The 1,503 participants included in analyses had a mean age of 59 years, were 49% male, and were predominately non-Hispanic white (42%) followed by non-Hispanic black (27%), Hispanic (20%), and non-Hispanic Chinese (11%). Over 78% of the sample was working full-time (mean number of hours spent at the workplace: 40.4 hours during the winter and 38.3 hours during the summer) (). The mean distance between the home and workplace address was 6.0 miles (standard deviation [SD]=7.0), but this varied from a mean of 3.6 miles in NY to 7.0 miles in CA and NC. Only 4.7% had a home and workplace within the same census tract, but one-mile buffers around the home and the workplace overlapped in 29.8% of participants (range: 12% in CA to 42% in NY).
Selected characteristics of participants included in the analyses for the full sample and by categories (quartiles) of the distance between home and workplace (miles), Multi-Ethnic Study of Atherosclerosis (MESA) (n=1503)
Persons travelling farther distances to work were more likely than those travelling shorter distances to be male (60% and 46% for highest vs. lowest distance quartile), non-Hispanic white (38% and 50%), and have higher household income ($71,905 vs. $62,363) and education (14.8 years vs. 14.2 years). Among those working farther from home, over 86% were working full time compared to 77% of those travelling the least distance.
Home and workplace neighborhoods differed in neighborhood features (). Home environments had greater population density and more favorable aesthetic quality, safety, and social cohesion compared to work environments (all P ≤ 0.005). However, workplace environments had more favorable SES, greater density of recreational facilities and healthy food stores, as well as more favorable walking environment, and healthy food availability compared to home environments (all P ≤ 0.0003). Despite these differences, home and work environments for participants were substantially correlated for each type of neighborhood exposure (ranging from 0.39 to 0.70).
Comparison of neighborhood characteristics of home and workplaces
For most of the neighborhood features, the difference between the home and work environment became greater as the distance increased (). Neighborhood SES was similar for locations close together, but the workplace had higher SES at greater distances (P = 0.01). At greater distances, densities of recreational facilities and healthy food stores were lower around the home than around the work (P < 0.0001) yet population density became more similar (P < 0.0001). In general, persons who travelled further for work both lived and worked in areas with lower population densities than those who travelled less for work.
Comparison of neighborhood characteristics of home and workplaces by quartiles of distance between home and work addresses
Aesthetic quality, safety, and social cohesion were similar for home and work environments located close to each other but differences increased as the distance between locations increased (P < 0.0001 for all), with home environments showing more favorable aesthetic quality, safety and cohesion, than workplace environments as the distance between them increased. There was little difference for walking environments between home and work locations and no clear pattern by distance (P = 0.79). Survey reported healthy food availability was similar when home and work were closer but became less similar at greater distances; work environments had more favorable healthy food availability (P = 0.02).
In general, point estimates of associations revealed that higher neighborhood SES, recreational facilities, safety, social cohesion, walkability, and healthy food availability were associated with lower BMI for both the home and workplace environments, although associations were not statistically significant for the workplace neighborhood SES or for home environment safety and social cohesion (, Model 1). In the case of neighborhood SES, the home environment had a much stronger association with lower BMI than the workplace environment (P for difference in coefficients = 0.047). The magnitude of the coefficients for density of healthy food stores, safety, social cohesion, and healthy food availability were higher for the workplace environment, although differences were not statistically significant. The density of recreational facilities had a stronger association for the home environment (P for difference in coefficients = 0.052). Associations of the walking environment with BMI were of similar magnitude for both environments. Associations became weaker but patterns were approximately similar when both environments were included in the same model (Model 2).
Mean differences in BMI associated with the characteristics of the home environment, the work environment and a weighted average of home and workplace environments. All models are adjusted for gender, age, race/ethnicity, income, and education.
Interactions between home and work environments were not statistically significant at P < 0.05 level except for survey reported healthy food availability. The negative interaction term suggested a synergistic effect of greater healthy food availability at both locations on lower BMI (Model 3). Weighted estimates for neighborhood SES, recreational facilities, and walking environment suggested synergy between home and workplace although uncertainty was higher (P < 0.1). In general, the magnitude of estimates using weighted averages of the home and workplace environments fell between the home and workplace estimates; the exception was walking environment for which the weighted measure had a stronger association than the separate measures for home and work (Model 4). This would suggest a synergistic effect between the home and workplace consistent with the negative interaction term (Model 3), although the latter was not statistically significant.