Long-Term Effects of Stress

Two recent studies assessing the effects of stress on tree swallows could potentially show us the impact transient but acute stressful events – such as terror attacks and war – can have on the long-term health of humans, and also why some people are more prone to these effects than others. Both studies were conducted by Cornell University researchers, the first being published in the Proceedings of the Royal Society journal and the second in the Royal Society’s Biology Letters.

The First Study

The researchers exposed the tree swallows to the stress hormone glucocorticoid by dissolving it in a gel and putting it on the eggs in their nests. This led to only the female swallows incubating those eggs absorbing the hormone through their skin. The swallows were given five separate, hour-long doses of the hormone early on in their reproductive phases.

The findings of this study showed that the swallows exposed to the glucocorticoid gel fed their hatchlings at lower rates which led to their having reduced growth as well as lower survival rates.

Maren Vitousek, the first author of this study and assistant professor in Cornell University’s Department of Ecology and Evolutionary Biology says that these findings indicate that the birds’ exposure to these hormones – the  same hormones they would be exposed as a result of a short-term stressor –  do result in the long-term effects observed in the study. Vitousek also says that although this study was conducted on birds, the way other vertebrates such as humans physiologically respond to stress is quite similar, so these findings could also tell us something about the implications of short-term stress on long-term human well-being.

Source: Success Under Pressure

The findings of the study also showed that the birds exposed to higher doses of the glucocorticoid hormone were more vulnerable to the long-term effects of exposure. This, according to Vitousek, suggests that people who naturally have stronger hormonal responses to brief stressors may also be more vulnerable to the long-term effects of stress hormone exposure.

The Second Study

This study, led by first author and postdoctoral associate at Cornell University, Conor Taff, investigated the factors influencing vulnerability to stress and why the ability to cope with it differs between individuals. It was published in the Royal Society’s Biology Letters.

For this study, the researchers captured tree swallows and released them. They measured their baseline stress levels, how much they increased after capture, and how quickly they went back to normal. As with the first study, the birds were also exposed to glucocorticoids by the eggs on their nests. This time, the researchers also measured the baseline stress levels of the stress hormone in the birds, the spike caused by exposure, and how quickly the returned to normal.

The findings show that the birds that were more easily able to recover from the stress of capture also found it easier to recover from the glucocorticoid surge brought on by the gel. Vitousek believes that these findings indicate that people who are more resilient in the face of stress are more apt at “turning off” the stress response.

The take-home message? You’re better off taking things easy. Stress has a laundry list of unpleasant side-effects and this study just adds another.