If you're middle-aged¹ 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 diabetes² might help explain the link. But it's also possible that substances produced by fat cells, such as the hormone³ 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 obesity⁴. A BMI of 25 or more indicates overweight, and 30 or more is obese⁵.

The study also investigated the relationships between BMI and cognitive⁶ 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.