Although there are many reasons for depression, some are simply a biological deficiency Most of this will be caused by the B vitamins. I will skim over the function or deficient causing depression, or a simple feeling of dread!
Ref. About.com
Vitamin B1 (thiamine): The brain uses this vitamin to help convert glucose, or blood sugar, into fuel, lacking it the brain rapidly runs out of energy. This can lead to fatigue, depression, irritability, anxiety, and even thoughts of suicide
Vitamin B3 (niacin): Pellagra-which produces psychosis and dementia, among other symptoms-was eventually found to be caused by niacin deficiency. Many commercial food products now contain niacin, and pellagra has virtually disappeared.
Vitamin B5 (pantothenic acid): Symptoms of deficiency are fatigue, chronic stress, and depression. Vitamin B5 is needed for hormone formation and the uptake of amino acids and the brain chemical acetylcholine, which combine to prevent certain types of depression.
Vitamin B6 (pyridoxine): This vitamin aids in the processing of amino acids, which are the building blocks of all proteins and some hormones. It is needed in the manufacture of serotonin, melatonin and dopamine. Vitamin B6 deficiencies, although very rare, cause impaired immunity, skin lesions, and mental confusion. A marginal deficiency sometimes occurs in alcoholics, patients with kidney failure, and women using oral contraceptives. MAOIs, ironically, may also lead to a shortage of this vitamin. Many nutritionally oriented doctors believe that most diets do not provide optimal amounts of this vitamin
Vitamin B12: Because vitamin B12 is important to red blood cell formation, deficiency leads to an oxygen-transport problem known as pernicious anemia. This disorder can cause mood swings, paranoia, irritability, confusion, dementia, hallucinations, or mania, eventually followed by appetite loss, dizziness, weakness, shortage of breath, heart palpitations, diarrhea, and tingling sensations in the extremities. Deficiencies take a long time to develop, since the body stores a three- to five-year supply in the liver. When shortages do occur, they are often due to a lack of intrinsic factor, an enzyme that allows vitamin B12 to be absorbed in the intestinal tract. Since intrinsic factor diminishes with age, older people are more prone to B12 deficiencies.
Folic acid: This B vitamin is needed for DNA synthesis. It is also necessary for the production of SAM (S-adenosyl methionine). Poor dietary habits contribute to folic acid deficiencies, as do illness, alcoholism, and various drugs, including aspirin, birth control pills, barbiturates, and anticonvulsants. It is usually administered along with vitamin B12, since a B12 deficiency can mask a folic acid deficiency. Pregnant women are often advised to take this vitamin to prevent neural tube defects in the developing fetus.
