A simple lack of nutrients is one of the most frequent, but least recognized, causes of depression. The most common deficiency in people with depression is a lack of one of the B vitamins, which are powerful regulators of mood. Of all vitamin deficiencies, insufficient folic acid (vitamin B9) tends to be the most frequently seen. Folic-acid deficiency lowers brain 5-HT (5-hydroxytryptamine; the brain hormone serotonin), and we know that low levels of serotonin are associated with depression.
Another common deficiency seen in depression is of vitamin B6 (pyridoxine). As this nutrient is essential for converting tryptophan to serotonin, it's no surprise that there's a strong correlation between not enough B6 and depression. Other B-vitamin deficiencies linked to depression include riboflavin (vitamin B2) and thiamine (vitamin B1). In the early stages of thiamine deficiency, normally healthy people become depressed, irritable and fearful. It's also commonly seen in hospitalized mental patients.
Vitamin B12 is yet another B-vitamin deficiency often linked to psychiatric problems. Important for the formation of red blood cells, an inadequate supply can lead to pernicious anemia, characterized by mood swings, paranoia, irritability, confusion, dementia, hallucinations or mania-symptoms that can easily be mistaken for mental illness.
Vitamin C (ascorbic acid) 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.
Besides vitamins, a number of mineral deficiencies may also bring on depression. Both too much and too little calcium in the blood may be associated with depression.
People with iron-deficiency anemia often feel tired and depressed even after supplementing with iron has cured the anemia. Furthermore, the depression may not be resolved for months. The exact nature of the relationship is as yet unknown, although what we do know is that some areas of the brain have high iron concentrations, leading some experts to speculate that a reduced level of iron in the brain may bring on depression.
Magnesium deficiency often goes hand-in-hand with calcium deficiency, and is frequently seen in depressed patients. Interestingly, the levels of magnesium in cerebrospinal fluid are especially low in patients who are suicidal.
Another potential culprit in depression is low levels of potassium, a particularly common side-effect of diuretics.