The Health Risks of Evening Stress

Nighttime worrying may affect health more than morning nerves

If the last two decades of research have taught doctors anything, it’s that persistent and high levels of stress are harmful to human health.

Psychological stress contributes to a range of heart problems, from structural abnormalities to heart attacks. Studies have also found that chronic stress can disrupt the body’s immune and endocrine systems as well as its metabolic processes, and that these disruptions are associated with diabetes, irritable bowel disease, cancer, and other medical conditions.

Experts are focusing their attention on cortisol and hormonal changes in the body. Cortisol is often referred to as a “stress hormone” because its levels rise during periods of duress or anxiety. Along with helping the body prepare to meet a potential threat, cortisol also plays a role in settling down inflammation, says Darlene Kertes, a stress specialist and associate professor of psychology at the University of Florida. One of cortisol’s roles is to shift the activation of certain immune cells in ways that prevent inflammation from raging out of control. But when cortisol levels are chronically elevated, the hormone and immune systems that normally hold inflammation in check can get out of whack.

Preventing runaway inflammation isn’t cortisol’s only job. In healthy people, cortisol tends to rise and fall during the day in a predictable pattern. “Normally, the body’s cortisol levels peak about 30 minutes after we wake up,” Kertes says. Following this morning peak, levels usually decline steadily throughout the day before bottoming out shortly after a person falls asleep.

Kertes says cortisol’s daily rise and fall helps maintain the body’s circadian rhythms, which govern everything from sleep and appetite to cellular repair and maintenance. In the context of these normal, healthy patterns of cortisol activity, it would make sense that late-in-the-day stresscould cause a spike in the hormone when the body is supposed to be winding down. And preliminary research supports the idea that evening stress may be more harmful or disruptive to the body than morning stress.

A 2018 study from Hokkaido University in Japan found that the brain’s hypothalamic-pituitary-adrenal (HPA) axis, the network that manages the body’s stress response, reacts differently to morning stress. Specifically, the study found that cortisol spikes more acutely when a person is exposed to a stressor in the morning, compared to the evening.

If the body’s protective cortisol responses are dulled in the evening, it’s possible that long-term exposure to late-in-the-day stress may “exhaust” the nervous system in ways that promote health problems, including obesity, Type 2 diabetes, and high blood pressure, says Yujiro Yamanaka, an author of the study and an associate professor at Hokkaido University. He recommends avoiding stress in the evening whenever possible.

Even if the body adapts to evening and nighttime stress with an appropriate amount of cortisol, there could still be health implications. “If you’re continually stressed later in the day, this could disrupt the natural diurnal decline in cortisol, and that’s probably going to disrupt sleep,” Kertes says.

She says that long-term elevations in stress — not for a day or a week, but for months or years — are associated with a “flattening” of the body’s normal cortisol slope. “You see that morning cortisol levels are not as elevated, and evening levels aren’t as low,” she says. This sort of shift could throw off the body’s circadian rhythms in ways that contribute to a range of health issues.

A 2018 study from the University of Colorado found that cortisol levels tended to remain elevated in the evening among obese women, but not among “normal weight” women. And research has also found evidence that cortisol levels are elevated in the evening among people with major depressive disorder. There’s also a lot of evidence linking circadian disregulation to health problems.

But while it makes sense that the human body may be better equipped to deal with stress in the morning, Kertes says the jury’s out on whether the timing of stress really matters when it comes to health. Most of the evidence points to long-term levels of elevated stress as the most damaging, regardless of when it happens, she says. “It could very well be that morning and evening stress pose risks for different types of health problems,” she adds. “I don’t think it’s clear cut that one is worse than the other.”

“When people are stressed at night, we know that it disrupts their quality of sleep.”

Focusing on late-day stress and sleep yields more concrete risks. “When people are stressed at night, we know that it disrupts their quality of sleep,” says Christopher Fagundes, a stress researcher and associate professor at Rice University. Disrupted sleep is associated with almost any medical condition a person could name, including depression. “We also know that when people don’t sleep well, the next morning their blood pressure will be higher and inflammation levels will be higher,” Fagundes says.

Dealing with evening stress now and then is probably not a big deal, he says. But if this cycle repeats itself over and over again — every night a person is stressed, and every night sleep is disrupted — this could impact diurnal cortisol rhythms, among other things. Fagundes says the relationships among all these variables — sleep and stress and inflammation and cortisol — tend to be “bidirectional,” meaning one affects the other and vice versa in a kind of biological feedback loop. Evening stress can lead to poor sleep, which in turn can lead to a more pronounced stress response the next day, which may further disrupt sleep, and on and on.

While the research on the timing of stress is mostly preliminary, he says avoiding anxiety-inducing activities late in the day and especially before bed is a good idea. For a lot of folks, that may mean ignoring work-related email at night, which studies have linked to stress and poor health. Research has also found that nighttime use of “active” forms of technology — basically anything that involves communication with other people, whether it’s texting or using social media — can also disrupt sleep.

As Kertes says, the jury’s still out. But evening stress may eventually prove to be the most harmful stress of all.