An longitudinal study of people who participated in Vasloppet, the world’s largest long-distance ski-race, held in Sweden showed that those participating in the race have lower incidence of bipolar disorder compared to the general population.
However, when performance in the race was considered, high performance women had higher risk of bipolar disorder than slower skiing women. This association was not found in men. The study was published in the International Journal of Bipolar Disorders.
Bipolar disorder is a complicated diagnosis. Its key feature are mood swings ranging from severely depressed to overactive manic episodes. Around 2-4% of the population are estimated to suffer from it.
The disorder typically begins with one or several depressive episodes, but these are later followed with at least one episode of mania or hypomania. Mania is a condition in which a person displays an over-the-top level of activity or energy, mood or behavior. It is characterized by feelings of invincibility, lack of sleep, racing thoughts and ideas, rapid talking and having false beliefs or perceptions.
Recent studies have linked bipolar disorder to around 10-year shorter life expectancy, for both men and women. This has been attributed to poor cardiovascular health and an increased risk of suicide of persons suffering from bipolar depression. Because bipolar disorder affects how energetic a person feels, many researchers have wondered whether exercise could have some bearing on the likelihood of developing bipolar disorder.
A large study in Sweden found people with the lowest fitness levels to have a higher risk of bipolar disorder. But are there any associations with an active lifestyle in general?
“Previous studies suggested that the preventive potential of physical activity for mental health could be substantial,” said study author Martina Svensson, an assistant researcher at Tomas Deierborg’s Experimental Neuroinflammation Laboratory at Lund University. “We were both interested in investigating this at a larger level.”
“As we previously have shown that having a physically active lifestyle is associated with around a 50% lower risk of developing depression and a 60% lower risk of developing anxiety disorders, we thought it could be interesting to investigate if physical activity could also have preventive potential when it comes to more complex psychiatric disorders such as bipolar disorder.”
“Our research team initiated a new project to investigate how physical activity affects brain disorders when I started my PhD project in 2013,” Svensson explained. “With my background in molecular biomedicine, the thesis project initially focused on investigating the molecular mechanism behind the potential beneficial effects of physical activity in animal models of brain ischemia and Alzheimer’s disease.”
“As Deierborg has participated in the Vasaloppet ski race two times before, he got in contact with Ulf Hållmarker (at that time the chief physician for the Vasaloppet ski race) and Stefan James, who initially set up the whole Vasaloppet registry to get data on this and compare with the less physically active general Swedish population. With this collaboration, we added an epidemiological perspective to our experimental exercise focus.”
Svensson and her colleagues analyzed the data on people who have participated in the Vasloppet ski race in Sweden between 1989 and 2010, a total of 197,685 individuals. They were compared with a group of non-skiers of equal size who were matched for age, region of residency and age, making the total number of people included in the study 395,369.
Participants in this race are known to smoke less, have more leisure-time physical activity, a healthier diet and lower mortality than the general population. To try to match this, researchers excluded from the comparison group individuals of poor health, those who could not participate in the race even if they wanted to and also persons with various serious health conditions. They monitored the finishing time of the skiers i.e., how long it took them to finish the race. Data on psychiatric and other health conditions of the persons included in the study were taken from the Swedish National Patient Registry.
Results showed that there were more than twice as many people with bipolar disorder in the non-skier group than in the group of skiers. “Both men and women who participated in the ski race had a lower incidence of bipolar disorder. The results remained significant even if all individuals developing any psychiatric disorders within 5 years of inclusion were excluded,” the researchers report.
“Those having a physically active lifestyle (being a skier in our study) had around 50% lower risk of developing bipolar disorder compared to the general population during the up to 21 years long follow-up in our study,” Svensson told PsyPost.
The researchers also examined whether the risk of bipolar disorder was associated with the time skiers needed to finish the race i.e., how fast they skied. Results showed that skiing speed in the race had no impact on the risk of bipolar disorder in men. In contrast, women who were the quickest to finish the race had more than twice higher chance of having bipolar disorder that women who were slower skiers.
“What surprised us the most was to discover how the physical performance in the ski race (finishing time of the race among the skiers) impacted the risk of future bipolar disorder differently in physically active men and women,” Svensson explained to PsyPost. “In men, the finishing time of the race did not significantly impact the risk of bipolar disorder.”
“We were surprised to see that physically high-performing women had almost a doubled risk of developing bipolar disorder compared to lower-performing women. In men, the finishing time of the race did not significantly impact the risk of bipolar disorder. So it seems like both sexes benefit from being physically active, even though the optimal level may differ between men and women.”
But the study, like all research, includes some limitations. For example, it did not manage to match the two groups on all factors – the group of skiers smoked less and had a better diet than non-skiers. Also, it did not include any measure of physical activity outside the participation in the ski race and there was no way to control for the family composition of participants or genetic factors.
“Our study does not control for diet and other lifestyle habits that may be linked to an active lifestyle,” Svensson explained. “Furthermore, our study does not investigate why faster skiing is associated with an increased risk of developing bipolar disorder compared to slower skiers among women. Hence future studies considering the impact of exercise intensity on the risk of developing bipolar disorders in men and women separately are warranted, especially with designs allowing for conclusions about directionality and causality of the association between physical activity and bipolar disorder.”
“Exercise behaviors and onset of bipolar disorder are likely to be affected by genetics, psychological factors, and personality traits, confounders that were not possible to investigate in our cohort. Also note that our study is an epidemiological study, where you can find interesting associations, but you cannot really scientifically prove the causation.”
Despite the limitations, the study provides important insights into the link between physical activity and bipolar disorder.
“Our study is important because it is the largest population-based study to date, confirming a long-term association of a physically active lifestyle on the later development of bipolar disorders in both men and women seen in previous studies with shorter follow-up times,” Svensson said. “In addition, our study reveals an association between physical performance and the risk for bipolar disorder in women specifically has not (to our knowledge) been reported before.”
“Currently, we are working on establishing an updated version of our cohort, including an even larger study population with follow-up times up to 36 years after participating in the ski race,” the researcher added. “In the new cohort, we plan to include also other types of physical activities, such as biking and running as well as additional data on socioeconomics, fitness level and cognitive capability. We look forward to following up on the findings we made in the previous cohort, taking new factors into consideration.”
The paper, “A physically active lifestyle is associated with lower long-term incidence of bipolar disorder in a population-based, large-scale study”, was authored by Martina Svensson, Sophie Erhardt, Ulf Hållmarker, Stefan James and Tomas Deierborg.
