Physical exercise should be a treatment option for people with mild depression, which affects as many as one in 10 British adults, according to the study by experts at Edinburgh and Stirling universities.

Until now the effects of basic activities such as walking have remained unclear, but the researchers, in a review published in the journal Mental Health and Physical Activity, analysed data from eight studies considering the impact of "walking interventions" on 341 patients.

PhD student Roma Robertson of Stirling University said yesterday: "Walking has a statistically significant, large effect on the symptoms of depression in some populations and is as effective as other forms of physical activity."

She added: "There has been a big movement towards encouraging people to walk for physical health reasons, but this study recognises its role in mental health and highlights a widely acceptable and safe treatment option.

"People working in primary care have a limited range of options as to what they can offer people with depression, and treatments such as anti-depressants aren't always effective and come with potential side-effects."

The researchers now plan to identify how long, how fast, and how often, to walk for depression, and whether walking indoors or out, or in a group, is more helpful.