Sugar may be bad not only for your teeth and your waistline, but also your mental health, claimed a study Thursday that was met with skepticism by other experts.

Researchers at University College London (UCL) compared the reported sugar intake of more than 8,000 people in a long-term British study, to their mood.

The study participants, civil servants, were monitored from 1985-1988, and filled out a questionnaire every few years thereafter.

Researchers examined data from that study for an association between sugar intake and "common mental disorders" (CMD) such as anxiety and depression.

The UCL team found "an increased likelihood" for men with a higher intake of sweet foods and drinks to develop CMD after five years, and a general "adverse effect" on mental health for both sexes.

And they concluded, in a study published in the journal Scientific Reports, that "lower intake of sugar may be associated with better psychological health."

But dietician Catherine Collins, a spokeswoman for the British Dietetic Association, said this recommendation was "unproven."

Problems with the study, she said, included that sugar consumption was self-reported, and that sugar intake from alcohol was not counted.

The researchers, she said, appeared to confuse naturally-occurring sugar from foodstuffs such as milk, and "free sugars" added to hot drinks or in sweets.

"The dietary analysis makes it impossible to justify the bold claims made by the researchers about sugar and depression in men," Collins said via the Science Media Centre in London.

"Reducing intake of free sugars is good for your teeth, and may be good for your weight, too. But as protection against depression? It's not proven."

Nutrition expert Tom Sanders agreed the results should be interpreted "with caution".

"From a scientific standpoint it is difficult to see how sugar in food would differ from other sources of carbohydrate on mental health as both are broken down to simple sugars in the gut before absorption," he said.