Association Between Soda Consumption and Body Mass Index in the University of Washington Twin Registry

Thesis (Master's)--University of Washington, 2015-12Background: Obesity is of major public health concern due to its association with many chronic diseases and its history of increased prevalence. Obesity development is influenced by both genetic and environmental factors. This study improves upon previous studies of body mass index and soda consumption by using an informed twin design to decipher how genetic and shared environmental affect this association. Methods: Data was collected from a large cohort of same sex, adult twin pairs, ages 18-97 from the University of Washington Twin Registry. Associations among all twins were calculated using generalized estimating equations (GEE), accounting for twin relatedness, followed by within-twin pair differences associations which controlled for shared genetic and environmental factors within twin pairs. Results: All among twin analyses, including unadjusted and sequentially adjusted models, showed a positive association between BMI and soda consumption (p<.001). In the fully adjusted model, individuals drinking 1-2 sodas per day had a 1.0 kg/m2 (SE: 0.11) unit greater BMI than twins reported no soda consumption per day. Additionally, all twin differences analyses showed a positive association between BMI and soda consumption (p<.001). The fully adjusted model suggested a 1.0 kg/m2 unit greater BMI (SE: 0.069) for each unit increase in soda consumption, as categorized by the ordinal values of 1-2, 3-4, and 5+ sodas per day. The within-twin pair results were not statistically different when stratified by zygosity. Conclusion: Among a large group of adult twin pairs, increased soda consumption was associated with increased BMI, and this relationship was not confounded by genetic and shared environmental factors within twins