Mood disturbances can result from a variety of causes such as tension, stress, traumatic events, chemical imbalances, thyroid disorders, nutritional deficiencies, poor diet, lack of exercise, serious medical conditions, and food allergies. Brain chemicals called neurotransmitters help regulate our behavior. Serotonin in particular, plays an important role in mood, sleep, and appetite. Low levels of serotonin are associated with anxiety, depression, and sleep disturbances. Fortunately, there are many nutrients that can be of benefit.