Reference values for alpha-tocopherol and beta-carotene in the Whitehall II study

Plasma alpha-tocopherol, beta-carotene, serum lipids and their derived ratios were determined in British Civil Servants (n = 7177) at the second medical examination of the Whitehall II Study, a longitudinal study of cardiovascular disease. For plasma alpha-tocopherol the non-parametric 95% reference interval (90% confidence limits) for the total population was: 11.1 (10.9-11.3) - 51.5 (50.6-52.7) mu mol/l. For plasma beta-carotene the nonparametric reference interval for the total population was: 0.05 (0.05-0.05) - 2.14 (2.08-2.21) mu mol/l. The latter interval was wider than those previously published with a higher mean (0.61 mu mol/l) and median (0.75 mu mol/l). Plasma beta-carotene concentrations were higher in women than men with age-adjusted means of 0.70 and 0.57 mu mol/l respectively (p < 0.001). This may reflect differences in diet, lifestyle and metabolism between the sexes. The alpha-tocopherol/cholesterol ratio, as in other surveys, did not vary with age. Among men, current- and ex-smokers had a higher alpha-tocopherol/cholesterol ratio than never-smokers with age-adjusted means of 4.18, 4.19 mu mol/mmol and 4.05 mu mol/mmol respectively. This difference is as yet unexplained. Follow-up of these subjects will help to clarify the role of antioxidant nutrients as protective factors for cardiovascular disease and cancer.