(CNN) Weekly sessions of yoga may ease depressive symptoms in people with other mental health issues, according to a systematic review and meta-analysis of existing research.
"This is a great result to now encourage people who might be thinking about trying yoga that there's some scientific evidence that it can be effective for helping reduce depressive symptoms," said exercise physiologist and study author Jacinta Brinsley, a doctoral candidate at the University of South Australia.
Depression is often associated with other mental health conditions. For example, 20 to 40% of people diagnosed with schizophrenia and 72% of people diagnosed with lifetime anxiety also suffer from depression.
"Exercise has always been a great strategy for people struggling with these feelings as it boosts both mood and health. But as gyms and exercise classes of all kinds are now closed," Brinsley said, "people are looking for alternatives, and this is where yoga can help."
The new analysis, published Monday in the British Journal of Sports Medicine, reviewed 19 randomized controlled clinical trials, considered one of the higher-quality methods of research, conducted in the United States, India, Japan, China, Germany and Sweden.
People in the studies had a formal diagnosis of alcohol dependence, depressive and bipolar disorders, a psychosis such as schizophrenia or post-traumatic stress syndrome, called PTSD.
Participants did an average of one to two weekly yoga sessions between 20 and 90 minutes long, in which at least half the session was physical movement.
"This is any kind of yoga where asana — postures and movement — are the main focus," Brinsley said. "Most yoga classes that are delivered in gyms or studios today in Western society would fit this criteria. The most common styles would be: Vinyasa, Iyengar, Ashtanga and Power Yoga."
Yoga sessions were continued for an average of 2.5 months in the studies.
The results showed that yoga moderately eased depressive symptoms compared with no or self-help treatment across the mental health spectrum, with some conditions benefiting more than others.
The study found a moderate reduction in depressive symptoms for people diagnosed with depressive disorders and a significant reduction for those with schizophrenia. There was a small effect on alcohol use disorders but no impact on depression associated with PTSD.
For those that it helped, the more yoga sessions a person did each week, the less depressed they became, according to the analysis.
"The study's findings suggest that the more yoga you do, the better the effect. Although we don't know the exact 'dose' you need, those who did more yoga sessions per week had greater reductions in depressive symptoms," said Laurie Hyland Robertson, the editor in chief of Yoga Therapy Today, a journal published by the International Association of Yoga Therapists.
Because yoga was more effective as part of some diagnoses like schizophrenia and anxiety than others, such as PTSD, the results underscore "the importance of working with a professional who can tailor yoga practices to the individual, adapting the care plan as needed," said Robertson, who was not involved with the study.
Yoga, of course, is a form of physical exercise, and exercise is widely recommended to help ease depression and other mental health conditions. Scientists believe exercise increases blood circulation to the brain, especially areas like the amygdala and hippocampus — which both have roles in controlling motivation, mood and response to stress.
"We know that exercise is effective for improving mental health through a number of mechanisms, one of which is endorphins," the body's feel-good hormone, Brinsely said.
Other possible mechanisms, she said, are regulation of the body's central stress response system, called the hypothalamic-pituitary-adrenal axis, as well as yoga's impact on improving sleep quality and the increase in social interaction that yoga classes can bring.
But yoga is also a spiritual discipline, designed to meld body and mind. A yoga lifestyle incorporates physical postures, breath regulation and mindfulness through the practice of meditation.
"Yogic philosophy teaches that the body, mind and spirit are all interconnected — what you do in one area, for example, a physical exercise to strengthen your leg muscles, will have an effect in all of the other areas of your system," said Robertson, who coauthored the book "Understanding Yoga Therapy: Applied Philosophy and Science for Health and Well-Being."
"So we can expect that leg exercise, especially when you approach it in a mindful, purposeful way, to affect not only your quadriceps but also your emotional state, your body's physiology and even your mental outlook," she said.
Psychophysiological benefits of yoga have been studied since the early 1900s, finding the practice can reduce stress, regulate emotion, boost mood and instill a sense of well-being.
Stress reduction and mood regulation are obviously key to improving all sorts of mental health problems, so therapists began incorporating yoga into their treatment plans.
Much of the early research on yoga as therapy occurred in India, but today research has occurred around the world. Studies have explored the benefits of yoga therapy for anxiety, depression and schizophrenia, as well as post-traumatic stress disorder (PTSD) and obsessive-compulsive disorder.
A 2018 review of more than eight studies of 300 people, for example, found yoga may reduce high anxiety levels, but only short-term. An earlier 2013 study found more benefit for anxiety when interventions included at least 10 yoga sessions.
And a 2019 review concluded adding yoga to existing therapy can help with treatment of anxiety disorders, particularly panic disorder.
The National Institutes for Health, however, said that many of the studies that have been done on yoga included "only small numbers of people and haven't been of high quality. Therefore, in most instances, we can only say that yoga has shown promise for particular health uses, not that it's been proven to help."
Brinsley said the new analysis however, differs from previous reviews as it includes a range of mental disorder diagnoses and thus provides a more comprehensive assessment of the potential benefits for depressive symptoms.
"A study like this one is definitely exciting for those of us in the professional yoga world," Robertson said.
"We know that many people with depression don't get better, or don't get completely better, with medications or other traditional therapie — or they don't want to use these treatments for a variety of reasons — so effective options to complement existing methods are urgently needed to help people suffering with depression."