Economics

This paper studies how peers’ genetic predisposition to depression affects own mental health during adolescence and early adulthood using data from the National Longitudinal Study of Adolescent to Adult Health (Add Health). I exploit variation within schools and across grades in same-gender grademates' average polygenic score—a linear index of genetic variants—for major depressive disorder (the MDD score). An increase in peers' genetic risk for depression has immediate negative impacts on own mental health. A one standard deviation increase in same-gender grademates' average MDD score significantly increases the probability of being depressed by 1.9 and 3.8 percentage points for adolescent girls (a 7.2% increase) and boys (a 25% increase), respectively. The effects persist into adulthood for females, but not males. I explore several potential mechanisms underlying the effects and find that an increase in peers' genetic risk for depression in adolescence worsens friendship, increases substance use, and leads to lower socioeconomic status. These effects are stronger for females than males. Overall, the results suggest there are important social-genetic effects in the context of mental health.

Many health conditions have a strong genetic component. We examine whether genetic factors related to risky health behaviors explain variation in health. Using data from the Health and Retirement study, we estimate associations between health and the genetic endowments linked to smoking initiation and intensity. Among those aged 50-65, higher genetic predisposition for smoking is associated with worse health, even after flexibly controlling for individual smoking behavior and among those who have never smoked, suggesting the genetic endowments correlate with health through non-smoking channels. The genetic endowments for smoking correlate with longevity expectations, planning horizons, and measures of conscientiousness, but these channels do not fully explain the estimated relationship between genetic risk for smoking and health. Furthermore, we find that an increase in a spouse's genetic risk for smoking intensity has adverse spillovers for own health. Overall, our results suggest the genetic factors linked to smoking capture a complex array of traits that correlate with less engagement in health-promoting activities.

Alzheimer’s disease and related dementias (ADRD) are widespread and costly. The severe under-diagnosis of ADRD impedes many people from preparing for its health and economic consequences. Existing work has identified several genetic predictors of ADRD, including APOE-ε4 and a polygenic score for ADRD, but genes do not yet figure prominently in ADRD screening. Using data from the Health and Retirement Study, we examine whether these genetic factors can significantly improve the prediction of future ADRD beyond what is possible using standard observables like past cognitive test scores and family history. We then test whether individuals with elevated genetic risk engage in behaviors that could help them plan for or respond to future ADRD. APOE-ε4 carriers face dramatically higher rates of future ADRD, and we find weak evidence that they are aware of their elevated risk and engage in some financial and legal preparations. Individuals with higher polygenic scores are also more likely to develop ADRD, but are significantly less likely to engage in planning activities, such as having long-term care insurance or a durable power of attorney. These results raise the possibility that genetic screening can help individuals at risk of ADRD, but who are unaware and unprepared and thus especially vulnerable to such risk.