Baseline characteristics are presented in . By design, the sample was 50% female and 50% African American. Mean age of the study sample was 75.3 years. There was a total of 147 deaths within 3 years of enrollment. Intentional weight loss was reported by 8.8% of participants, and unintentional weight loss was reported by 19.1%. Two percent of the sample was underweight, 29.3% were normal weight, 37.7% were overweight, 20.3% were obese class I, and 10.5% were obese class II or III. Baseline characteristics differed significantly by BMI category.
In both the raw and adjusted Cox proportional hazards models (), older age, male gender, recent smokers, greater comorbidities, intentional weight loss, and Underweight BMI category significantly predicted mortality. In the adjusted model, underweight participants were more than 2 times as likely to experience mortality within 3 years compared with participants in the Normal Weight BMI category. There was no association between being overweight, obese, or grossly obese and mortality. In the adjusted model, older adults reporting unintentional weight loss were 1.67 times more likely to experience mortality than those who reported no weight loss. There was no difference in mortality between participants who reported intentional weight loss and those who reported no weight loss. There was also no association between race and 3-year mortality.
Cox Proportional Hazards Models
An additional proportional hazards model was conducted that included a BMI Group × Weight Loss Group interaction effect. This interaction effect was not statistically significant (χ2 (7) = 1.04, p = .99). Combining this with the multivariable findings in , it was evident that both the Underweight BMI effect and the unintentional weight loss effect were independent of each other, and that the effect of unintentional weight loss on mortality did not differ as a function of BMI group.
Our findings indicate that older adults who were either underweight or experienced unintentional weight loss had a higher risk of mortality compared with those who were normal weight, overweight, or obese and who did not experience unintentional weight loss. Additionally, older adults who were either obese or grossly obese had the lowest risk of mortality compared to all other groups. Our findings are consistent with those of other studies that found a reverse j-shaped relationship with BMI and mortality (19
Our study has implications for public health in several regards. First, despite increasing rates of obesity occurring among all age groups in society, a significant proportion of the older population continues to experience undernutrition (22
). There are many causes of undernutrition that may be amenable to conservative treatment. Second, although not statistically significant, the nature of the relationship between intentional weight loss and mortality suggests that there might have been a beneficial effect. These findings are consistent with the findings of Gregg and colleagues (24
), who included only overweight and obese adults in their study.
This is an observational study limited by the difficulty inherent in relying on a self-report measure to distinguish between intentional and unintentional weight loss (25
). Our study is also limited in that it was of only 3 years duration, the exact amount of weight lost is not known, and the weight loss question was asked only with regard to the previous year. An additional limitation of this study is that we do not have measures of the distribution of body fat and, specifically, intra-abdominal fat, which some researchers have indicated may be more important than BMI in predicting mortality (26
). This study, as well as others, indicates the need for randomized clinical trials that carefully evaluate the effect of weight reduction, caloric intake, and physical activity on morbidity and mortality in community-dwelling older adults.