Vitamin B12

Several studies have shown low levels of vitamin B₁₂ in HIV-positive people.^1,2 It is unclear whether low vitamin B₁₂ levels influence HIV disease progression, or whether they are merely a consequence of disease progression. An 18 month study of HIV-positive people found that the onset of low serum vitamin B₁₂ levels was associated with CD4 cell count decline, and that normalisation of vitamin B₁₂ levels was associated with an improvement in CD4 cell count.³ Another study, which followed 310 men for 9 years, found that low serum vitamin B₁₂ levels at entry to the study were associated with an 89% increased risk of progression for AIDS after controlling for disease stage, antiretroviral therapy, alcohol intake and age.⁴

Depletion in body tissues may begin to occur at least a year before blood levels become abnormally low. Vitamin B₁₂ is thought by some doctors to protect against nerve damage and neurological disorders.

Injected supplementation has been tested in HIV-positive people and appears to improve mental functioning.⁵ Another study also showed that vitamin B₁₂ supplementation for at least six months improved mental functioning in HIV-positive people who had been deficient; an untreated control group did not show improvement.³

Peripheral neuropathy, a symptom sometimes seen in HIV-positive people and often related to the use of drugs such as ddI (didanosine, Videx / VidexEC) and ddC (zalcitabine, Hivid), can be caused by vitamin B₁₂ deficiency, so this should always be ruled out before assuming that the neuropathy is HIV-related. As yet there is no evidence that prophylactic treatment with vitamin B₁₂ will reduce the likelihood that neuropathy will develop in those receiving ddI or ddC.

It has been suggested that vitamin B₁₂ supplementation may reduce the risk of neutropenia and anaemia resulting from AZT (zidovudine, Retrovir) use. Vitamin B₁₂ is used in the production of thymidine phosphate, necessary both to break down AZT in the blood and to create red blood cells. Unless enough of this vitamin is present, AZT competes with red blood cells for available thymidine triphosphate. People who are already deficient in vitamin B₁₂ when they begin AZT therapy may be more vulnerable to anaemia and neutropenia.⁶ However, one study showed that vitamin B₁₂ supplementation does not reduce AZT toxicities once therapy has begun.⁷

Absorption of vitamin B₁₂ in HIV-positive people with gastrointestinal problems is poor unless the vitamin is injected or taken in a form that will dissolve in the mouth and be absorbed across the mucous membranes, according to some nutritionists. This vitamin treatment is available on National Health Service prescription for dietary deficiency.

All the B vitamins operate in combination, and also act in conjunction with other vitamins and minerals, so vitamin B₁₂ is best taken alongside a B-complex formula. Good food sources are fish, dairy products, kidneys, liver, eggs, beef and pork. Vegans' diets are especially likely to lack vitamin B₁₂.⁸

Vitamin B₁₂ is also known as cobalamin.