Vitamin C status and blood pressure

Objective To examine the cross-sectional relationship between blood pressure and plasma vitamin C. Design A cross-sectional analysis. Setting A population-based study. Subjects The subjects were 835 men and 1025 women aged 45–75 years registered with general practices in Norfolk. Interventions Completion of health and lifestyle questionnaire and attendance for a health check. Main outcome measures Diastolic blood pressure (DBP), systolic blood pressure (SBP) and plasma vitamin C level. Results The mean SBP was 135.8±18.5 mmHg (mean±SD) and the mean DBP was 82.5±11.3 mmHg. The mean plasma vitamin C level was 52.6±19.7 μmol/l. The plasma vitamin C level was negatively correlated both with SBP and with DBP. These correlations persisted after adjustment for age, sex and body mass index. Adjusting for other confounders including cigarette smoking, physical activity and alcohol intake did not alter the observed association. Exclusion of subjects taking vitamin supplements and those with known hypertension did not affect the results. The differences in SBP and in DBP for a 50 μmol/l difference in vitamin C, estimated using linear regression, were −3.6 and −2.6 mmHg, respectively. Conclusions The plasma vitamin C level may be a marker of other factors; nevertheless, these results are consistent with other published work indicating that a high intake of vitamin C from food confers protection against raised blood pressure and strokes.