The reason for the association has to do with the fact that folic acid deficiency lowers brain 5-hydroxytryptamine (the brain hormone serotonin) and S-adenosylmethionine, which raises serotonin levels. There is evidence that 5-HT is decreased in depression (Br J Psychiatry, 1967; 113: 1237-64). So what probably happens is that a depressed person low in folic acid is also low in brain 5-HT
levels (Prog Neuropsychopharmacol Bio Psychiatry, 1989; 13(6): 841-63). A number of studies showed that patients improve significantly with folic acid supplements (The Lancet, 1990; 336; 392-95).
Another common deficiency in depression is B6. Again, laboratory evidence of vitamin B6 deficiency is common in depression. Of all the possible psychiatric diagnoses, patients in a psychiatric hospital who are deficient in B6 are most likely to be diagnosed with "endogenous depression" that is, inherent depression, rather than a response to an outside event (Nutr Rep In, 1983; 27 (4): 867-73; Br J Psychiatry, 1979; 135: 249-54).
Although we don't have evidence of how frequently B6 improves depression, we do know that B6 can treat depression caused by the birth control pill. The Pill not only interferes with B6, but also speeds up the destruction of tryptophan, preventing it from being converted to serotonin. (Acta Vitaminol Enzymol, 1982; 4 (1-2): 45-54).
Other B vitamin deficiencies linked to depression are those of riboflavin (vitamin B2) and thiamine (vitamin B1). In early stages of thiamine deficiency, normal people become depressed, irritable and fearful. It's also common in hospitalized mental patients (Am J Clin Nutr, 1957; 5 (2): 109-20). As for riboflavin, in one study of 172 patients in a psychiatric hospital, more than one-fourth were found to be deficient. Those patients who had a riboflavin deficiency also had been diagnosed as having a mood disorder ((Br J Psychiatry, 1982; 141: 271-72).
Vitamin B12 is the final B vitamin deficiency often linked to psychiatric problems. About 5 per cent of people admitted to a psychiatric hospital are deficient in vitamin B12, and about 10 per cent have lower than normal levels of the vitamin (Acta Med Scanda, 1965; 177: 689-99).
Vitamin C also appears to have a role in maintaining mood. One of the first symptoms of mild scurvy, the vitamin C deficiency disease, is depression, along with tiredness and irritability (Am J Clin Nutr, 1971; 24: 432-3). Although we all tend to associate scurvy with Third World countries and sailors of several centuries ago, mild scurvy in industrialized countries isn't as rare as we think. When the diets of 12 depressed women who subsequently attempted suicide were compared with those of a similar control group, the only significant difference found was a lower intake of vitamin C (J Orthomol Med, 1987; 2 (4): 217-18). There's also evidence that giving vitamin C makes a difference. In one study, 40 chronic psychiatric patients were given vitamin C or a placebo. Three weeks later, only the patients given vitamin C were less depressed (Br J Psychiatry, 1963; 109: 294-9).
Besides vitamins, a number of mineral deficiencies may bring on depression. Both too much and too little calcium in the blood may be associated with depression, an interesting factor considering the tendency to push megadoses of calcium indescriminately on postmeno-pausal women (Br J Psychiatry, 1984; 145: 477).
Although we know that people with iron-deficiency anemia feel tired and depressed, even after iron supplementation cures the anemia, the depression may not resolve for months. The exact nature of the relationship is unknown, although we do know that some areas of the brain have high iron concentrations, and it may be that a reduced level of iron in the brain brings on the depression (Anabolism, Jan-Feb, 1984).