The Goldilocks Principle of Stress: Too Little Is Almost As Bad as Too Much

Stress isn't all bad. You need just the right amount of adversity in life to learn to cope with the troubles ahead.

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A life free of stress and adversity sounds blissful. But, in fact, the happiest and healthiest people are those who have had at least some early exposure to negative experiences, according to a new research review.

Despite the popular notion, stress isn’t all bad. In fact, low to moderate amounts of stress are necessary for healthy growth. What’s harmful is large doses of uncontrollable stress — experiencing a natural disaster, for instance, or living in extreme poverty — particularly in early life. Also harmful, it turns out, is having experienced no stress at all.

The new review adds weight to a growing body of evidence that most brain systems function like muscles: they are strengthened through exposure to gradually increasing loads at the appropriate stages of development, but they will wither without exercise and get injured if they are suddenly overloaded without prior training. The stress system is a prime example.

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In one study included in the review, researchers interviewed 2,000 adults about their lifetime experiences with 37 negative events — things like serious illness or injury, parental divorce, death of a family member, natural disasters and physical and sexual abuse. Participants also provided information about how old they were when the various events occurred.

In addition, the participants were asked about their current levels of distress, their functioning at work and in their relationships, their symptoms of post-traumatic stress and overall life satisfaction. Participants were followed for two years.

Not surprisingly, the more negative experiences people had suffered in the past, the more distress, impairment and post-traumatic stress they reported, along with less satisfaction with life. However, the relationship wasn’t linear. “A history of some prior adversity was associated with better outcomes over time than not only a history of high prior adversity but also a history of no prior adversity,” the authors wrote.

In other words, there’s a sweet spot of stress: too much stress overloads the system and makes life difficult, but having had too little stress causes similar problems. It may be that people who have been through just enough hardship are best able to develop their abilities to cope — and have a more firmly established network of social support — making it easier for them to handle tough experiences later on.

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Another study looked at people with chronic back pain. Again, those who had either no previous adversity or high levels of it had worse function and used more medical services than back-pain sufferers who had experienced some life stress. Indeed, having had an adversity-free life was almost as bad as having had high levels of trauma in terms of disability and prescription pain medication use.

In another study, researchers gauged students’ experience of physical pain. The students were asked to submerge one hand in a bucket of freezing water and report how much pain they felt. Afterward, they were interviewed about their emotional experience during the task.

The researchers wanted to know whether the participants were “catastrophizing” the pain task. Catastrophizing involves thinking that the pain will be unbearable and overwhelming — which in turn heightens the perception of pain.

In this study, too, the researchers found that those who had had moderate exposure to adverse experiences were less likely to catastrophize and felt less pain and less associated negative emotion, compared with those with histories of high or no adversity. Catastrophizing itself, in fact, accounted for some of the increase in pain intensity and negative emotion seen in people on both ends of the spectrum.

That makes psychological sense: if you’ve experienced many disasters, it’s not surprising that you’d expect the worst, while if you’ve had a stress-free life, the novelty of pain itself may provoke intensified fear. In contrast, if your past experiences of stress have been manageable, new ones are less worrisome.

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So, does this mean you should deliberately expose your children to stressful experience to toughen them up? Mark Seery, assistant professor of psychology at the State University of New York at Buffalo, the author of the study, thinks not.

“Bad things are still bad things,” Seery writes, noting that the findings should not be taken to minimize the negative consequences of adversity. “This work does, however, suggest that experiencing adversity may have an upside — a silver lining — in that it may help foster resilience.”

For most people, life naturally includes enough stress that there’s absolutely no reason for parents to create more for their children. In fact, studies of “tough-love” programs aimed at promoting behavior change find that this is either ineffective or outright harmful.

For babies in particular, the research finds that responsive care — especially soothing them when they cry — is the best way to “educate” their stress systems. Infants first require nurture from caregivers in order to develop the ability to self-soothe. As they grow, however, they will require gradually increasing challenges — not too much, not too little. When it comes to stress, the Goldilocks principle seems to apply.

The research was published in Current Directions in Psychological Science.

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Maia Szalavitz is a health writer at TIME.com. Find her on Twitter at @maiasz. You can also continue the discussion on TIME Healthland’s Facebook page and on Twitter at @TIMEHealthland.