Has the heat got you down? You’re probably not alone.
Wintertime—with its long, dark nights—is the season most associated with low mood and depression. But sun-filled summer days can also bring on the doldrums, particularly for the subset of people who experience a summertime version of seasonal affective disorder (SAD)—a type of depression with a periodic pattern. Those with a lesser-known and lesser-studied summer SAD variant may feel “out of sync with the rest of the world” because they experience depression just as summer breaks and pool party invites pick up, says Thomas Wehr, a psychiatrist and scientist emeritus at the National Institutes of Health.
Depression can occur any time of year, but some research indicates that the warmer months can be particularly challenging for certain people. A growing number of studies indicate links between body temperature and depression, and high outside temperatures have been linked to mood and mental health crises. The prevalence of summertime SAD remains unclear, but as climate change makes extreme weather more common, understanding the effects of hot days on mental health—and developing new, effective treatments—has higher stakes.
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What Is Summer SAD?
Wehr and his colleague Norman Rosenthal, a psychiatrist then at the NIH, coined the term SAD in the early 1980s based on their research into people with cyclical winter depression. After publication, they received some unexpected letters from people who vehemently attested to having the opposite condition: depression in the summer and improved mood in winter.
Wehr and Rosenthal’s team investigated these accounts in a 1987 case report, which described 12 people who displayed a pattern of recurrent depressive episodes in the summertime. In a 1991 follow-up paper, they compared another 60 participants, half of whom seemed to have summer SAD and half of whom had winter SAD. Both groups met clinical criteria for depression that usually reoccurred seasonally, but the two cohorts experienced different symptoms.
Participants in the winter group “were very lethargic” and compared themselves to hibernating animals, says Rosenthal, who is now a professor at the Georgetown University School of Medicine. In contrast, the summer group was more “irritable” and “restless,” he adds. The winter cohort more frequently slept, overate and experienced weight gain, whereas the summer cohort reported higher incidences of insomnia, reduced appetite and more frequent weight loss.
The prevalence of summer SAD “would be a complete guess” because of limited data, Rosenthal says. Based on his interactions with people who do have the condition, Wehr believes it may be more common in warmer and more humid locations and in regions with limited access to air-conditioning. But Rosenthal and Wehr say much more work is needed to truly understand how common summer SAD is and where it most frequently occurs.
Compared with the winter variant, “the literature on summer SAD is much smaller,” says Kelly Rohan, a clinical psychologist who studies subtypes of recurrent depression at the University of Vermont. Both the 1987 and 1991 studies had a small sample size, and there has been minimal follow-up work. Nevertheless, Rohan says those early case studies are robust and convincing because they thoroughly examine and describe peoples’ symptoms.
Much research has linked winter SAD to shorter daylight hours and reduced sunlight exposure, causing clinicians to suggest light therapy as a potential treatment. In contrast, Rohan says, the primary triggers for the summer type are assumed to be heat and humidity.
Some researchers question whether SAD—either the summer or winter variety—should be a medically recognized condition altogether. “As it’s conceptualized, I am skeptical,” says Steven Lobello, a psychology professor at Auburn University at Montgomery. In 2016 Lobello and his colleagues published a study involving survey data from 34,000 people in the U.S. that found no population-level indication that depressive episodes were more common in the winter. A 2019 review found “some support for seasonal variation in clinical depression” but noted that prior research was “fragmented,” with varied findings.
Multiple studies have documented that heat can affect mood disorders and behavior, says Kim Meidenbauer, an assistant professor of psychology at Washington State University, who studies heat’s psychological effects. Increases in aggression and violent crimes have been well documented on hotter days and during summertime, Meidenbauer says. Recent studies have also found that psychiatric emergency room visits for depression and other mental health disorders peak on hotter days, mood trends more negative with increased heat and suicide rates rise in conjunction with temperature. The latter study on suicide risk, which was published in 2018, also found a decline in well-being corresponding to hotter outdoor temperatures, according to an accompanying analysis of depressive language in 600 million posts on Twitter (now X) between May 2014 and July 2015.
Rosenthal notes the findings about psychiatric hospital admissions, suicide risk and even online activity are in line with his previous work on SAD, which also concluded that people who face mental health struggles in the summer are more agitated than those who do so in the winter. People who are depressed but restless—with energy to spare—might be more likely to act on suicidal urges or end up in the hospital or, he explains.
Meidenbauer notes there are a few hypotheses for why heat might trigger depression. For one, “it interrupts your sleep,” she says—and quality shut-eye is critical for mental health. Maintaining a normal body temperature is also a resource-intensive process, Meidenbauer says. Heat can become a physical stressor, particularly for children, older people and those taking certain medications that disrupt the body’s ability to cool down. If people are uncomfortable over a long period of time, that invariably affects emotional state, she says.
One 2018 review study indicates that heat may also disrupt neurotransmitters involved in brain activity while we’re awake, which could contribute to depression. In addition, multiple studies have found that depressed people have an elevated body temperature, especially at night, which suggests depression itself may undermine the body’s ability to regulate temperature.
Wehr says investigating the relationship between temperature and mental health could help home in on the mechanisms underlying depression and even improve treatments, which is especially important because experts overwhelmingly agree that climate change is likely to exacerbate the mental health risks of hot weather.
Summer SAD Solutions
Treatments for summer depression are understudied, Rohan says. There is some evidence that lowering the body temperature via air-conditioning, cold showers or swimming sessions can help at least temporarily. In Rosenthal and Wehr’s first case report, one patient’s mood improved when Wehr recommended she try confining herself to an air-conditioned house and regularly taking cold showers, but she reported feeling depressed again just nine days after stopping this regimen.
Meidenbauer points out that staying indoors in heavily air-conditioned spaces and taking frequent cold showers likely isn’t sustainable from an environmental, practical or financial perspective. Swamp coolers and fans may be cheaper, more accessible options—particularly for that extra critical nighttime cooling.
Counterintuitively, exposure to high heat via saunas and hot tubs might offer longer-term relief. Some clinical trials have found that peoples’ depression improved when treated with hot baths. This could be because short-duration, high-intensity heat resets dormant or dysfunctional thermoregulatory systems in people with depression, says Ashley Mason, a clinical psychologist and an associate professor at the University of California, San Francisco. If people with summer SAD have thermoregulation issues, Mason suggests, such heat therapies may be especially helpful.
Beyond manipulating body temperature, simply tracking mood and comfort level throughout the summer season can be useful, Meidenbauer says. Noticing a pattern is the first step toward changing it, she adds. If you know that heat dampens your mood, that’s one more tool you can use to potentially predict, prepare for and mitigate (metaphorically) dark days. Rosenthal agrees. “Look at the things that make you feel better and do them more. And look at the things that make you feel worse and do them less,” he says. This tip can help people who experience mental health issues any time of year.
IF YOU NEED HELP
If you or someone you know is struggling or having thoughts of suicide, help is available. Call or text the 988 Suicide & Crisis Lifeline at 988 or use the online Lifeline Chat.
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