Researchers have been puzzling over the apparent weight-mental health connection for years.

There's no question that obesity and depression are linked in both adolescents and adults. But does depression cause obesity, or does obesity prompt depression? Doctors are trying to get to the bottom of that relationship, so they can craft effective treatments for both conditions.

Obesity causes depression. Studies have shown that obese people are about 25 percent more likely to experience a mood disorder like depression compared with those who are not obese.

Obesity can cause poor self-image, low self-esteem, and social isolation, all known contributors to depression. Those who are obese can also find themselves ostracized, stereotyped, and discriminated against. The extra weight carried around by obese people can result in chronic joint pain as well as serious diseases like diabetes and hypertension, all of which have been linked to depression.

The age of loneliness is killing us

Depression causes obesity. A study of adolescents in Cincinnati found that teenagers with symptoms of depression were more likely to become obese within the next year. The study also found that kids who were borderline obese and depressed became substantially obese over the following year.

People experiencing depression are more likely to overeat or make poor food choices, avoid exercising, and become more sedentary. Researchers have found that depressed people with decreased levels of the hormone serotonin also have a tendency toward obesity — they tend to eat in an attempt to self-medicate and restore their serotonin levels to normal.

CDC Reports Depression and Obesity May Be Linked

Depression and obesity share common risk factors. Some factors apparently can trigger both obesity and depression. Belonging to a lower socioeconomic class and not participating in physical activity increases risk for developing either condition.

Certain behaviors could also increase obesity risk, including such sedentary behaviors as watching TV alone, playing video games and spending hours on the computer. All of these activities can lead to social isolation as well as weight gain. Numerous antidepressants have also been known to cause weight gain, as well. Yet researchers noted that they found a correlation and not a cause-and-effect relationship.