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Center for Human Nutrition
Department of International Health
Bloomberg School of Public Health
Johns Hopkins University
615 North Wolfe Street
Baltimore, MD 21205
Department of Epidemiology and Nutrition
Harvard School of Public Health
Cambridge, MA
E-mail: ywang{at}jhsph.edu
Dear Sir:
We thank Heinz et al for their interest in our study (1). We share their view that gain in waist circumference (WC) is an important predictor of type 2 diabetes. In a recent study in the Health Professionals Follow-Up Study cohort, we found that WC gain during adulthood was positively associated with an increased risk of type 2 diabetes, independent of weight change in middle-aged and elderly men. Compared with men with a stable waist circumference, those whose WC increased by >14.6 cm had a 70% (odds ratio: 1.7; 95% CI: 1.0, 2.8) increase in diabetes risk after baseline WC was controlled for (2). In the same model, baseline WC was also a significant predictor, which suggests that both baseline WC and subsequent WC gain are important risk factors for developing type 2 diabetes, although which is a better predictor has yet to be thoroughly evaluated. Because we did not have WC measurements for the participants at age 21 y, it is not possible for us to examine the relation between WC gain since age 21 y and subsequent risk of type 2 diabetes in this cohort.
Heinz et al suggested an interesting approach to predict WC. Their data show that a prediction model including age, height, and weight can explain 82% of the variance in WC. Using the most recent National Health and Nutrition Examination Survey data collected in 2001-2002 from American adults aged 18 y, we confirmed the usefulness of the model in predicting WC (R2 = 0.91 in US men and 0.85 in US women). The good predictivity of the model, however, is primarily driven by a very strong correlation between WC and BMI or body weight (Table 1).
View this table:
TABLE 1. Correlations between waist circumference and age, height, weight, and BMI in US men and women1
On the basis of the model, a measure of weight change would provide almost the same information as a measure of WC change because height remains largely constant over time for the same individual. This is not unexpected because weight gain in middle-aged and elderly people is primarily due to gain in fat tissue. In men younger than 60 y, weight gain is almost entirely a change in fat tissue, predominantly around the waist. In our previous analysis (2), both weight and WC gains during adulthood were strongly associated with increased diabetes risk. We estimated that 56% of the cases of diabetes in this cohort could be attributed to a weight gain >7 kg, and 20% of the cases could be attributed to a waist gain >2.5 cm, although we were only able to measure the participants' WC change from middle age onward, not from age 21 y. These findings underscore the critical importance of maintaining weight and waist to reduce the risk of diabetes.
In clinical settings, body weight—not WC—is routinely measured because it is easier to measure and interpret. Ideally, clinicians should measure both weight and WC and keep track of changes in both variables for their patients, although, for most people, a clinically significant weight gain is usually accompanied by expanding waistlines and vice versa.
ACKNOWLEDGMENTS
None of the authors had a conflict of interest.
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