A test of famine-induced developmental programming in utero

Scarring In Utero: An Attempt to Validate With Data Unconfounded by Migration and Medical Care

BACKGROUND

"Scarring in utero" posits that populations exposed to injurious stressors yield birth cohorts that live shorter lives than expected from history. This argument implies a positive historical association between period life expectancy (i.e., average age at death in year t) and cohort life expectancy (i.e., average lifespan of persons born in year t). Tests of the argument have not produced consistent results and appear confounded by autocorrelation, migration, and access to medical care. Here we test whether, as predicted by scarring in utero, sex-specific period and cohort life expectancy appear positively related among Swedes born from 1751 through 1800. If scarring has ever influenced longevity, we should detect signals of its effects in these cohorts because, unlike other populations with known life span, they aged in place and unlikely benefitted from increased access to efficacious medical care.

METHODS

We use Box-Jenkins methods to control autocorrelation and measure associations.

RESULTS

Contrary to the scarring hypothesis, we find an inverse association between period and cohort life expectancy. Our findings imply that, among males, variation in injurious stress on the population predicted changes in cohort life span ranging from a gain of approximately 67 weeks to a loss of about 45 weeks of life and among females from a gain of approximately 68 weeks to a loss of about 38 weeks of life.

CONCLUSION

Epidemiologists trying to understand and explain temporal variation in cohort life expectancy should view the scarring argument with greater skepticism than currently found in the literature.

Dust to Feed, Dust to Gray: The Effect of in Utero Exposure to the Dust Bowl on Old-Age Longevity

Intensive agriculture and deep plowing caused topsoil erosion and dust storms during the 1930s, affecting agricultural income and land values for years. Given the growing literature on the relevance of in utero and early-life exposures, it is surprising that studies focusing on links between the Dust Bowl and later-life health have produced inconclusive and mixed results. We reevaluate this literature and study the long-term effects of in utero and early-life exposure to topsoil erosion caused by the 1930s Dust Bowl on old-age longevity. Specifically, using Social Security Administration death records linked with the full-count 1940 census, we conduct event studies with difference-in-differences designs to compare the longevity of individuals in high- versus low-topsoil-erosion counties before versus after 1930. We find intent-to-treat reductions in longevity of approximately 0.85 months for those born in high-erosion counties after 1930. We show that these effects are not an artifact of preexisting trends in longevity. Additional analyses suggest that the effects are more pronounced among children raised in farm households, females, and those whose mothers had lower education. We also provide suggestive evidence that reductions in adulthood income are a likely mechanism for the effects we document.

Pandemic influenza and gender imbalance: Mortality selection before births

This study uses data from the 1918-1920 influenza pandemic in Japan along with newly digitized and complete census records on births and infant deaths to analyze mortality selection in utero. I find that fetal exposure to the influenza pandemic during the first trimester of the pregnancy decreases the proportion of males at birth. The results from mechanism analysis suggest that this decline in male births is associated with the deterioration of fetal and infant health. This result supports a wide range of existing literature on the long-run adverse effects of pandemic influenza.

Reproductive suppression and longevity in human birth cohorts

OBJECTIVES

Reproductive suppression refers to, among other phenomena, the termination of pregnancies in populations exposed to signals of death among young conspecifics. Extending the logic of reproduction suppression to humans has implications for health including that populations exposed to it should exhibit relatively great longevity. No research, however, has tested this prediction.

METHODS

We apply time-series methods to vital statistics from Sweden for the years 1751 through 1800 to test if birth cohorts exposed in utero to reproductive suppression exhibited lifespan different from expected. We use the odds of death among Swedes age 1 to 9 years to gauge exposure. As the dependent variable, we use cohort life expectancy. Our methods ensure autocorrelation cannot spuriously induce associations nor reduce the efficiency of our estimates.

RESULTS

Our findings imply that reproductive suppression increased the lifespan of 24 annual birth cohorts by at least 1.3 years over the 50-year test period, and that 12 of those cohorts exhibited increases of at least 1.7 years above expected.

CONCLUSIONS

The best available data in which to search for evidence of reproductive suppression in humans support the argument that populations subjected to environments dangerous for children yield birth cohorts that exhibit unexpectedly great longevity.