Exposure to vitamin D could lower the risk of depression in children, according to a new study.

Children with higher levels of the vitamin have a 10 percent lower risk of developing the mental health problem.

Research from the Children of the 90s project at the University of Bristol shows that the link between low levels of vitamin D and depression is established during childhood.

Ensuring children have a good intake of vitamin D could help reduce depression in adolescence and adulthood, the research found.

While the link between depression and vitamin D has already been established in adults, this is the first study to look at the vitamin's effect in children.

The study examined vitamin D levels in more than 2,700 children aged nine and found that those with higher levels of the vitamin were 10 percent less likely to show signs of depression when they were tested again at the age of 13.

Those with higher levels were also more likely to show a decline in depressive symptoms between the ages of 10 and 13.

The study investigated levels of two forms of vitamin D - D2 and D3 - and found the strongest anti-depression link with D3.

Until now, it was unknown whether both forms of the vitamin were associated with depression.

The researchers stressed that the findings in themselves do not warrant changes in nutritional policy without further clinical trials. They also did not recommend the introduction of routine testing for vitamin D or that children should take supplements to prevent depressive symptoms.

"Given the importance of depression in childhood and adolescence and the relative ease with which vitamin D levels could be increased with supplements, randomised controlled trials to assess its effectiveness in preventing depressive symptoms would be appropriate," said Dr Anna-Maija Tolppanen, of the university's school of social and community medicine, who lead the study.

Vitamin D is provided by exposure to sunlight and from certain foods like oily fish and fortified breakfast cereals.

The research follows a recent study by the Institute of Opthamology at University College London, which found that an increased intake of vitamin D could significantly improve the vision of elderly people.