CHICAGO (AP) -- Overweight women who lost as little as five pounds handled everyday activities more easily and had fewer aches and pains, a study found.

Gaining as little as five pounds had the reverse effect in normal-weight and overweight women, the researchers reported in Wednesday's Journal of the American Medical Association.

The four-year study of more than 40,000 nurses, ages 46 to 71, is one of the few to show that small changes in weight can have a big effect on quality of life.

Most research on overweight people has focused on dire long-term risks - diabetes, high blood pressure, heart disease, stroke and cancer.

"The vast majority of overweight people don't end up getting those diseases. But when we're talking about things like being able to walk up stairs, we're talking about something that potentially affects everyone," said Dr. Ichiro Kawachi, a professor of medicine who helped lead the study at Harvard-affiliated Brigham and Women's Hospital in Boston.

A separate study in JAMA reported that obese women are more than six times as likely as lean women to have a silent inflammation in their arteries that may boost their already elevated risk of heart disease. The study involved more than 16,000 Americans. The results were first reported in April at a meeting in Washington by obesity researcher Marjolein Visser of Vrije University in Amsterdam, the Netherlands.

In the nurses' study, overweight women who shed some weight tended to function better physically and had more vitality and less pain.

Dr. Michael Steelman, past president of the American Society of Bariatric Physicians, specialists in medical issues related to weight, said modest weight loss can give people an emotional boost, too. "It gives them the kind of self-confidence they need to move ahead with their life, perhaps to earn promotions, to change jobs, to improve relationships," he said.