Depression

Mental state marked by melancholy, pessimism or dejection accompanied by loss of interest in surroundings and lack of energy, appetite and sex drive.

Persons most commonly affected: Late adolescence or early adulthood in both sexes, with women twice as likely as men.
Organ or part of body involved: Brain
Symptoms and indications: Mood variations from mild depression to blank despair are usually the first symptoms. This is followed by insomnia, headaches, backaches, lack of sex drive, suicidal thoughts, fatigue, anxiety, loss of appetite, constipation are accompanying symptoms. The person may sit quietly, bowed, immobile, sometimes weeping silently. In severe cases the sufferer may experience hallucination or delusions.
Causes and risk factors: The growing complexities of modern life and its resultant crises, as well as mental stress and strain of day-to-day life, usually leads to this disorder. Medications, including corticosteroids, antihistamines, blood pressure medications, anti-inflammatory drugs, narcotics, and some pharmaceutical antidepressants can also cause depression. Preexisting conditions - most commonly hypoglycemia, anaemia, sleep apnea, low adrenal function, and thyroid gland malfunctions are also some causes.
Prevention: Avoid coffee, sugar, alcohol, and dairy products. Depression has been associated with a high intake of caffeine. If you drink four or more cups of caffeine in a given day, try substituting decaffeinated coffee and soft drinks. Avoid any processed food, artificial colors, stimulant food, canned foods, smoking, dairy products, meats, eggs, and fish. Limit your total daily fat intake to 30 percent of your total calories. Try not to consume more than 300 milligrams of cholesterol a day. Oatmeal, porridge, basil and beetroots are known to have antidepressant qualities. Regular exercise can help relieve moderate depression by triggering natural mood-enhancing chemicals.