Correspondence

Adiposity and Physical Activity as Predictors of Mortality

N Engl J Med 2005; 352:1381-1384March 31, 2005

Article

To the Editor:

Hu et al. (Dec. 23 issue)1 show that both increased adiposity and reduced physical activity are strong and independent predictors of death from all causes in the Nurses' Health Study. We observed very similar findings among both men and women in the Cancer Prevention Study II, a prospective cohort study of the American Cancer Society.2 We followed 230,298 women and 90,162 men who were healthy and had never smoked when they were enrolled, in 1982. The subjects' weight, height, and level of physical activity were self-reported at enrollment. Although our measure of physical activity was crude in comparison with that used by Hu et al., our findings are quite similar (Table 1Table 1Relative Risk of Death from All Causes among Women and Men in the Cancer Prevention Study II, 1982 to 2002, According to Joint Categories of Body-Mass Index and Physical Activity.). Among both men and women, mortality rates increased independently across levels of adiposity and physical activity; among subjects who were obese and reported no physical activity, mortality rates were approximately double those among normal-weight subjects who reported heavy physical activity. It is abundantly clear that public health recommendations must focus on the benefits of both a healthy weight and regular physical activity.

Eugenia E. Calle, Ph.D.
Lauren R. Teras, M.P.H.
Michael J. Thun, M.D., M.P.H.
American Cancer Society, Atlanta, GA 30329
jcalle@cancer.org

2 References

1. 1

   Hu FB, Willett WC, Li T, Stampfer MJ, Colditz GA, Manson JE. Adiposity as compared with physical activity in predicting mortality among women. N Engl J Med 2004;351:2694-2703
   Full Text | Web of Science | Medline

2. 2

   Calle EE, Thun MJ, Petrelli JM, Rodriguez C, Heath CW. Body-mass index and mortality in a prospective cohort of U.S. adults. N Engl J Med 1999;341:1097-1105
   Full Text | Web of Science | Medline

To the Editor:

On the basis of their analysis of data from the Nurses' Health Study, Hu and colleagues conclude that obesity and physical inactivity independently predict mortality. The results, however, are not adjusted for socioeconomic status, despite its known associations with obesity, physical inactivity, and increased mortality among women.1-3 The authors maintain that “the relative homogeneity of the cohort with respect to socioeconomic status and educational level reduces confounding.”

To examine the socioeconomic homogeneity of nurses, we performed an analysis in which all white women with the same birth years as those in the cohort were selected from the 5 percent microdata sample of the 1980 U.S. Census,4 the census closest to the cohort's baseline year. Women with an occupation code (current or most recent) for “registered nurse” were compared with other white women. Family income was as heterogeneous for nurses as it was for the entire population of women (Table 1Table 1Socioeconomic Characteristics of White Women 34 to 59 Years of Age from the 5 Percent Microdata Sample of the 1980 Census.). Nurses' incomes were themselves heterogeneous and accounted for the minority of their families' incomes. Therefore, it is not clear whether the magnitude and independence of the effects of obesity and physical inactivity before and after adjustment for socioeconomic status would be similar.

Diane S. Lauderdale, Ph.D.
University of Chicago, Chicago, IL 60637
lauderdale@uchicago.edu

4 References

1. 1

   Sorlie PD, Backlund E, Keller JB. US mortality by economic, demographic, and social characteristics: the National Longitudinal Mortality Study. Am J Public Health 1995;85:949-956
   CrossRef | Web of Science | Medline

2. 2

   Crespo CJ, Smit E, Andersen RE, Carter-Pokras O, Ainsworth BE. Race/ethnicity, social class and their relation to physical inactivity during leisure time: results from the Third National Health and Nutrition Examination Survey, 1988-1994. Am J Prev Med 2000;18:46-53
   CrossRef | Web of Science | Medline

3. 3

   Sobal J, Stunkard AJ. Socioeconomic status and obesity: a review of the literature. Psychol Bull 1989;105:260-275
   CrossRef | Web of Science | Medline

4. 4

   Ruggles S, Sobek M, Alexander T, et al. Integrated public use microdata series, version 3.0. Minneapolis: Minnesota Population Center, 2003 (database).
   

Author/Editor Response

We appreciate the efforts of Calle et al. to replicate our analyses by examining data from the Cancer Prevention Study II. We are gratified to know that their results are consistent with ours in supporting the independent effects of obesity and physical activity in predicting mortality.

We also appreciate Dr. Lauderdale's comments on the potential confounding effects of socioeconomic status on our results. The census data confirm a high degree of homogeneity for educational attainment among registered nurses; 84 percent had at least some college-level education. Also, the median family income among registered nurses was higher than among women in the general population, so that even though the interquartile range and standard deviation of family income were similar to those of the general population, few participants in the Nurses' Health Study would be living in poverty. To address explicitly a potential confounding effect of household income, we further adjusted for the median annual household income (less than $27,600, $27,600 to $36,699, $36,700 to $48,599, and $48,600 or more) from the census track data based on participants' home addresses. Although a higher income was associated with a significantly lower risk of death (relative risk, 0.90; 95 percent confidence interval, 0.84 to 0.97) when the highest category was compared with the lowest, this adjustment had virtually no effect on our results. As compared with women who were lean (i.e., those with a body-mass index of less than 25) and active (i.e., they spent 3.5 or more hours per week exercising), the multivariate relative risk of death was 1.56 (95 percent confidence interval, 1.42 to 1.71) among lean but inactive women, 1.90 (95 percent confidence interval, 1.58 to 2.28) among women who were obese (i.e., those with a body-mass index of 30 or higher) but active, and 2.41 (95 percent confidence interval, 2.13 to 2.72) among inactive, obese women. Further adjustment for the occupations of the participants' parents when they were 16 years old, as well as for the educational attainment of the participants' husbands, did not materially alter our findings. These additional analyses strongly indicate that the independent effects of physical activity and obesity on mortality observed in our study are unlikely to be explained by socioeconomic status.

Frank B. Hu, M.D., Ph.D.
Walter C. Willett, M.D., Dr.P.H.
Harvard School of Public Health, Boston, MA 02115
frank.hu@channing.harvard.edu

JoAnn E. Manson, M.D., Dr.P.H.
Brigham and Women's Hospital, Boston, MA 02115

Citing Articles (8)

Citing Articles

1. 1

   Suan Peng Ng, Rosemary Korda, Mark Clements, Isabel Latz, Adrian Bauman, Hilary Bambrick, Bette Liu, Kris Rogers, Nicol Herbert, Emily Banks. (2011) Validity of self-reported height and weight and derived body mass index in middle-aged and elderly individuals in Australia. Australian and New Zealand Journal of Public Healthno-no
   CrossRef

2. 2

   Leanne M. Redman, Eric Ravussin. (2011) Caloric Restriction in Humans: Impact on Physiological, Psychological, and Behavioral Outcomes. Antioxidants & Redox Signaling 14:2, 275-287
   CrossRef

3. 3

   D. S. Lauderdale, K. L. Knutson, P. J. Rathouz, L. L. Yan, S. B. Hulley, K. Liu. (2009) Cross-sectional and Longitudinal Associations Between Objectively Measured Sleep Duration and Body Mass Index: The CARDIA Sleep Study. American Journal of Epidemiology 170:7, 805-813
   CrossRef

4. 4

   Harpreet S. Bajaj, Danielle M. Brennan, Byron J. Hoogwerf, Krupa B. Doshi, Sangeeta R. Kashyap. (2009) Clinical Utility of Waist Circumference in Predicting All-cause Mortality in a Preventive Cardiology Clinic Population: A PreCIS Database Study. Obesity 17:8, 1615-1620
   CrossRef

5. 5

   Leanne M. Redman, Eric Ravussin. (2009) Endocrine alterations in response to calorie restriction in humans. Molecular and Cellular Endocrinology 299:1, 129-136
   CrossRef

6. 6

   Alpa V. Patel, Heather Spencer Feigelson, Jeffrey T. Talbot, Marjorie L. McCullough, Carmen Rodriguez, Roshni C. Patel, Michael J. Thun, Eugenia E. Calle. (2008) The role of body weight in the relationship between physical activity and endometrial cancer: Results from a large cohort of US women. International Journal of Cancer 123:8, 1877-1882
   CrossRef

7. 7

   Lars J. Vatten, Tom I.L. Nilsen, P??l R. Romundstad, Wenche B. Dr??yvold, Jostein Holmen. (2006) Adiposity and physical activity as predictors of cardiovascular mortality. European Journal of Cardiovascular Prevention & Rehabilitation 13:6, 909-915
   CrossRef

8. 8

   Leanne M Redman. (2006) Physical activity and its effects on reproduction. Reproductive BioMedicine Online 12:5, 579-586
   CrossRef