Katherine Saxton

The Health Effects of Economic Decline

Political pronouncements and policy statements include much conjecture concerning the health and behavioral effects of economic decline. We both summarize empirical research concerned with those effects and suggest questions for future research priorities. We separate the studies into groups defined by questions asked, mechanisms invoked, and outcomes studied. We conclude that although much research shows that undesirable job and financial experiences increase the risk of psychological and behavioral disorder, many other suspected associations remain poorly studied or unsupported. The intuition that mortality increases when the economy declines, for example, appears wrong. We note that the research informs public health programming by identifying risk factors, such as job loss, made more frequent by economic decline. The promise that the research would identify health costs and benefits of economic policy choices, however, remains unfulfilled and will likely remain so without stronger theory and greater methodological agreement.

Economic Contraction and Mental Health

Background: Theory and empirical evidence suggest that economic contraction predicts increased incidence of psychological disorder. The extent to which this relation can be causally attributed to the economic experiences of individuals remains uncertain. Methods: We critically examine literature concerning the impact of economic contraction, measured at the individual or ecological level, on four mental health outcomes (depression, suicide, substance abuse, and antisocial behavior) from the past two decades. Studies at the individual level use job loss, transition to inadequate employment, or welfare as the independent variable. Studies at the ecological level primarily use the unemployment rate. Results: In the studies that best establish causality, research indicates a moderate but significant adverse effect of job loss on individual depression symptoms, but the net population effect remains speculative. For suicide and antisocial behavior, individual- and ecological-level studies converge to suggest a moderate positive association with economic contraction. Although some research on substance abuse suggests procyclical effects, the majority indicate that job loss significantly increases the risk of heavy drinking and symptoms of alcohol abuse. For all outcomes, various characteristics of the population or the specific economic exposure studied can modify the overall association. Conclusions: The studies reviewed suggest that adverse economic transitions predict increased mental health problems, particularly depression, suicide, and substance abuse. The strength of the association, particularly when measuring the response of populations to contracting economies remains unclear.

Selection in utero: a biological response to mass layoffs.

Most research describing the biological response to unemployment appears appropriately motivated by clinical or public health concerns and focuses on death, disease, and medical care. We argue that expanding the work to include other outcomes could contribute to basic science. As an example, we use the response to mass layoffs to discriminate between two explanations of low ratios of male to female live births in stressed populations. One explanation asserts that ambient stressors reduce the ratio of males to females conceived. The other argues that the maternal stress response selects against males in utero. We show that selection in utero better explains the observed data. We conclude that human adaptation to the economic environment deserves scrutiny from a wider array of scientists than it now receives. Am. J. Hum. Biol., 2010.

A sex-specific test of selection in utero

We find support for the hypothesis that changes in the monthly odds of a twin among live-born males predict subsequent and opposite changes in the odds of a twin among live-born females. The hypothesis arises from the long standing argument that natural selection has conserved mechanisms by which pregnant women in stressed populations spontaneously abort fetuses least likely to yield grandchildren. Previous attempts to empirically test this argument focus almost entirely on males. We contribute to the literature by showing that, consistent with the logic of natural selection, maternal adaptations to environmental changes likely have effects on the survival of both male and female conceptuses and fetuses.

Gender-specific selection in utero among contemporary human birth cohorts

Much literature argues that natural selection has conserved mechanisms by which stressed females cull frail males in utero. This argument implies that males from low sex ratio birth cohorts should, on average, live longer than those from high sex ratio cohorts. Research reports such associations but these tests use completed lifespan as the outcome and, therefore, must end with cohorts born in 1913 because too many males survive from more contemporary cohorts to determine average lifespan. The empirical literature does not, therefore, address whether selection affects male mortality in contemporary cohorts. We apply time-series methods to monthly cohorts born in California between 1989 and 2003 to measure the association between the ratio of male to female live births and infant mortality, controlling for all forms of autocorrelation that induce spurious correlations. Consistent with theories of selection in utero, we find a positive correlation between cohort sex ratio and male infant mortality. The results suggest that natural selection conserved the stress mechanism in females to end the gestation of relatively less fit males and that this mechanism manifests itself in contemporary human societies.

The social environment and IL-6 in rats and humans

Inflammatory cytokine levels predict a wide range of human diseases including depression, cardiovascular disease, type 2 diabetes, autoimmune disease, general morbidity, and mortality. Stress and social experiences throughout the lifecourse have been associated with inflammatory processes. We conducted studies in humans and laboratory rats to examine the effect of early life experience and adult social position in predicting IL-6 levels. Human participants reported family homeownership during their childhood and current subjective social status. Interleukin-6 (IL-6) was measured from oral mucosal transudate. Rats were housed in groups of three, matched for quality of maternal care received. Social status was assessed via competition for resources, and plasma IL-6 was assessed in adulthood. In both humans and rats, we identified an interaction effect; early social experience moderated the effect of adult social status on IL-6 levels. Rats that experienced low levels of maternal care and people with low childhood socioeconomic status represented both the highest and lowest levels of IL-6 in adulthood, depending on their social status as young adults. The predicted interaction held for non-Hispanic people, but did not occur among Hispanic individuals. Adversity early in life may not have a monotonically negative effect on adult health, but may alter biological sensitivity to later social experiences.

Selection against small males in utero: a test of the Wells hypothesis

BACKGROUND The argument that women in stressful environments spontaneously abort their least fit fetuses enjoys wide dissemination despite the fact that several of its most intuitive predictions remain untested. The literature includes no tests, for example, of the hypothesis that these mechanisms select against small for gestational age (SGA) males. METHODS We apply time-series modeling to 4.9 million California male term births to test the hypothesis that the rate of SGA infants in 1096 weekly birth cohorts varies inversely with labor market contraction, a known stressor of contemporary populations. RESULTS We find support for the hypothesis that small size becomes less frequent among term male infants when the labor market contracts. CONCLUSIONS Our findings contribute to the evidence supporting selection in utero. They also suggest that research into the association between maternal stress and adverse birth outcomes should acknowledge the possibility that fetal loss may affect findings and their interpretation. Strengths of our analyses include the large number and size of our birth cohorts and our control for autocorrelation. Weaknesses include that we, like nearly all researchers in the field, have no direct measure of fetal loss.

Hormonal evidence supports the theory of selection in utero.

Antagonists in the debate over whether the maternal stress response during pregnancy damages or culls fetuses have invoked the theory of selection in utero to support opposing positions. We describe how these opposing arguments arise from the same theory and offer a novel test to discriminate between them. Our test, rooted in reports from population endocrinology that human chorionic gonadotropin (hCG) signals fetal fitness, contributes not only to the debate over the fetal origins of illness, but also to the more basic literature concerned with whether and how natural selection in utero affects contemporary human populations.

Natural selection in utero induced by mass layoffs: the hCG evidence

Evolutionary theory, when coupled with research from epidemiology, demography, and population endocrinology, suggests that contracting economies affect the fitness and health of human populations via natural selection in utero. We know, for example, that fetal death increases more among males than females when the economy unexpectedly contracts; that unexpected economic contraction predicts low secondary sex ratios; and that males from low sex ratio birth cohorts live, on average, longer than those from high sex ratio cohorts. We also know that low levels of human chorionic gonadotropin (i.e., hCG) measured in the serum of pregnant women predict fetal death. We do not, however, know whether male survivors of conception cohorts subjected to contracting economies exhibit, as theory predicts, higher hCG than those from other cohorts. We show, in 71 monthly conception cohorts including nearly two million California births, that they do. We thereby add to the literature suggesting that the economy, a phenomenon over which we collectively exercise at least some control, affects population health. Our findings imply that the effect arises via natural selection – a mechanism we largely ignore when attempting to explain, or alter, how collective choice affects our biology.

From Paradox to Disparity: Trends in Neonatal Death in Very Low Birth Weight non-Hispanic Black and White Infants, 1989-2004

OBJECTIVES To examine temporal trends in race-specific neonatal death in California to determine whether the overall decline in mortality attenuated the paradoxical survival advantage of very low birth weight (VLBW; birth weight < 1500 g) non-Hispanic black infants relative to VLBW non-Hispanic white infants. STUDY DESIGN The data set comprised the California birth cohort file on non-Hispanic black and non-Hispanic white VLBW neonatal mortality for 1989-2004. Logistic regression methods were used to control for potentially confounding maternal characteristics. RESULTS In 1989 and 1990, non-Hispanic black VLBW infants demonstrated a paradox of lower neonatal mortality (adjusted odds ratio [aOR] = 0.84; 95% confidence interval [CI] = 0.75-0.94). This survival advantage disappeared after 1991, however. In 2003 and 2004, the incidence of neonatal mortality increased in non-Hispanic black VLBW infants but decreased in non-Hispanic white VLBW infants, resulting in a racial disparity (aOR = 1.34; 95% CI = 1.14-1.56). CONCLUSIONS An initial survival paradox transformed into a disparity. The magnitude of this non-Hispanic black/non-Hispanic white VLBW disparity rose to its highest levels in the last 2 years of the study period. Moreover, the steady mortality increase in VLBW non-Hispanic black VLBW infants since 2001 reversed the secular decline in neonatal mortality in this population. Our findings underscore the need to augment strategies to improve the health trajectory of gestation in non-Hispanic black women.