Despite widespread publicity of the obesity epidemic in the US and other developed countries, its prevalence remains unabated. With almost 20% of children and adolescents and 40% of adults in the US with obesity, we face a public health crisis. Blacks, Hispanics, and people with low socioeconomic status are disproportionately affected. Multi-level and multi-pronged approaches are needed to stem this epidemic. One recommended approach is population-based strategies that make it easier for people to make more healthful choices. One such strategy is imposing taxes to reduce consumption of sugar-sweetened beverages (SSB). Not only are SSB the largest contributor of added sugar in the US diet and have been tied to obesity and its comorbidities, but national survey data suggest that of adults and 2/3 of youth consume at least one SSB on a given day. If taxes can reduce SSB consumption, it follows that obesity prevalence will fall, along with obesity-related diseases. In Berkeley, CA (the first city to levy a SSB tax [in 2015]) SSB sales declined 9.6% and SSB consumption declined 19.8% in the first year after tax implementation. There are indications that effects were greater in low-income neighborhoods. We propose to evaluate the natural experiment of SSB taxes on weight change in youth and adults and to explore possible effects on glycated hemoglobin (HbA1c) levels and diabetes incidence among a cohort of adults with prediabetes. Oakland, Albany, and San Francisco have also levied an excise tax on SSB ? cities in which a large number of residents are patients (approximately 230,000 adults and 50,000 youth) of Kaiser Permanente Northern California (KPNC). Using our electronic medical records (EMR), we will examine body mass index (BMI; kg/m2) trajectories, HbA1c levels, and incidence of diabetes prior and after initiation of SSB taxes, using two different analyses (synthetic controls and differences in differences) to optimize the rigor of our results. KP patients living in Northern California and Southern California cities comparable to cities with a SSB tax will be used as controls. We hypothesize that cities with a SSB tax will experience favorable changes in BMI, HbA1c, and diabetes incidence compared with comparison cities.
Our specific aims are to 1) Examine differences in BMI trajectories and prevalence of overweight and obesity before and after implementation of a SSB tax among youth and adults separately in California cities with and without a SSB tax. 2) Assess how youth and adult characteristics, such as age, race/ethnicity, BMI category, and neighborhood socioeconomic status, may modify the impact of SSB taxes on BMI and prevalence of overweight and obesity. 3) Explore differences in mean HbA1c levels and diabetes incidence among an age/sex/race/BMI and neighborhood socioeconomic status matched cohort of adults with prediabetes who live and do not live in SSB tax cities. This information is needed to guide health advocates and policy makers with respect to the role of SSB taxes in obesity prevention.
Obesity prevalence is a public health concern that needs multiple interventions at multiple levels to conquer. One strategy is the policy of implementing excise taxes on sugar-sweetened beverages (SSBs). We will examine the effects of city-level SSB taxes on body mass index and diabetes incidence among prediabetics. This study will be the first to examine health outcomes and include control cities without similar taxes.
