Overweight girls who lose weight before they reach adulthood greatly reduced their risk for developing type 2 diabetes, according to researchers from the National Institutes of Health and Harvard University, who analyzed 16 years of data on nearly 110,000 women.

Type 2 diabetes is the most common form of the disease. It is marked by high blood sugar levels and difficulties in the body's production or use of insulin. Being overweight, exercising infrequently and having a family history of diabetes are known to contribute to the risk of developing the disease.

The findings were published online in Diabetes Care and will appear in the June issue.

The study was conducted by researchers at the Eunice Kennedy Shriver National Institute of Child Health and Human Development (NICHD). Along with the NICHD, two other NIH institutes, the National Cancer Institute and the National Institute of Diabetes and Digestive and Kidney Diseases provided funding for the analysis.

The study followed 109,172 female nurses from 1989 to 2005, noting how many developed diabetes during that time. An initial survey collected information about the women's health, history and lifestyle habits. One question asked them to pick which of a series of diagrams best matched their body shape at ages five, 10 and 20. The series of nine line drawings depicted female silhouettes of different sizes, ranging from gaunt (size 1) to obese (size 9). The nurses were also asked to provide their height and current weight and to estimate their weight when they were 18. Every two years after the initial survey, the women submitted follow-up information including whether they developed diabetes.

The researchers recorded a total of 3,307 cases of type 2 diabetes over the course of the study and found that the nurses who were overweight as girls were more likely to become diabetic as adults. Women who indicated that their size at age five matched or exceeded the size six figure were more than twice as likely to develop diabetes as those who recalled matching the size 2 figure. The women indicating the size 6 or above at age 10 were 2.57 times as likely to develop diabetes as adults. Those who reported a body mass index of more than 30 (considered obese) at age 18 were almost nine times more likely to develop diabetes than their normal-weight counterparts (BMI of 18-19).

BMI, or body mass index, is a standard measure of a person's build based on their height and weight. A BMI between 18 and 24 reflects a healthy weight.

In the study, the researchers also examined the combined effect of extra weight at various ages. Compared with women who were not overweight at key ages in childhood, adolescence and adulthood, those who indicated they were overweight at all three ages were 15 times more likely to develop diabetes. Conversely, women who recalled being overweight at age 10 but not overweight as adults were no more likely to become diabetic than their peers who had been normal-weight children.

"These findings suggest that ensuring that overweight kids reverse their weight gain is critical to limiting their future risk of diabetes as adults," said study author Edwina Yeung, of the NICHD Division of Epidemiology, Statistics and Prevention Research.

When the women entered the study, they averaged 34 years old. At that time, they were asked to recall their weight at age 18. The researchers found that women who gained weight after age 18 also increased their diabetes risk. Those who gained more than 25 pounds increased their diabetes risk more than 20 times. On the other hand, women who recalled being overweight or obese at age 18 and subsequently lost 10 pounds or more decreased their risk by more than half, compared with overweight or obese women who maintained that weight as an adult.