Effect of Smoking Cessation and Other Lifestyle Modifications on Weight Gain and Risk of Stroke: An Application of the Parametric G-Formula

Abstract

Developing public health policies for chronic disease prevention requires estimating the effects of long-term lifestyle interventions. In the absence of randomized trials conducted over long periods of time, the parametric g-formula can be used to estimate the risk of an outcome in a study population under hypothetical lifestyle “interventions” using observational data, under the assumptions of no model misspecification and no unmeasured confounding. In this dissertation, we apply the parametric g-formula to data from large prospective cohort studies to investigate the long-term effects of smoking cessation and other lifestyle modifications on weight gain and risk of stroke. In Chapter 1, we provide an estimate of long-term post-cessation weight gain in the Framingham Heart Study and show that smoking cessation can result in increased weight even after 20 years. Though the benefits of smoking cessation outweigh the health risks, post-cessation weight gain is a barrier for quitting smoking and major cause of smoking relapse, especially in women. Our results highlight the need for long-term weight management interventions in combination with smoking cessation. In Chapter 2, we estimate the reduction in post-cessation weight gain under hypothetical strategies of exercise and diet, over 10 years, in participants of the Nurses’ Health Study and Nurses’ Health Study II. We find that weight gain is detectable in women after 10 years of smoking cessation, however, by exercising for at least 30 minutes per day at a moderate-to-vigorous level and applying dietary modifications such as increasing intake of fruit and vegetables and decreasing intake of processed red meat, women may be able to considerably reduce this post-cessation weight gain. In Chapter 3, we use data from the Nurses’ Health Study to estimate the 26-year risk of stroke under hypothetical lifestyle strategies. We find that, in this population of middle-aged women, sustained lifestyle modifications such as smoking cessation, exercise, and body mass index (BMI) reduction, and dietary strategies such as increased intake of fish and nuts, and reduced intake of processed red meat were estimated to reduce the 26-year risk of total stroke by 25%, ischemic stroke by 35%, and hemorrhagic stroke by up to 26%.