(HealthDay)—Hatha yoga is effective for reducing anxiety, and efficacy increases with increasing number of practice hours, according to a meta-analysis published online May 20 in the Journal of Evidence-Based Medicine.

Stefan G. Hofmann, Ph.D., from Boston University, and colleagues conducted a meta-analysis of 17 studies to examine the effect of Hatha yoga on . Data were included for 501 participants who received Hatha yoga and reported before and after yoga.

The researchers found that the pre-post within-group and controlled were Hedges' g = 0.44 and 0.61, respectively. There was a positive association for treatment efficacy with the total number of hours practiced. Yoga was most beneficial for people with elevated levels of anxiety. Study year, gender, presence of a medical disorder, or age did not moderate effect sizes. The quality of studies was relatively low, but the effect was not moderated by risk of study bias.

"Hatha yoga is a promising method for treating anxiety," the authors write. "However, more well-controlled studies are needed to compare the efficacy of Hatha with other more established treatments and to understand its mechanism."