Research has shown that as many as 30% of patients hospitalized for depression are vitamin B12 deficient. One study of of 700 physically disabled women over the age of 65 found that vitamin B12 deficient women were twice as likely to be severely depressed as the non-deficient women.
Another study of 3,884 elderly men and women with depressive disorders found that those with vitamin B12 deficiency were nearly 70% more likely to experience depression than those with sufficient vitamin levels. Researchers have recommended that, due to the high prevalence of vitamin B12 deficiency in older individuals, it may be beneficial to screen for vitamin B12 deficiency as part of a medical evaluation for depression.
A number of drugs reduce the absorption of vitamin B12. For example, proton pump inhibitors (e.g. Prilosec, Prevacid), commonly used for problems like gastric reflux disease or acid reflux disease, drastically decrease stomach acid production, which is needed for the release of vitamin B12 from food (but not from supplements).
Long-term use of proton pump inhibitors has been found to decrease blood vitamin B12 levels and to contribute to bone loss. Other drugs found to inhibit vitamin B12 absorption from food include cholestyramine (a cholesterol lowering drug), chloramphenicol and neomycin (antibiotics), colchicine (anti-gout medicine), and metformin (diabetes drug). Nitrous oxide, an anesthetic, is associated with vitamin B12-deficiency, and some doctors believe vitamin B12 deficiency should be accessed prior to its use.
Vitamin B12 malabsorption and vitamin B12 deficiency are more common in adults over 50, and research has indicated that it may be related to depression, bone loss, and dementia. While a varied diet should theoretically provide enough vitamin B12 to prevent deficiency in most individuals 50 years of age and younger, individuals over the age of 50, strict vegetarians, and women planning to become pregnant should consider supplementation. Ask your doctor for a simple blood test to determine if you are B12 deficient, and if so, how much you should be taking.