WASHINGTON - Older women hoping to keep their minds young should keep an eye on the scale -- researchers have found a link between slowing down mentally and piling on the pounds/(kilos).

For every extra point gained on a scale of obesity, scores in reasoning, memory and other mental skills fell, Dr. Diana Kerwin of Northwestern University in Chicago and colleagues found.

"What we found is that actually obesity in and of itself is an independent risk factor for declining cognitive performance," Kerwin said in a telephone interview.

She used data from the Women's Health Initiative, an ongoing national study of illness and death among older American women. She compared women's body mass index, or BMI, a measure of obesity commonly used by doctors and researchers, to their results on a test that measured their mental sharpness.

The test evaluated the memory, abstract reasoning, writing, and temporal and spatial orientation skills of the group of women aged 65 to 79.

Among the 8,745 post-menopausal women who completed the test, for each point increase in the BMI scale, scores on the mental test went down by one point, Kerwin's team reported on Wednesday in the Journal of the American Geriatric Society.

"While the women's scores were still in the normal range, the added weight definitely had a detrimental effect," she said.

"Even if you do have normal blood pressure and you're not diabetic, it still should be something that's looked at as an independent risk factor for your brain health."

Kerwin is conducting other studies to see if where the fat is on the body matters -- for instance if it is around the waist or on the hips.

But for now, she says, the important finding is that for older women with obesity, "even if your blood pressure's normal, even if you're not diabetic, even if your cholesterol's normal, you should still be discussing this with your doctor."

BMI is a measure of height to weight and is calculated by dividing weight in kilograms by height in meters squared. A person 5 feet 5 inches tall becomes overweight at a BMI of 25, or 150 pounds (68 kg), and obese at 180 pounds (82 kg), which equals a BMI of 30.