There is no question that depression is linked with eating disorders. In fact, as many as 59% of those with bulimia and 80% of those with the purging type of anorexia experience major depression at some time in their lives.

But the exact mechanism of the link between depression and eating disorders in children and adults -and even which problem precedes the other-remains an unanswered question. Some of the most common theories include:

• Biochemical Changes: The neuroendocrine system, which is the interaction between the nervous system and the endocrine glands that produce hormones, regulates many functions of the mind and body. Some of these include growth, appetite, sleep, emotions and thinking. Disturbances in this regulatory system, particularly in the function of certain chemicals in the brain that transmit messages from one nerve cell to another, may result in thinking and mood disorders as well as problems with appetite regulation. Two of these "neurotransmitters," seratonin and norepinephrine, have been found to function abnormally both in those with depression and those with eating disorders, leading scientists to believe that there is a link between the two problems.
  
  Teenagers and adults with anorexia and those with certain kinds of depression also have higher than normal levels of cortisol and vasopressin, two hormones that are released by the brain in response to stress. These hormones regulate many areas of thinking and mood.
  
  
• Changes In Relation to Malnutrition: The body needs a sufficient intake of nutrients to function properly; the normal response to insufficient food intake is a shutdown of body systems, including production of hormones. One example is tryptophan, which is an amino acid found in protein-rich foods such as turkey and eggs. When tryptophan levels are decreased, the production of serotonin is decreased, leading to mood and thinking problems.
  
• Psychosocial Problems- Adolescence can be a very unsettling time. There are often difficulties adapting to family problems, confusion related to conflicting messages from peers, adults and society, and pressures to succeed. Such emotional stressors can lead both to depression and to disturbances in eating.

Eating disorders and problems themselves can cause shame and guilt, and often a teen feels alone and isolated with this problem. This may ultimately result in depression.

Depression in teens, whether associated with eating problems or not, calls for prompt treatment. It's important to recognize warning signs of depression, which can include any of the following symptoms, especially if they last longer than two weeks:

• Declining performance at school
• Lack of interest in friends or activities previously enjoyed
• An overall sadness or expressions of hopelessness
• Restlessness, agitation, anger or rage
• Decreased energy level
• Lack of self esteem
• Decreased concentration or memory
• Changes in eating or sleeping
• Abusing substances
• Suicidal thoughts or gestures