Even if you don’t need to watch your weight, you still need to watch your waist.

That’s the conclusion of a new study from the American Cancer Society, which tracked the health of more than 100,000 people over nine years. Having a large waist size doubled the risk of dying from any cause during the study period compared to those with smaller waists, according to the report, which was published in The Archives of Internal Medicine. Having a larger waist was associated with a higher risk of death whether the person was normal weight, overweight or obese.

The researchers reported a particularly striking finding for women. They noted that the association between waist size and mortality risk was strongest among women who were at a normal weight.

“The take-home is that it’s important to watch your waist as well as your weight,” said Eric J. Jacobs, an epidemiologist with the American Cancer Society in Atlanta. “Even if your weight is normal for your height, if your waist size is increasing, if you’re moving to a bigger pant size, that’s a warning sign that it’s time to start eating better and exercising more.”

A thick waist has long been considered a risk factor for heart disease, but the new study found it also increases risk for dying from cancer, respiratory failure and other causes. Having a large waist is associated with large amounts of visceral fat around the abdominal organs, which can cause inflammation, high cholesterol, insulin resistance and other problems linked with poor health.

In the study, Dr. Jacobs and colleagues tracked 48,500 men and 56,343 women over 50 from 1997 to 2006. A total of 9,315 men and 5,332 women died during the study period.

A waist size of 47 inches or larger for men and 42 inches or larger for women doubled the risk of dying during the study period, compared to those with smaller waists (35.4 inches for men and 29.5 inches for women). Among normal-weight women, the risk of dying increased about 25 percent for each additional four inches of waist size.

For the study, waist size was measured by taking a tape measure and running it around the waist just above the navel.

Dr. Jacobs notes that while it can be difficult to reduce waist size, small changes can have a meaningful effect on health. “There is clear evidence that eating better and exercising more will reduce waist size and burn off belly fat,” he said. “Even a modest reduction in waist size, an inch or two, could be quite helpful.”