Low levels of physical activity and obesity are a strong predictor of depression, but being overweight may also pose a two-way risk, it has been claimed.

Depression could also be the cause of obesity as much as being overweight can lead to mental disorders and be linked to a lack of exercise, according to researchers from the University of Adelaide.

Commenting on a recent paper published in the British Medical Journal, University College London professor Mika Kivimaki explained that it is important to understand the bidirectional risk of obesity and common mental disorders.

He added that physical activity and other lifestyle factors may also play a role in the "complex inter-relationship between obesity and mental illness".

Professor Kivimaki said: "Obesity is associated with socioeconomic disadvantage and low levels of physical activity, both of which are strong predictors of depression.

"Obesity may constitute a chronic stressful state, which in turn can cause significant physiological dysfunction."

Using fitness equipment and other exercise techniques were recently highlighted as an important way to avoid seasonal affective disorder, also known as winter depression, by FitFarms.