Genital human papillomavirus (HPV) infection is the major causal factor of cervical intraepithelial neoplasia (CIN). The potential role of nutrition as an additional, independent risk factor for CIN has not been appropriately addressed in the context of HPV. This case-control study evaluated the etiologic role of HPV in terms of viral type and load and examined the association between CIN and plasma levels of micronutrients adjusting for HPV. Cases (n = 378) with histo-pathologically confirmed CIN and controls (n = 366) with no history of abnormal Pap smears were recruited from colposcopy and gynecology clinics, respectively. Risk of CIN was significantly increased among women who were infected with multiple HPV types (odds ratio [OR] = 21.06), a high viral load (OR = 13.08) and HPV 16 (OR = 62.49). After adjusting for HPV positivity and demographic factors, there was an inverse correlation between plasma alpha-tocopherol and risk of CIN (OR = 0.15). Plasma ascorbic acid was protective at a high level of > or = 0.803 mg/dl (OR = 0.46). CIN was not associated with plasma retinol and beta-carotene levels. The effect of genital HPV infection on CIN development is highly influenced by oncogenic viral type and high viral load. Vitamins C and E may play an independent protective role in development of CIN that needs to be confirmed in prospective studies.