Sydney, June 2 (IANS) Smokers are more than twice as likely to have symptoms of depression as compared to non-smokers, research says.

A study by University of Otago involved over 1,000 people, who were asked at ages 18, 21 and 25 years about their smoking habits and whether they had symptoms of depression.

Sophisticated statistical analysis of results found that smoking increases the risk of developing depressive symptoms, rather than the other way round, says an Otago release.

David Fergusson, professor at Otago, who led the study, says: ‘Our findings are consistent with the conclusion that there is a cause and effect relationship between smoking and depression.’

‘The reasons for this relationship are not clear. However, it’s possible that nicotine causes changes to neurotransmitter activity in the brain, leading to an increased risk of depression,’ he adds.