Adults who tucked into the treat had 70 per cent lower odds of reporting depressive symptoms than those who ate no chocolate at all, the research showed.

The team studied data from 13,626 adults in the US and also found the 25 per cent who ate the most chocolate of any kind were less likely to report depressive symptoms than those who did not eat it.

But the survey was only a "snapshot" and further research is needed to confirm a link, experts have cautioned.

Lead author Dr Sarah Jackson, from University College London's Institute of Epidemiology and Health Care, said: "This study provides some evidence that consumption of chocolate, particularly dark chocolate, may be associated with reduced odds of clinically relevant depressive symptoms."

The team, who worked with the University of Calgary and Alberta Health Services Canada, found no significant link between not eating dark chocolate and depressive symptoms.

"Further research is required to clarify the direction of causation," Dr Jackson said.

"It could be the case that depression causes people to lose their interest in eating chocolate, or there could be other factors that make people both less likely to eat dark chocolate and to be depressed."

Data was gathered from the US National Health and Nutrition Examination Survey.

Adults' chocolate consumption was checked against their scores on the Patient Health Questionnaire, which looked at depressive symptoms.

Other factors including height, weight, marital status, ethnicity, education, household income, physical activity, smoking and chronic health problems were also taken into account to ensure the study only measured chocolate's effect on depressive symptoms.

The results were noted after the participants said whether they ate any dark chocolate in two 24-hour periods.

Researchers explained chocolate has been widely reported to have mood-boosting effects.

Reasons for the relationship include chocolate's inclusion of psychoactive ingredients which produce a feeling of euphoria similar to that of cannabinoid, found in cannabis.

It also contains phenylethylamine, a neuromodulator which is believed to be important for regulating mood.

Experimental evidence also suggests that mood improvements only take place if the chocolate is palatable and pleasant to eat, which suggests that the experience of enjoying chocolate is an important factor, not just the ingredients present.

Dr Jackson added if the effect on depression was causal, studying the biological mechanisms could reveal the ideal amount and type of chocolate to prevent the condition.

The team also pointed out dark chocolate has a higher concentration of flavonoids, antioxidant chemicals shown to improve inflammatory profiles which could play a role in the onset of depression.

Australian Associated Press