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Thursday, May 12, 2005

NATURAL SELECTIONS

KEEPING STRESS IN THE FAMILY

Fetuses found to inherit mother's trauma


Stress can motivate us, but it can also get us down. And though it might just make us feel blue, it can also kill us. It depresses levels of sex hormones and people stressed by deadlines are more likely to suffer heart attacks.

In Japan, karoshi (death by overwork) is said to claim 10,000 lives each year. Meanwhile in Britain last November, the Trades Union Congress, the national trades union organization, released data showing that stress costs the economy £7 billion a year.

With all the understandably negative reports about the effects of stress, it's easy to overlook the fact that the stress response is beneficial. And, like everything else to do with our bodies, the way they work and the way we behave, the stress response evolved through natural selection.

The stress hormone cortisol causes a rise in blood pressure and blood glucose levels. This is useful when an organism faces possible danger or loss of resources. It prepares us for "fight or flight," or -- in the modern world -- it helps us, say, to get a column written in time or to get through a public speaking engagement.

Cortisol is secreted when there are special opportunities as well as potential dangers. But when there are extreme dangers, cortisol levels can actually fall, because so much of it is used up. One of the consequences is a depressed immune system.

Cortisol levels can also fall if stress is chronic, drawn out, relentless. This was the kind of stress experienced by Yuji Uendan, a 23-year-old temporary staff agency employee who worked 9 3/4 hour shifts at a Nikon Corp. plant in Kumagaya, Saitama Prefecture, for 15 days in a row before committing suicide in March 1999. A Tokyo District Court ruling in March 2005 ordered Nikon and Atesuto (formerly Nekusuta), the Nagoya-based agency, to pay Uendan's mother 24.8 million yen compensation for her son's karoshi, in what is believed to be the country's first such ruling related to a temp service worker.

However, despite the recent increased awareness of the danger of stress, it is not just a symptom of the modern age.

If anything, stress was harsher in prehistory and had just as serious consequences as it does now. This was clearly seen in a study on wild primates in Madagascar, published earlier this year. High-stress animals were six times more likely to die than low-stress animals during a two-year study. The animals weren't captured (imagine how that would add to their stress), but their stress levels were measured by analysis of fecal glucocorticoid levels. Glucocorticoids are hormones similar to cortisol that help the body to cope with stress.

Biologist Ethan Pride, of Princeton University, N.J., who conducted the research, said that the technique will be useful for wildlife managers to identify at-risk animals and focus conservation efforts on them.

Few biologists would be keen to collect human feces and measure them for stress hormones, and thankfully there are easier ways. One method measures stress by analyzing cortisol in saliva. The results of such research are making scientists to re-evaluate the causes of stress.

It used to be thought that reduced cortisol levels could be explained by mostly environmental factors, such as the stress of living with a parent who is depressed or anxious. That was how researchers explained the low cortisol levels in the adult children of Holocaust survivors: The children had heard stories of how their parents suffered, and became traumatized themselves.

But after 9/11, researchers at Mount Sinai School of Medicine in New York City saw a different pattern. The scientists studied 38 women who were pregnant and witnessed the attacks on the World Trade Center. Those women in the sample who developed post-traumatic stress disorder (PTSD) symptoms in response to 9/11 had lower cortisol levels than the women who did not develop PTSD.

Such a result was what the scientists expected.

However, about one year after birth, the babies of mothers who had developed PTSD symptoms had significantly lower cortisol levels compared to those in babies of mothers who developed only minimal symptoms. .

"The findings suggest that mechanisms for transgenerational transmission of biologic effects of trauma may have to do with very early parent-child attachments," said Mount Sinai's Rachel Yehuda, "and possibly even in utero effects related to cortisol programming."

In other words, the reduced cortisol in babies seems to be a "transmitted" biological trait -- traumatized mothers may have passed on potential mental illness to their unborn children.

The Mount Sinai researchers, working with others at the University of Edinburgh, have found that this decrease is apparently passed on to children in the womb. The work is published in May's issue of the Journal of Clinical Endocrinology and Metabolism.

The findings strengthen the evidence for in utero or early-life risk factors for the later development of adult mental or physical disorders. These can cause a "ripple effect" of stress in the next generation.

But it is worth emphasizing that, to fully understand a physiological response, it is necessary to consider the evolutionary history of the response -- its function in evolutionary terms.

A book of Natural Selections columns translated into Japanese, "Nou to sekkusu no seibutsugaku (Evolution, Sex and the Brain)," is published by Shinchosha. Rowan Hooper is a biologist at Trinity College, Dublin. He welcomes readers' questions and comments at rowan.hooper@tcd.ie


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