If you're middle-aged and your memory's not what it used to be, check the bathroom scale（体重秤） , researchers warned, suggesting overweight people tend to score more poorly on tests of memory than their thinner peers do. 

The findings suggest that a heavier weight in middle age may mean a higher risk of dementia later in life.

Reporting in the journal Neurology, the researchers speculated that higher rates of cardiovascular disease or diabetes might help explain the link. But it's also possible that substances produced by fat cells, such as the hormone leptin（瘦素） , have direct effects on the brain.

The study compared mental abilities to body mass index (BMI), a measurement of weight in relation to height used to define overweight and obesity. A BMI of 25 or more indicates overweight, and 30 or more is obese.

The study also investigated the relationships between BMI and cognitive function in 2,223 healthy men and women between the ages of 32 and 62 in France through the use of four cognitive tests.

The study found a higher BMI was associated with lower cognitive test scores. Results from a test involving word memory recall show people with a BMI of 20 remembered an average of nine out of 16 words, while people with a BMI of 30 remembered an average of seven out of 16 words.