Image copyright Science Photo Library Image caption The omega-three fatty acids in fish may be key to chemicals in the brain linked to depression

Eating a lot of fish may help protect against depression, research suggests.

An analysis of 26 studies of more than 150,000 people in total indicated a 17% reduction in the risk of depression among those eating the most fish.

One potential reason given by the researchers was the fatty acids found in fish may be important in various aspects of brain activity.

Mind, the mental health charity, said the study supported other work showing links between diet and mood.

Writing in the Journal of Epidemiology and Community Health, the Chinese researchers said many studies had been done looking at fish consumption and depression, but the results had been mixed.

When they looked at different study types, they found that the apparent protective effect of eating lots of fish was specific to studies done in Europe and not those from other areas of the world.

To try to come to a conclusion on what they said had been a controversial issue, they collated the data from all the relevant studies they could find conducted since 2001.

Their calculation did show a significant link between the two, and it was true for men and women.

While the results could not point to any conclusions about cause and effect, there were interesting theories as to why fish may be good for mental health, the researchers said.

Healthier diets link

One possible explanation is that the omega-three fatty acids found in fish may be key in the activity of dopamine and serotonin - two signalling chemicals in the brain thought to be involved in depression.

Another possibility is that people who eat a lot of fish may have a healthier diet in general - which in turn could help their mental health.

Prof Dongfeng Zhang, from the Medical College of Qingdao University, said: "Higher fish consumption may be beneficial in the primary prevention of depression.

"Future studies are needed to further investigate whether this association varies according to the type of fish."

Rachel Boyd, information manager at Mind, said they had recently published a guide, Food and Mood, which included advice on eating the "good fats" such as those found in fish.

"It is important not to oversimplify the results as there are lots of different factors in the development of depression," she said.

"But we really agree that having these fatty acids in your diet can be helpful, and it's something where people can make quite small changes that could have quite a big impact."

She pointed out that for vegetarians or others who did not want to eat fish there were other sources of fatty acids, such as seeds and nuts, as well as supplements.