The more weight a woman puts on after her teen years, the more likely she is to develop urinary incontinence in her late 30s to early 50s, a new study shows.

"Urinary incontinence is a common condition, even in these middle-aged women," Dr. Mary K. Townsend of the Channing Laboratory at Brigham and Women's Hospital in Boston, the study's lead author, told Reuters Health. "It's important that women feel comfortable speaking about incontinence with their doctor."

Most studies of urinary incontinence have been limited to older women, Townsend noted in an interview, although up to 40 percent of women under 60 may have the problem.

Many studies have linked incontinence with excess weight, but these investigations were unable to show whether gaining weight caused the problem or vice versa; for example, it might be that incontinent women chose not to exercise, and gain weight as a result, Townsend and her colleagues note in the medical journal Obstetrics & Gynecology.

To investigate the obesity-incontinence link over time in younger women, she and her colleagues looked at 30,982 women in the 37-to 54 age range participating in the Nurses' Health Study. All had reported their weight at age 18, and gave updated information on their weight every two years.

Women with a current body mass index (BMI) of 35 or above, indicating severe obesity, were more than twice as likely as women with BMIs below 23 to have developed incontinence during the course of the study, Townsend and her team found.

The more weight women gained after age 18, the greater their risk of developing urinary control problems. Women who gained from 5.1 to 10 kilograms (11.2 to 22 pounds) were 44 percent more likely to become incontinent than those who kept their weight within 2 kilograms (4.4 pounds) of what it was at age 18, while those who gained more than 30 kilograms (66 pounds) were at more than fourfold increased risk of incontinence compared to those who put on fewer than 2 kilograms.

There are a number of possible explanations for why excess weight might worsen bladder control, Townsend noted. Abdominal obesity is thought to boost pressure within the bladder, stressing the muscles responsible for controlling urination, while insulin resistance related to obesity may lead to nerve damage that impairs the brain's control over the bladder.

The good news, she added, is that women can improve their urinary control by trimming down. "Losing weight does improve incontinence... That has been shown to be an effective strategy," she said.