The ability of yoga to reduce anxiety and raise spirits is linked to a surge in a specific brain chemical, researchers say.

The chemical, known as gamma-aminobutyric acid or GABA, is responsible for regulating the nervous system. People with high anxiety levels have less GABA, research has shown.

Researchers at Boston University studied 19 people aged 18 to 45 who practised Iyengar yoga — a form of Hatha yoga that uses belts, buckles and props to complete a series of postures — for 60 minutes three times a week for 12 weeks. They were compared to another study group of 15, who walked for the same duration over the same time period.

Participants' moods and anxiety levels were assessed at weeks 0, 4, 8, 12, and magnetic resonance spectroscopy scans were taken of their brains at the beginning of the study, after the 12-week period, and immediately after a 60-minute yoga session.

The MRS scans, which are similar to magnetic resonance imaging scans, identify brain metabolities and tissues. In the study, they revealed that GABA levels increased in certain areas of the participants' brains who reported to be less anxious following their yoga sessions.

"The yoga subjects reported greater improvement in mood and greater decreases in anxiety than the walking group," reads the study.

The researchers believe that yoga stimulates an area of the brain known as the thalamus, which in turn increases GABA levels.

"The possible role of GABA in mediating the beneficial effects of yoga on mood and anxiety warrants further study," they write.

The study was published online Thursday in the Journal of Alternative and Complementary Medicine.