The researchers said this may be due to the presence of the artificial sweetener aspartame, which yesterday was provisionally given a clean bill of health by the European Food Safety Authority, following a review.
Making the link does not prove soft drinks cause depression.
But researcher Honglei Chen said: "While our findings are preliminary and the underlying biological mechanisms are not known, they are consistent with a small but growing body of evidence suggesting that artificially sweetened beverages may be associated with poor health."
The study found that those who had four cups of coffee a day were 10 per cent less likely to become depressed than non-coffee drinkers. Dr Chen said this may be due to the caffeine in coffee stimulating the brain.
The British Soft Drinks Association urged caution over the findings and pointed out that the scientists themselves said that more research is needed.
Previous studies have linked soft drinks to heart attacks, diabetes, weight gain, brittle bones and pancreatic cancer.
- DAILY MAIL