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There has been considerable research over the past decade showing correlations between long-term chronic stress and elevated levels of the stress hormone cortisol in humans. There has also been considerable evidence linking elevated cortisol levels to serious medical conditions like heart disease, hypertension, diabetes and cancer, and to memory and cognition problems. However, a new study, “Maternal Stress and Child Outcomes: Evidence From Siblings,” by Anna Aizer, Laura Stroud and Stephen Buka, has found a direct link between in-utero exposure to cortisol and the cognition, health and educational attainment of the exposed offspring.
The study, which compared 1093 children born between 1959 and 1965, found that elevated levels of cortisol in utero significantly affected their verbal IQ and health at age seven. Children born to mothers with elevated levels of cortisol also had worse birth outcomes and slightly lower levels of adult educational attainment and verbal cognition than siblings who had lower exposures to cortisol. For example, siblings exposed to very high levels of cortisol had an average IQ that was 5 points lower than their siblings and nearly half a year less schooling, and a 48% increase in chronic health conditions.
The researchers also found that lower income mothers had higher and more variable levels of cortisol and that they suffered more acute effects from elevated cortisol levels than affluent mothers. Because their cortisol and stress levels varied over time, the researchers were able to compare siblings who had been exposed to different cortisol levels in utero. This methodology reduced variation due to short term stresses and controlled for unobserved differences between different mothers that could have led to biased results.
While this research is compelling in terms of the effects of maternal stress on children’s physical and mental health and their future academic success, the authors take a huge sociobiological leap by arguing that their results may be part of the reason why children of poor parents tend to become poor adults themselves. Indeed boys born to parents in the bottom quintile for income have a 42% chance of remaining there when they grow up and only a 5% chance of moving up to the top quintile (Corak, 2004; Solon, 1999). However, there are numerous reasons why there is little social mobility in the U.S. that have nothing to do with biology, including an entrenched system of governance, taxation and commerce that ensures that the wealthy and their families will retain and increase their wealth and that makes it extremely difficult for the rest of us to significantly improve our socioeconomic status.
The study’s authors note that the poor report a greater number of stressful events in their lives (Dohrenwend, 1973; Marmot and Smith, 1991), while researchers have measured higher levels of the stress hormone, cortisol, in their bloodstreams (Cohen et. al., 2006; Steptoe et al, 2003; Kunkz-Ebrecht). This might seem counterintuitive in light of the stereotype of the highly stressed Type A businessman. However, bosses and the affluent have far fewer financial worries and those they have are on a completely different scale (e.g., whether or not to refinance their home or buy out a competitor versus how to make rent this month and avoid the homeless shelter or how to obtain enough money for dad’s diabetes drugs). Furthermore, wealthier individuals tend to have jobs in which they have higher status, greater respect and, most importantly, greater control over their responsibilities and time. Lower income people tend to have jobs with multiple bosses who may give conflicting orders. They tend to have less job security, which can force them to accept more abuse and degradation at work just to hold onto their jobs and meager incomes. And the wealthy tend to have much more disposable income to purchase (and time) to enjoy luxury and convenience items, travel, and recreational activities, which can relieve the stress they do suffer.
Even if maternal stress turns out to be a major contributor to socioeconomic immobility or poor educational outcomes, it is unlikely that there will be an adequate biological or medical solution. Prozac may make a person feel less gloomy, but it does not cause the boss to pay more or the landlord to lower the rent.
Of course it would likely help if, as a society, we ensured that all families received adequate perinatal care, including sufficient and nutritious food, exercise, medical care, relaxation, leisure and mental health support. As it is, the poor have a significantly higher chance of having a premature baby or one that is born with low birth weight. This is likely due to a combination of factors that include greater stress, as well as lack of health insurance and low-cost health clinics, the high price of healthy foods, overwork and access to paid family leave.
Cohen, Sheldon, Schwartz, Joseph, Epel, Elissa, Kirschbaum, Clemens, Sidney, Steve
and Teresa Seeman (2006) “Socioeconomic Status, Race and Diurnal Cortisol Decline in
the Coronary Artery Risk Development in Young Adults (CARDIA) Study”
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Corak, Miles (2004). “Do Poor Children Become Poor Adults? Lessons for Public Policy
from a Cross-Country Comparison of Earnings Mobility.” UNICEF Innocenti Research
Center, Florence, Italy.
Dohrenwend, Barbara S. (1973) “Social status and stressful life events” Journal of
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Kunz-Ebrecht, Sabine, Kirschbaum, Clemens and Andrew Steptoe (2004) “Work Stress,
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Solon, Gary (1999) “Intergenerational Mobility in the Labor Market” Handbook of Labor
Economics, Vol 3, Eds Orley Ashenfelter and David Card.
Steptoe, Andrew, Kunz-Ebrecht, Sabine, Owen, Natalie, Feldman, Pamela, Willemsen, Gonneke, Kirschbaum, Clemens, and Michael Marmot (2003) “Socioeconomic Status and Stress-Related
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