It has been informally recognized for years that in some individuals with bipolar disorder, symptoms tend to worsen during the sunny, hot days of summer. But is there now formal evidence to back up this claim?
There could be, in the form of new research from Taiwan that suggests high daily temperatures — above 75°F — are associated with increased hospitalization rates among patients with bipolar disorder, particularly women.
The study, conducted by researchers from National Cheng Kung University, looked at data from over 9,000 bipolar-related hospital admissions (among approximately 5,500 bipolar patients). Researchers noted a strong association between increased outside air temperatures over 75.2°F (24.0°C) and hospital admissions for bipolar disorder the following day. As the mercury outside rose, so did the number of patients admitted. Compared to days with more moderate temps, risk for bipolar admission increased 10%, 15%, 34%, and 51% when the daily mean temperature was over 75°F, 81°F, 84°F, and 87°F, respectively.
What’s more, researchers found that women with bipolar disorder were 48% more likely to be admitted to hospital as the temperature increased compared with men.
What’s the connection? Bipolar disorder is a common type of mood disorder characterized by alternating states of elevated mood, or mania, and depression. As previous research has shown, extreme ‘mood swings’ in bipolar disorder have been strongly associated with disruptions in circadian rhythms – the 24-hourly rhythms controlled by our body clocks that govern our day and night activity.
Because warm temperatures tend to coincide with the longer days of summer, it may be that people are more likely to stay up later, in general, or have trouble sleeping in the heat, and this is what sets off the changes in brain chemistry that worsen symptoms. Or it could be the heat itself that brings about brain changes — or something else entirely.
Researchers in Taiwan say their study supports the idea that environmental factors, specifically seasonal weather patterns, play a role in triggering symptoms of bipolar disorder, but need to conduct more research to pinpoint the underlying reason.
“Future research should focus on the impact of other environmental variables on psychiatric hospitalization, and specifically on precautionary perspectives on mental health promotion and risk evaluation,” writes lead researcher Huey-Jen Su and team from National Cheng Kung University in Tainan.
Circadian study: https://www.eurekalert.org/pub_releases/2012-03/uom-bcm031312.php