight was made using the unusually extensive medical records held at the Mayo Clinic as part of the Rochester Epidemiology Project, set up over 40 years ago to provide accurate data for almost any serious medical condition. 295 patients diagnosed with dementia were matched by age and sex with a randomly selected unaffected person, and their weights compared over the years running up to diagnosis.
At the age of 40, both groups weighed the same. But by the time memory loss was recognised by clinicians, the dementia patients were an average of 5.4 kilograms lighter than the control group.
Knopman and his colleagues saw that the difference was attributable to the women when the data for men and women were separated. And slimming down started to occur at least a decade before the disease was spotted. In contrast to Stewart's earlier work on Japanese-American men, Knopman's team did not see weight loss in male dementia patients.
The gender difference might be social, says Knopman. In the population he studied, he says, it could be that men were more likely to have meals cooked for them, making forgetting, or not bothering, to make meals less of a problem. In his clinical work, Knopman says he has seen women with dementia regain weight when they move to assisted living facilities with supervised meals.
Knopman says it is unlikely that the weight loss seen in his study was a cause rather than an effect of mental decline. The gradual shedding of pounds as the disease progressed was so modest that it would not be expected to cause problems. And previous studies have suggested that being obese in middle age, rather than too slim, increases the risk of getting dementia.
- Knopman, D. S. et al. Neurology 69, 739-746 (2007).
- Stewart, R. et al. Arch. Neurol. 62, 55-60 (2007).