This study was undertaken to test whether the effect of dietary meat on mortality differed according to levels of neighborhood socioeconomic status, using a large prospective study of older U.S. adults. The primary question of interest was whether the type and quantity of meat consumption had a more deleterious effect in poorer neighborhoods than more affluent areas based on a census-tract socioeconomic deprivation index. We found that the risk of mortality from consumption of red and processed meats did not differ across neighborhoods of varying levels of socioeconomic deprivation. With regards to white meat intake, results suggest potential socioeconomic inequalities in total cancer mortality in men (largest effects being observed in the least deprived census tracts), whereas in women these inequalities were not as apparent.
Our findings of sex differences between deprivation and mortality are in accord with previous studies that found the socioeconomic-mortality association is weaker in women than men for person-level indicators of SES (31
). The risks of mortality for men and women with high meat intakes are consistent in both magnitude and significance (e.g., linear trends) with those previously reported by Sinha and colleagues (6
The mechanism by which neighborhood deprivation influences the protective effect of white meat consumption, but not that of red or processed meats, is not clear. The observed benefits may partly be explained by differences in the physical environment or social norms. In particular, men residing in areas with higher deprivation may have issues such as limited availability of or access to healthy foods and health care, and lack of social networks that might impact mortality risk independently of the characteristics of the people living in those areas (20
). There might also be differences in the preparation or type of white meat consumed (e.g., more fried chicken, less fish) for those living in more socioeconomically disadvantaged neighborhoods. Eating white meat may be correlated with other health-promoting behaviors that were not measured or inadequately adjusted particularly among men.
Among the inherent strengths of the present study is the prospective design in which neighborhood deprivation and covariates were measured prior to mortality, which unlike ecologic study designs, permits examination of causation and provides data at both the individual- and aggregate-level. In addition, the NIH-AARP Study consisted of participants from 6 states and 2 metropolitan areas and was not limited to a specific geographical location as with other U.S. prospective studies examining area-based effects on mortality. Extensive data collection of information on lifestyle and medical history allowed us to control for possible confounding on a broad array of characteristics and lifestyle factors. In addition, we employed an innovative analytic method, the extended Cox model with a robust variance estimator, to simultaneously examine associations of person-level and area-level risk factors with mortality, which is unique in research examining the influence of neighborhood on mortality. Further, the large size of the NIH-AARP Diet and Health Study allowed us to stratify the study population by gender and examine interactions while maintaining study power.
A limitation of our study is that the cohort was predominantly upper-to-middle class Caucasians; therefore, results may not apply to more diverse populations. However, our study was population-based and more broadly generalizable to the general U.S. population than prospective studies examining meat intake and mortality in specific geographic locations or specific study populations (34
). Even within the NIH-AARP Diet and Health Study population that may have a limited range of neighborhood deprivation scores, we were still able to observe an effect modification by deprivation on the association between white meat intake and mortality. It is possible that this effect might actually be stronger for a population that has more diversity in socioeconomic status. Alternatively, it is possible that differences across categories of neighborhood deprivation reflect incomplete adjustment for person-level factors, including household income and occupation. In addition, data on the social norms, physical environment, quality of foods and the availability or access to healthy foods and health care was not ascertained; therefore, it was not possible to directly assess inequalities on these measures. To our knowledge, other prospective studies have not yet examined effect modification of these four mentioned factors on the association between meat intake and mortality and that the present study is the first to examine the impact of neighborhood deprivation on the associations. Although this information was not ascertained in the present study, the analyses were adjusted for a wide range of characteristics and lifestyle factors indicative of cancer and cardiovascular disease, including an extensive in-depth measure of smoking history and dietary intake. As it was not feasible to obtain clinical measures from a cohort of this magnitude, BMI was based on self-reported body weight and height. Self-reported and actual weight has been reported to be strongly correlated among U.S. adults (36
). While residual confounding of BMI may exist, the consistency of our results for BMI with those of other studies would suggest that the influence of this type of bias was likely weak. Because we investigated multiple endpoints, it is possible that significant results may be due to chance. Future studies are needed to replicate these findings and to examine direct measures of neighborhood deprivation.
In conclusion, red and processed meat intake increases mortality risk regardless of the level of deprivation within a given neighborhood, even after accounting for a large number of known risk factors for mortality. Findings suggest biological mechanisms rather than neighborhood contextual factors may underlie these particular meat-mortality associations. Possible socioeconomic inequalities may exist among men with regards to white meat intake and risk of cancer mortality. Our findings require confirmation in other U.S. populations, including younger age groups and populations with a wider range of SES. If confirmed, the information gained could potentially be useful in identifying inequalities in lifestyle as well as the geographical areas most likely to benefit from strategies aimed at promoting a healthy environment.