The Relationship between Overweight in Adolescence and Premature Death in Women
Context Do overweight female adolescents have a higher risk for premature death during adulthood? Contribution The authors of this prospective cohort study recruited 102400 U.S. female nurses, 24 to 44 years of age, asked about their weight at age 18 years, and then monitored deaths that occurred within 12 years after recruitment. Compared with a reported body mass index (BMI) of 18.5 to 21.9 kg/m2, the hazard ratio for death was 1.18 for a BMI of 22.0 to 24.9 kg/m2, 1.66 for a BMI of 25.0 to 29.9 kg/m2, and 2.79 for a BMI of 30 kg/m2 or greater. Implications Adiposity at age 18 years is associated with increased mortality rates in younger and middle aged women. The Editors The prevalence of overweight and obesity is increasing in the United States and worldwide in children and adults (13) Being overweight during childhood and adolescence can have detrimental consequences on psychological and social factors, cardiovascular risk factors, and risk for chronic diseases and is associated with a higher prevalence of obesity in adulthood (4) Several studies have examined whether adiposity in childhood and adolescence is also related to premature death in adulthood (515) However, these studies largely concerned older birth cohorts that included few participants who were overweight during youth and few who never smoked (6, 810, 1214) In addition, data from more recent studies are needed to address the proposition that the impact of obesity on death may have decreased recently because of advances in public health and medical care (16) Whether weight management in adulthood can prevent detrimental effects of childhood adiposity on adult health is relevant for prioritization of preventive efforts. Few studies have examined whether associations between childhood adiposity and adult death are merely due to tracking of adiposity between childhood and adulthood or whether independent effects of childhood adiposity exist (9, 17) Other issues that require study include the degree of adiposity that is associated with elevated rates of premature mortality and the shape of this association. U shaped associations between body mass index (BMI) in middle age and death have been reported, and whether the higher mortality rates for the leanest persons represent a biological effect or a methodologic artifact remains controversial (16, 18) Weight loss due to health conditions that precede death can bias associations between BMI and death in middle aged and older populations (19, 20) Such a reverse causation bias (19) is less likely to affect associations for adolescent adiposity because the prevalence of chronic disease is very low at this age. Data on the association between adolescent adiposity and premature death can provide insight into the importance of preventing excessive weight gain during childhood and adolescence. We therefore examined BMI at age 18 years in relation to death during 12 years of follow up (1989 to 2001) in a large cohort of younger and middle aged U.S. women. Methods Study Population We used data from the prospective Nurses' Health Study II. This cohort included 116671 female U.S. nurses who were 24 to 44 years of age at study initiation in 1989. Information has been collected using biennial mailed questionnaires, and response rates have been approximately 90% for each follow up questionnaire. The response rate to the baseline mailing was 24% Our strategy was to use a single baseline mailing to enroll only the most enthusiastic potential participants who would complete a questionnaire after 1 request, allowing us to achieve high response rates for follow up questionnaires. We excluded participants with a history of cancer (except nonmelanoma skin cancer) (0.9% pregnancy at study initiation (4.3% or missing information for any of the variables used in the analyses (7.0% of the remaining women) A total of 102400 women remained for the current analysis. Mean age (34.4 years [SD, 4.7] vs. 34.5 years [SD, 4.7] ethnicity (non Hispanic white, 90.3% vs. 90.0% and BMI at age 18 years (available for 99.0% of the total study population; 21.3 kg/m2 [SD, 3.4] vs. 21.3 kg/m2 [SD, 3.4] were very similar for the total study population and the sample that remained for the current analysis, respectively. The human research committees at Harvard School of Public Health and Brigham and Women's Hospital approved the study. Ascertainment of Death Deaths were reported by next of kin or by postal authorities (85.3% or were ascertained through searching the National Death Index for nonresponders (14.7% For the original Nurses' Health Study, the follow up for deaths using the National Death Index has been estimated to be 98% complete (21) Given the young age of the cohort, we considered all deaths to be premature. Information on the cause of death was obtained from next of kin for external deaths (such as those due to traffic accidents) death certificates; or medical records. We requested permission from the next of kin to review medical records for suspected deaths from cancer or cardiovascular diseases if we had not yet obtained these records for follow up of disease incidence. The cause of death was determined after physician review and was primarily based on medical records if both medical records and death certificates were available. Collection of information on causes of death is an ongoing process, and coding of causes of death was 82% complete at the current analysis. International Classification of Diseases, Eighth Revision (ICD 8) codes were used to assign the underlying cause of death as cancer (codes 140 through 207) cardiovascular diseases (codes 390 through 459 and 795) all other diseases, and external causes (codes E800 through E999) including suicide (codes E950 through E959) Assessment of BMI and Body Circumference Measures On the 1989 baseline questionnaire, participants were asked to report current weight (in pounds) and height (in inches) and weight at age 18 years (in pounds) Body mass index was calculated as weight in kilograms divided by the square of height in meters. Among 118 participants, recalled weight at age 18 years and self reported current height were compared with records from physical examinations conducted at college or nursing school entrance (22) The Spearman correlation was 0.87 for recalled and measured past weight, 0.94 for self reported current height and measured past height, and 0.84 for BMI at age 18 years based on self reports and measurements. The average reported weight was 1.4 kg lower than the measured weight, the average reported height was 0.6 cm higher than the measured past height, and the average BMI at age 18 years based on self reports was 0.5 kg/m2 lower than that based on measurements. Age in 1989 was not appreciably associated with the degree of underestimation of weight (r 0.01) or height (r 0.02) at age 18 years. The validation study did not include enough women who were overweight at age 18 years to allow comparison of accuracy of self reports for women who were and who were not overweight at age 18 years. Reported current weight was validated among 140 participants from the original Nurses' Health Study. The correlation between self reported and technician measured weight was 0.97; 99% were correctly classified within 1 quintile, and the average self reported weight was 1.5 kg lower than the measured weight (23) In 1993, we mailed a paper tape measure and pictorial instructions to participants to obtain self measured waist circumference at the umbilicus and the largest hip circumference between the waist and the thighs and compared these assessments with technician measurements in a validation study (r= 0.89 for waist circumference and r= 0.84 for hip circumference) (23) Assessment of Adolescent and Adult Lifestyles and Medical History On the baseline questionnaire administered in 1989, we requested information about age, disease history, cigarette smoking habits at different ages and at present, usual frequency of consuming alcoholic beverages at different ages and during the past year, history of oral contraceptive use (24) history of hormone replacement therapy, average amount of participation in vigorous physical activities from age 18 to 22 years (number of months per year for at least twice per week) and current recreational and work related physical activities (25) Statistical Analysis We grouped women into 5 categories of BMI at age 18 years by using the World Health Organization (WHO) categories (26) and an additional cutoff point within the normal weight category. Women contributed follow up time from the date of return of the baseline questionnaire to the date of death or 1 July 2001, whichever came first. Mortality rates for categories of BMI were expressed as the number of deaths per 100000 person years, and 95% CIs for rates were calculated on the logarithmic scale assuming an approximately normal distribution. Rate differences were calculated by subtracting rates, and 95% CIs for rate differences were calculated assuming an approximately normal distribution. Cox proportional hazards regression models stratified by 5 year age categories and 2 year calendar time periods were used to calculate hazard rate ratios for the association between BMI and premature death. The multivariate model with adjustment for adolescent covariates included cigarette smoking at age 15 to 19 years (0, 1 to 14, and 15 cigarettes per day) strenuous physical activity at age 18 to 22 years (none, 1 to 3 months per year, 4 to 6 months per year, 7 to 9 months per year, and 10 to 12 months per year) consumption of alcoholic beverages at age 18 to 22 years (0, 1 drink per week to 1 drink per month, 2 to 6 drinks per week, and 1 drink per day) and use of oral contraceptives at age 18 years (ever or never) The model with additional adjustment for adult covariates also included smoking status (0, 1 to 14, 15 to 24, and 25 cigarettes per day) physica
Annals of Internal Medicine