1. State your health outcome of interest. (It could be the one you used for week #2 or another one.) Pick two key behaviors that are important factors leading to your health outcome. Explain the importance of these behaviors either for etiology, prevention, or intervention. (If none of the behaviors in the readings are important for your health outcome, suggest another behavior that is.)
The main healthy outcome of interest is pulmonary function in patients with sarcoidosis. This health outcome can be assessed in several ways, including direct physiologic measures (lung volumes, airflow, and total ability of the lungs to take up oxygen, i.e. diffusing capacity), extent of involvement on chest imaging, and symptoms of respiratory compromise. The outcomes that are most often used are physiologic measures of pulmonary function (forced vital capacity, forced expired volume in one second, total lung capacity, and diffusing capacity). Pulmonary function is affected by the extent of inflammation in the lungs due to the disease as well as the sequelae of prior inflammation in the form of fibrosis. Other factors affect these pulmonary function measures, including smoking and obesity. Smoking can cause obstructive defects on pulmonary function tests (PFTs) and can also cause reductions in diffusing capacity. It also increases symptoms of dyspnea and fatigue, which can make it difficult to assess the extent to which sarcoidosis is affecting patient’s lung function. Smoking has a negative effect on pulmonary function independent of sarcoidosis, but its role in the disease (risk of developing the disease and severity of outcomes) is complicated since prior studies have shown that patients with sarcoidosis have a lower likelihood of being smokers compared to controls. It is unclear if this has a biologic explanation (e.g. direct effect of nicotine on inflammatory cells) or is due to other reasons such as associations with other exposures. Factors that lead to obesity, such as lack of exercise and high caloric intake, can also affect pulmonary function since it can cause restrictions in the form of reduced lung volumes and can also increase shortness of breath severity. It is difficult to “adjust” for obesity when measuring pulmonary function because they PFT measures are reported as % predicted based on height and not weight. Obesity is often a sequela of the immunosuppression (prednisone) often used to treat the disease. Patients with dyspnea and fatigue from the inflammation in the disease also are less likely to exercise, which makes obesity harder to control.
2. Describe how you would study the role of one of the behaviors described for question #1 and your health outcome of interest. Incorporate a social factor (e.g. race/ethnicity, social exclusion, stress) in the study approach.
The challenge of studying the effect of smoking on pulmonary function outcomes in sarcoidosis is that once patients have the diagnosis, they are strongly encouraged to stop smoking given its known deleterious effects on pulmonary function and symptoms as well as the myriad of other negative effects it has on overall health. Therefore, studying the effect of smoking on pulmonary function outcomes in sarcoidosis would be unethical in a randomized controlled trial and observational trials would be heavily biased given that few subjects would likely continue to smoke during the trial. One could argue assessing if nicotine ingested in other ways would be worth studying given the negative association between the incidence of sarcoidosis and smoking, but the other health risks of nicotine addiction are more severe than its likely benefit. The most practical way to study the effect of smoking in sarcoidosis would be to assess prior history of smoking in observational studies as assess how it affects subsequent trajectories in PFT measurements. A dose response could be included that quantifies pack-years as well as if patients are actively smoking after they are diagnosed. It would be important to measure a social factor such as stress as a patient-reported outcome given that associations between smoking and sarcoidosis outcomes could be confounded by how well patients are able to cope with managing the disease, which is affected by stress. It would also be important to assess subjects’ occupation given that certain occupations are potentially associated with sarcoidosis and the likelihood of smoking.
3. If key health behaviors (e.g. smoking, exercise, nutritious diet) are strongly influenced by neighborhood, income, and/or education, do we need to continue to study how these behaviors influence health outcomes? Why or why not?
Smoking is influenced by income and education, which would also affect sarcoidosis patients’ outcomes. Patient’s income affects their ability to obtain and adhere to specific immunosuppressive therapies that are used to treat the disease. Income also affects where patients live, and different neighborhoods have different levels of exposure to pollution, which can affect lung function directly and patients’ symptoms. Education level affects patients’ health literacy, which also affects how well they are able to adhere to complicated immunosuppressive regimens, especially when they have negative side effect. It is therefore important to measure these behaviors so as to properly assess the main contributors to outcomes in sarcoidosis.