Women entering their senior years with a healthy weight and waist size have a significantly better chance of reaching age 85 without chronic disease or mobility impairment, according to a nationwide health study that followed more than 36,000 women for up to 19 years.

Put another way, a 66-year-old woman with a body mass index (BMI) over 30, combined with a waist circumference of about 34 inches, has increased odds of coronary and cerebrovascular disease, diabetes mellitus, certain cancers, hip fractures and arthritis over the subsequent two decades later – if she lives that long. (BMI is a measure of body fat based on height and weight. People with a BMI of 30 or over are considered obese.)

“We’ve always thought that maintaining a healthy weight was important for health, function and longevity among aging women, but this study quantifies that relationship in a very powerful way,” says Rebecca Seguin, assistant professor of nutritional sciences. She is co-author of new findings, “Obesity and Late-Age Survival Without Major Disease or Disability in Older Women,” which was published Nov. 11 in JAMA (Journal of the American Medical Association) Internal Medicine.

Noting that the number of women 85 years and older in the United States is increasing rapidly – with 11.6 million projected by 2050 – and that previous “late-age survival” studies had often focused on men, the researchers examined data from 36,611 female participants from the Women’s Health Initiative, a long-term observational study with 40 participating clinical centers across the country.

“We looked at women’s weight because obesity is a potentially modifiable risk factor for physical disability and several chronic diseases that affect older women,” Seguin explained. “Genetic risk factors are largely out of our hands, but our body weight and waist size are things that lifestyle change can impact.”

“According to the Honolulu Heart Program/Honolulu Asia Aging Study, men who are leaner at midlife have better late-age survival and better health, but studies in women were lacking. This 2013 study helps fill that gap,” Seguin said.

The cumulative effect of those extra pounds and inches is “striking,” the research team concluded: Higher BMI and waist size is associated with a dramatically increased risk of mobility disability as well as increased risk of death and disease. The good news is the opposite is also true: Maintaining a healthy BMI and waist size increases the likelihood of surviving to older ages without major disease or disability, the researchers wrote.

They directed this message to policymakers and to aging individuals: “Successful strategies aimed at maintaining healthy body weight, minimizing abdominal fat accretion, and guiding safe, intentional weight loss for those who are already obese should be further investigated and disseminated.”

The study was funded, in part, by the National Heart, Lung and Blood Institute, an agency of the U.S. Department of Health and Human Services.