Major depression is a leading cause of disability globally and according to American researchers people who are obese are more at risk of suffering from a psychiatric disorder.

The researchers who studied more than 9,000 people say there is a strong link between obesity and mood and anxiety disorders, especially among Caucasian Americans.

They have found that an obese person is about 25 percent more likely than a non-obese person to have a mood or anxiety disorder, such as depression and in those with more education and higher income, that risk may be as high as 44 percent.

The researchers from Harvard Medical School say the link between obesity and a range of common mood and anxiety disorders in the general U.S. population, is substantial but it is unclear which precedes the other.

Lead author Dr. Gregory Simon, a psychiatrist at Group Health Co-operative in Seattle, suggests it could be either.

The researchers say rising rates of obesity will produce an “unprecedented decline in life expectancy in the United States”, and obesity has been linked to a long list physical problems including heart disease, stroke, type 2 diabetes, high blood pressure, arthritis, kidney stones and certain cancers.

But its impact on the psyche is not as well documented.

The study which was part of a large national survey of mental disorders in the U.S. took the form of interviews with 9,125 people between February, 2001, and February, 2003.

Mental disorders were assessed using a World Health Organization diagnostic procedure and disorders such as major depression, bipolar disorder, anxiety disorders such as panic disorder, agoraphobia without panic, or generalized anxiety disorder and substance-use disorders were included.

The average age of the participants was 45.

It was seen that people with a BMI, or body mass index, of 30 or higher, were about 25% more likely than those with a BMI under 30 to have a mood disorder.

This equates to a link with almost one-quarter of the cases of obesity in the general population with a mood disorder.

The researchers suggest that a lifetime risk of depression of 20%, becomes a 28% risk in those who are obese and among those with post-secondary education, the risk may be as high as 44%.

Dr. Simon says the results are significant and even modest associations have a public health significance because of the high rates of obesity and mood or anxiety disorders in the general population.

Common symptoms of depression include increased appetite and weight gain and unfortunately the drugs used to treat depression or anxiety disorders can also lead to weight gain.

The research is published in the current issue of the journal Archives of General Psychiatry.