The amino acid tyrosine functions as a biochemical precursor for the neurotransmitters norepinephrine and dopamine. These two neurotransmitting substances are active in regulating mood and other nervous system actions. Tyrosine is synthesized in the body and is not required in the diet - it is therefore considered to be a non-essential amino acid. An important function of the amino acid tyrosine is in the elevation of mood, a deficiency of norepinephrine in the brain can come about due to a lack of sufficient amounts of tyrosine - this situation can give rise to depression in the person. Body fat is also minimized by tyrosine, at the same time, excessive appetite is also suppressed by tyrosine. The production of the pigment melanin - responsible for skin and hair color - in mammals is also dependent on the presence of tyrosine. Tyrosine also has important functions in regulating the working of the adrenal, the thyroid and the pituitary glands. Tyrosine is also important in the body as it plays a role in the metabolism of the amino acid phenylalanine. Active thyroid hormones are formed by the attachment of tyrosine to iodine atoms - thus thyroid hormone synthesis is dependent on the levels of tyrosine in the body. This relationship between tyrosine and the thyroid hormone production can be gauged by the fact that low plasma levels of the amino acid tyrosine is evident during hypothyroidism - a disorder characterized by extremely low levels of thyroid hormones in the body. The physical symptoms of a deficiency of tyrosine often also include very low blood pressure, extremely low body temperature - like persistently cold hands and feet, as well as symptoms like restless leg syndrome - though different patients may experience different symptoms at varying intensities. Stress relief can also be gained by consuming supplemental L-tyrosine especially if the problem is chronic in nature. Supplements of tyrosine may be effective against disorders such as chronic fatigue and narcolepsy as suggested by the results of some studies. Supplemental L-tyrosine is suggested to alleviate the suffering of patients affected by long term anxiety, clinical depression, various allergies and persistent headaches. Such supplements may also be very beneficial to people who are experiencing a physical withdrawal from the long term use of certain drugs and medications. Supplementation might possibly aid in relieving the symptoms of Parkinson's disease and delay its effects. Good dietary sources of the amino acid tyrosine can include vegetable sources such as nuts like almonds, fruits like avocados, and bananas, all dairy products, poultry and meats, fish, oats, lima beans and pumpkin seeds as well as sesame seeds and sesame oil. The synthesis of tyrosine occurs using the amino acid phenylalanine already in the body as the precursor molecule. The time to consume supplemental L-tyrosine is at bedtime, it may also be consumed along with a meal high in carbohydrates - this ensures that tyrosine does not compete for rapid absorption and assimilation into the body with the other amino acids contained in protein rich foods. Supplements of L-tyrosine must not be used by people on a prescription of monoamine oxidase (MAO) inhibitors; such compounds are normally used to treat clinical depression. All persons being treated for clinical depression using such compounds must avoid using L-tyrosine supplements or severely limit their consumption of all foods that contain tyrosine not doing so may induce a sudden and very dangerous rise in the blood pressure of the person. A physician must be consulted on possible dietary restrictions by anyone who is using prescription medication for treating depression - diets should avoid all foods rich in tyrosine. A low level of tyrosine is also evident in people affected by the genetic disorder called phenylketonuria (PKU). People born with this condition are not able to fully metabolize the amino acid phenylalanine as the normal biochemical pathway is lacking. This leads to an accumulation of the amino acid phenylalanine in the body, a situation that can induce mental retardation and other severe disabilities in the person - treatment is usually done by a severe dietary restriction of phenylalanine rich foods. Side effects can be prevented by extreme restriction of the intake of phenylalanine - many people with PKU then tends to have very low tyrosine levels. While the evidence is contradictory, the use of tyrosine supplements might possibly benefit some people with PKU. A deficiency of the amino acid tyrosine is evident in some people affected by PKU. People affected by clinical depression may also suffer from low levels of tyrosine in the body at all times. A deficiency in all amino acids including tyrosine can be a symptom of any person who is losing very large amounts of protein - like some patients with kidney diseases often are, supplements may be required to make up for the loss in such cases.