Women who were obese at midlife were 79 percent less likely to be healthy at age 70 compared with women who were lean in their 40s and 50s. Even worse were those women who were obese at age 18 and then gained more than 22 pounds by middle age; their odds were reduced by 82 percent. The results were calculated by examining data from American women who participated in the Nurses' Health Study. Researchers from Harvard and the University of Warwick in England looked at the 17,065 nurses who made it to age 70 and compared the weight trends of the 9.9 percent who were considered 'healthy' with those of the rest of the group. What did it mean to be healthy? There's no standard definition, but in this study the researchers gave the designation to women who did not suffer from any of 11 major health problems, including diabetes, lung disease, heart failure and cancer (except melanoma). They also had to be in good mental health and be free of major limitations in physical or cognitive function. The healthiest nurses were those who had a body mass index between 18.5 and 22.9 at age 18 and didn't gain weight over the next 30 or so years. For every one-unit increase in BMI (about 5 or 6 pounds for a person of healthy weight), the odds of being healthy at age 70 fell by 12 percent, according to the study. In addition, women who maintained a stable weight -- regardless of initial BMI -- fared better than women who accumulated pounds over the years. For every 2.2 pounds gained, the odds of being healthy at age 70 fell by 5 percent, the researchers found. Though BMIs as high as 25 are considered healthy, the researchers found that women who had BMIs of 23 to 24.9 at midlife were 15 percent less likely to reach age 70 in prime condition compared with their leaner counterparts. The researchers focused on BMI at midlife because weight gain (or loss) after age 50 is often a consequence of a chronic disease, and they wanted to zero in on the influence of weight on health, not the reverse. Smoking could help women maintain lower BMIs, though the habit is hardly healthy. To account for this, the researchers reran the numbers with nonsmokers only and found it 'did not materially change our findings.' The depressing conclusion: Even a 'moderate weight gain' on the order of nine to 22 pounds over 30 years reduces the odds of being healthy at age 70. 'These data emphasized the significance of maintaining a healthy weight throughout adulthood to enjoy a long and healthy life,' the researchers wrote. 