Plasma Vitamin B12 Level as a Potential Cofactor in Studies of Human Immunodeficiency Virus Type 1—Related Cognitive Changes

• Studies of cognitive function in subjects with human immunodeficiency virus type 1 (HIV-1) infection who remain relatively asymptomatic (ie, Centers for Disease Control stages II and III) have provided widely variable estimates of cognitive impairment. In view of the finding that approximately 25% of asymptomatic HIV-1—infected subjects demonstrate either marginal or overt vitamin B₁₂ deficiency, we have investigated plasma vitamin B₁₂ status as a potential cofactor in studies of HIV-1—related cognitive impairment. When cognition was assessed in asymptomatic (Centers for Disease Control stages II and III) HIV-1—infected participants taking into consideration vitamin B₁₂ status, those subjects with low plasma vitamin B₁₂ levels (<180 pmol/L) performed more poorly than did those with normal (≥180 pmol/L) vitamin B₁₂ status on specific measures of information processing speed and visuospatial problem-solving skills. These findings suggest that concurrent vitamin B12 deficiency may be a cofactor in subtle cognitive changes observed in the asymptomatic stages of HIV-1 infection. These differences in prevalence of low plasma vitamin B₁₂ levels may help to explain differences among studies in the proportion of HIV-1—infected subjects showing cognitive impairment.