Using data from Hispanic respondents from five well-characterized cohort studies of adults aged >18 years who were followed for an average of nearly 13 years, we found that overweight and obesity were not associated with increased mortality rate. The results from the HEPESE, a cohort study that enrolled adults aged ≥65 years at baseline, showed that overweight and obesity were associated with decreased mortality rate. Other investigators33–37
have found similar findings within older populations. In contrast, underweight was associated with increased mortality rate for all attained-age categories for the PRHHP and SAHS data sets, and for the 18 – <60 years attained-age group for NHANES III (although it should be noted that underweight respondents in SAHS and NHANES comprised <5% and 1% of the total sample size, respectively).
The association between underweight and increased mortality rate is consistent with previous BMI-mortality rate studies.38,39
Although we accounted for smoking in the models, we did not omit those who died early in follow-up to address the notion of ‘occult disease’ (i.e., undetectable diseases that might associate with both weight loss and mortality). Cancer-related weight loss tends to occur well after diagnosis,41,42
whereas other diseases (e.g., Alzheimer’s disease, Parkinson’s infections) can produce weight loss before their diagnosis. However, a number of methodological papers39,40
have shown that dropping those who die early in follow-up and/or those with recent weight loss from the analysis does not account for the elevated BMI-mortality rate association observed among the underweight.
Although seemingly paradoxical, our results are also consistent with the findings of numerous studies,43–48
which show a Hispanic-mortality-rate advantage despite the populations’ lower socioeconomic status and increased risk of health conditions such as asthma, diabetes and metabolic syndrome. The reasons for this so-called ‘Hispanic paradox’ are unknown, but do not appear to be satisfactorily explained by methodological factors such as racial and ethnic misclassification on death certificates, or migration and cultural effects pertaining to diet, lifestyle, family structure and social networks.1,44,45–51
Though highly speculative, it is also possible that culturally-driven differences in body image and body attitude52–54
may compel fewer Hispanic adults to attempt weight loss, which raises the possibility that the absence of repeated bouts of weight loss and regain (i.e., weight cycling) may contribute to a reduction in the association of BMI to mortality rate observed in this population. Although not all Hispanic subgroups have experienced similar social integration to mainstream society, the impact of acculturation, resilience and social support continue to be important areas for further study.
Strengths of this study include the use of five well-characterized data sets containing a relatively large number of Hispanic respondents, a consistent analytic approach, use of attained age and stratification to account for confounding and for effect modification by age, and the generation of weighted estimates that combine the HRs derived from the five data sets.
This study has certain limitations. First, the data sets we used were limited primarily to Mexican Americans and Puerto Rican respondents. As the Hispanic population varies markedly on variables such as socioeconomic status, and demographic and lifestyle characteristics, such as age structure, fertility, diet, and social and family networks,43–51
our results may not be representative of the Hispanic population as a whole. A related issue concerns the fact that data from the PRHHP were collected during a considerably different time period (1965–1980) than the other data sets. This introduces heterogeneity that is not accounted for in the statistical models (however, omitting the estimates derived from the PRHHP does not substantially alter the estimates). Moreover, age was available only in 4-year categories in PRHHP, which caused interval censoring of our end points in these data. We are not aware of any methods designed for handling interval censoring in Cox models stratified according to the attained age with left truncation. We acknowledge that our approach to handling this imprecision may have yielded underestimated standard errors of parameter estimates. However, we do not believe that this biased the parameter estimates. Finally, it is important to note that, consistent with most obesity-mortality studies, we generated our HRs based on the National Heart, Lung and Blood Institute (NHLBI) BMI-defined obesity categories. Although this allows for direct comparisons with estimates derived from other cohorts24,25,29
, it raises the possibility that we may have obtained substantially different HRs if we had chosen other BMI-defined categories, particularly a different reference category. However, as a sensitivity analysis, we generated additional sets of HRs using the BMI-defined reference category of 23 – <25 kg m−2
(data not shown). On the whole, the HRs generated were consistent with those derived with the NHLBI reference category of 18.5 – <25. The exceptions were the larger HRs in the 18.5 – <23 kg m−2
category obtained in the 60 – <70 years attained-age category in NHANES III and the HEPESE, as well as in the combined estimates for the 18 – <60 years and 60 – <70 years attained-age categories. These results are not surprising as they likely reflect the slight elevation in risk on the left end of the U-shaped curve typically seen in BMI-mortality analyses. There were also two slightly elevated HRs in the 25 – <30 range (i.e., for HEPESE and combined estimates for the 60 – <70 years attained-age category, 1.32 and 1.17, respectively). Similarly, this likely reflects a lowering of the mortality rate in the reference category by removing individuals in the 18.5 – <23 range, individuals who tend to display an elevated mortality risk. However, given the modest magnitude of the HRs, the issue of multiple testing, confidence intervals that were wider than those obtained from the NHLBI-defined reference category, and the lack of a clear dose–response relationship between BMI >25 kg m−2
and MR, the results of the sensitivity analysis confirm that there is no clear evidence that overweight and obesity associate with elevated mortality rate among Hispanic adults.
In total, we offer BMI-mortality rate estimates that are restricted only to Hispanic respondents. Overweight and obesity do not appear to associate with elevated mortality rate among Hispanic adults. Our findings have significant public health implications as we continue to examine the pathogenic role of excess body weight in diverse populations. Although Hispanics have higher rates of obesity and diabetes, the life expectancy for Hispanics is 2.5 years longer than the life expectancy for non-Hispanic Whites and almost 8 years longer than non-Hispanic Blacks.1
Moreover, on average, Hispanics have lower median family incomes, higher poverty rate and are less likely to have a college education compared with non-Hispanic Whites; yet these are characteristics associated with better health and longer life.46–51
Thus, our findings support the need for more research to better understand the predictors of healthy long life, and how clinicians might use the results from well-characterized studies to counsel patients of diverse background about healthy weight and its relationship to chronic disease prevention, healthy life and health care expenditure.