A Co-Twin control study of fine particulate matter and the prevalence of metabolic syndrome risk factors

The relationship between ambient fine particulate matter (PM2.5) and metabolic syndrome (MetS) is under-studied. It also remains unknown whether familial factors play a role in this relationship. In a study of 566 middle-aged twins, we examined the association of PM2.5 with MetS risk factors, measured by a MetS score as a summation of individual risk factors (range, 0 to 5). High-resolution PM2.5 estimates were obtained through previously validated models that incorporated monitor and satellite derived data. We estimated two-year average PM2.5 concentrations based on the ZIP code of each twin's residence. We used ordinal response models adapted for twin studies. When treating twins as individuals, the odds ratio of having 1-point higher MetS score was 1.78 for each 10 mu g/m(3)-increase in exposure to PM2.5 (confidence interval [CI]: 1.01, 3.15), after adjusting for potential confounders. This association was mainly between pairs; the odds ratio was 1.97 (CI: 1.01, 3.84) for each 10 mu g/m(3)-increase in the average pairwise exposure level. We found no significant difference in MetS scores within pairs who were discordant for PM2.5 exposure. In conclusion, higher PM2.5 in residence area is associated with more MetS risk factors. This association, however, is confounded by shared familial factors.