Obesity is known to increase a person's risk of death and now, new findings from a study of more than 90,000 women indicate that the risk continues to increase as the severity of obesity worsens.

"It's not good enough to consider obesity alone," principal investigator Dr. Kathleen McTigue of the University of Pittsburgh, Pennsylvania, told Reuters Health. "You need to look at degree of obesity."

In a study published in the Journal of the American Medical Association, McTigue and colleagues evaluated the impact of body weight on death risk in 90,185 women enrolled in the Women's Health Initiative Observational Study. On average, the patients were followed for 7 years.

Body mass index (BMI), a measure of body weight for height, was used to classify the women as normal weight, overweight, or obese. Normal weight was defined as a BMI from 18.5 to 24.9 and overweight was a BMI from 25 to 29.9. The investigators defined three categories of obesity: obesity 1 (BMI of 30 to 34.9), obesity 2 (BMI 35 to 39.9) and extreme obesity (BMI 40 and higher).

"The risks of extreme obesity have not been well-defined," McTigue noted. But this study had enough subjects to assess that risk, she added.

As weight increases, so does the risk of death, but the risk is not statistically significant until one becomes obese, McTigue said. Compared with normal-weight women, she continued, "the risk of dying was increased 12 percent in all women in obesity category 1, while risk was increased 86 percent over seven years in women in obesity category 3."

In a University of Pittsburgh release, the researcher pointed out that "earlier studies, which tended to reflect lower degrees of obesity, may underestimate the risks of extremely obese individuals and overestimate the risk for mildly obese individuals in diverse groups."

She concluded, "More accurately assessing weight-related health risk may both improve policy decisions about obesity and assist women in making informed decisions about their health."