Children and adolescents in the U.S. and around the world are becoming more overweight. A new study from the Harvard School of Public Health (HSPH) has found that there may be serious consequences to that trend. Researchers found that being overweight at age 18 is associated with an increased risk of premature death in younger and middle-aged women. The study appears in the July 18, 2006 issue of the Annals of Internal Medicine.
"Our findings add to studies on overweight in middle-aged and older populations by providing insight into the impact of adolescent overweight on adult mortality," said Rob van Dam, a research scientist in the Department of Nutrition at HSPH and lead author of the study.
Some previous studies had looked at the relationship between being overweight in childhood and adolescence and premature death in adulthood, but those studies tended to look at older cohorts (people born before 1945), in which few participants were overweight during their youth and the majority had smoked.
Van Dam and his colleagues examined data from 102,400 female nurses in the Nurses' Health Study II, a prospective study launched in 1989. At that time, study participants, all aged 24 to 44, reported their current height and weight and their weight at age 18. Researchers calculated body mass index (BMI)--weight in kilograms divided by the square of height in meters. Participants also answered questions in a number of other areas, including disease history, alcohol consumption, smoking and exercise. Follow-up questionnaires were sent to participants until July 1, 2001, or to the date of death, whichever came first.
The results showed that women with a higher BMI at 18 consumed more alcohol, smoked more and were less likely to engage in vigorous physical activity during adolescence.
During the 12-year follow-up period (1989-2001), in which 710 participants died, the HSPH researchers found that women with a higher BMI at age 18 had a higher risk of dying prematurely. That was true for even moderately overweight adolescents. Associations between overweight and premature mortality were similar for women who were younger and older than 40 during follow-up. Major causes of death included cancer (258 deaths) and cardiovascular disease (55 deaths); of the deaths due to external causes (144 deaths), suicide was the most common cause (61 deaths).
The researchers also found that women with a low BMI at age 18 did not have an increased risk of mortality. This finding contrasts with several recent studies, in which both a low and high BMI in middle-aged and older adults was associated with excess mortality. However, at older ages, a low BMI may reflect lifelong smoking habits or weight loss as a result of diseases, which may bias associations between BMI and mortality.
To adjust for smoking, van Dam and his colleagues looked at the results for women who never smoked. They found the same results--women with a higher BMI during adolescence who never smoked had a significantly increased risk of premature death than those with a low BMI. Another key finding was that BMI at age 18 was a strong predictor of BMI in 1989 when women were, on average, 34 years old. Still, BMI in 1989 only partly explained the association between BMI at age 18 and premature death. In other words, being overweight as an adult couldn't fully explain why women died prematurely. Health effects of overweight that are specific to younger ages, differences in location of fat deposition, or long-term exposure to metabolic effects of overweight may explain this finding.
Past studies have also shown that overweight children and adolescents have higher risks of cardiovascular problems and chronic diseases. The results of this study, which show a risk of premature death for younger and middle-aged women, are in line with these findings. "This paper underscores the importance of efforts to prevent excessive weight gain in children, not only to prevent obesity but also to prevent moderate overweight," said Frank Hu, associate professor of nutrition and epidemiology at HSPH and a co-author of the study. "Given the prevalence of overweight, large-scale preventive strategies aimed at increasing physical activity and stimulating healthy eating habits in U.S. children and adolescents are warranted."
This study was supported by a grant from the National Institutes of Health.
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