Effect of weight on depression using multiple genetic instruments.

A striking global health development over the past few decades has been the increasing prevalence of overweight and obesity. At the same time, depression has become increasingly common in almost all high-income countries. We investigated whether body weight, measured by body mass index (BMI), has a causal effect on depression symptoms in Finland. Using data drawn from the Cardiovascular Risk in Young Finns Study (N = 1,523, mean age 41.9, SD 5), we used linear regression to establish the relationship between BMI and depression symptoms measured by 21-item Beck's Depression Inventory. To identify causal relationships, we used the Mendelian randomization (MR) method with weighted sums of genetic markers (single nucleotide polymorphisms, SNPs) as instruments for BMI. We employ instruments (polygenic risk scores, PGSs) with varying number of SNPs that are associated with BMI to evaluate the sensitivity of our results to instrument strength. Based on linear regressions, higher BMI was associated with a higher prevalence of depression symptoms among females (b = 0.238, p = 0.000) and males (b = 0.117, p = 0.019). However, the MR results imply that the positive link applies only to females (b = 0.302, p = 0.007) but not to males (b = -0.070, p = 0.520). Poor instrument strength may explain why many previous studies that have utilized genetic instruments have been unable to identify a statistically significant link between BMI and depression-related traits. Although the number of genetic markers in the instrument had only a minor effect on the point estimates, the standard errors were much smaller when more powerful instruments were employed.

Mothers as insurance: Family spillovers in WIC.

The Special Supplemental Nutrition Program for Women, Infants, and Children (WIC) is a widely used program. Previous research shows that WIC improves birth outcomes, but evidence about impacts on older children and their families is limited. We use a regression discontinuity leveraging a loss of benefits at age five when children become ineligible for WIC and examine nutritional and laboratory outcomes for adults and children. We find little impact on children who aged out of the program. But caloric intake falls and food insecurity increases among adult women, suggesting that mothers protect children by consuming less themselves. We find no effect on others in the household.

Rebates as incentives: The effects of a gym membership reimbursement program.

A rich experimental literature demonstrates positive effects of pay-per-visit fitness incentives. However, most insurance plans that provide fitness incentives follow a different structure, offering membership reimbursements conditional on meeting a specific attendance threshold. We provide the first evidence in the literature on gym incentives of this structure, exploiting the introduction and subsequent discontinuation of a large-scale wellness program at a major American university. Our analysis leverages individual-level administrative data on gym attendance for the universe of students over a five-year period: the three years that the policy was in place, one year before implementation, and one year after termination. This provides us with 100,000 student-year observations and 1.5 million gym visits. Using bunching methods and difference-in-difference designs, we provide four empirical results. First, we document that the policy led to significant bunching at the attendance threshold. Second, we show that the program increased average gym visits by almost five visits per semester, a 20% increase from the mean. Third, we find that the policy not only motivated students who were previously near the threshold, but rather increased attendance across the entire visit distribution. Finally, we show that approximately 50% of the effect persists a year after program termination. Taken together, these results suggest that rebate-framed incentives with a high attendance threshold can induce healthy behaviors in the short-term, and that these positive behaviors persist even after the incentives have been removed.

Unintended consequences of health insurance: Affordable Care Act's free contraception mandate and risky sex.

Health insurance is a primary driver of rising medical expenditures. Economic theory suggests that insurance induces an increase in risky behaviors, but previous empirical evidence is mixed. I use a mandate in the Affordable Care Act in which contraceptives were covered at zero cost to consumers to test for unintended effects of insurance on risky sex. Leveraging mandated zero cost-sharing for contraception and pre-policy insured rates as a measure of treatment intensity, I provide evidence that this 2012 policy reduced fertility but caused unintended consequences: a decline in condom use and a subsequent increase in sexually transmitted infections (STIs). I discuss shortcomings of controlling for nonparallel pre-trends using state-trends, and I suggest an alternative to control for pre-trends directly in the context of dose-response difference-in-differences. Finally, estimates based on the 2010 dependent coverage mandate indicate health insurance provides an overall net positive effect on insurance and STI prevention.

The effect of weight on mental health: New evidence using genetic IVs.

Average body mass index (BMI) and depression prevalence grew over the last several decades, increasing medical expenditures. There is a strong correlation between obesity and depression but limited evidence on the causal effect of weight on mental health. I use an index of genetic risk for high BMI as a source of exogenous variation in weight to provide novel evidence on the effect of weight on mental health. This is one of the first studies to use genetics as an instrument for BMI and to examine the causal relationship between weight and depression. Results are mixed; I find a meaningful and significant effect of weight on suicidal ideation but no effects on counseling and an index of depression. The effect on suicidal ideation is concentrated in white females. From respondent and interviewer opinions of respondent attractiveness, social stigma is a mechanism through which weight affects mental health for white women.