New research adds more weight to a link between smoking cigarettes and depression.
An article by researchers at Otago and Christchurch Universities has been published in the British Journal of Psychiatry.
The study used a sample of 1055 participants who were part of a group born in the Christchurch region in 1977. They were studied at ages 18, 21 and 25.
The paper found evidence of a significant relationship between nicotine-dependence symptoms and depressive symptoms at each age.
It says the findings are consistent with previous research that has concluded the relationship can't be explained by other reasons, such as common genes or environmental situations.