The Puzzling Link Between Dementia and Weight
> 8/21/2007 2:06:05 PM

Dementia is one of the most frightening problems of old age. Even if it is not possible to prevent a slide into confusion, a forewarning before cognition fades significantly could grant valuable time for preperation. To this end,  researchers are fervently trying to find some way of predicting who will suffer neural degeneration.

Two years ago, Kaiser Permanente opened up a complicated line of investigation by singling out weight as a risk factor for dementia. They carried out a 27 year study that revealed that overweight people had a 35% greater risk for dementia and obese people a 74% greater chance. The study refers to extra weight as a risk for, as opposed to a sign of dementia. This risk was entirely separate from cardiovascular problems. One interesting quirk to note for later is that women had a much greater risk correlation than men when BMI was used, but that this sex gap closed when skin fold thickness was used instead.

More recently, Dr. David Knopman set out to find further evidence of the risk of obesity. What he found was exactly the oppositeŚweight loss seemed to predict dementia. Women in the control group who did not develop dementia gained an average of two pounds over the 30 years of the study while women who did develop dementia lost an average of 12. This weight loss began 20 years before signs of dementia and could give doctors and families significant time to prepare for life changes. Men did not show this effect, which suggests that either Knopman encountered a measuring problem similar to the one overcome by Kaiser Permanente, or that fat really does act differently in male and female bodies.

Dr. Knopman, though puzzled by his finding, offered three possible explanations: behavioral changes reduce food intake, a chemical change takes place in the body that affects weight retention, or the senses are dulled so that eating is less enjoyable.

People destined for dementia may suffer mental changes too small to show up on formal cognitive tests but large enough to alter eating habits. The earliest stages of dementia might interfere with the rhythm of daily life enough to cause sufferers to forget meals.

Dr. Knopman suggests that there could be post-menopausal hormonal changes that relate to both weight and dementia. These changes could affect anything from perceived hunger levels to the metabolic speed at which fat is broken down.

The last suggestion of Knopman's, that dementia may first dull the senses, has some concrete evidence to back it up. Last month, Dr. Robert Wilson published an intriguing study of 589 retirement home residents in the Archives of General Psychiatry. These residents were given 12 items and scored on how accurately they could identify them by smell. Those who scored in the bottom quartile were 50% more likely to develop Mild Cognitive Impairment (a form of dementia that often precedes Alzheimer's) than those who scored in the top quartile. This could very well be the explanation for Dr. Knopman's results.

Information from the Sense of Smell Institute can help make sense of Knopman's puzzle. SSI reports that 56% of those who lose their sense of smell also experience a loss of appetite. Tellingly, women are more likely to experience this loss. While we cannot make any definite conclusions, it seems likely that weight change is only a secondary indicator of dementia actually caused by a change in the the sense of smell. The Kaiser Permanente study might turn out to have the same explanation if olfactory change can cause overeating as well as appetite loss.

As weight change can have many causes, and may not even be the best indicator of dementia, it should not be seen as a clear warning sign. If you begin having difficulty detecting odors, however, it would be prudent to notify your doctor.

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