High-dose vitamin C supplement use is associated with self-reported histories of breast cancer and other illnesses in the UK Women's Cohort Study.

<bold>Objective: </bold>To determine whether frequent vitamin C supplement use is associated with healthier behaviours, and a history of cancer and other illnesses in UK women.<bold>Design: </bold>The present cross-sectional analysis examines the odds of taking supplements containing vitamin C as recorded in 4 d food diaries, based on lifestyle characteristics and morbidity history self-reported by questionnaire.<bold>Setting: </bold>A large national UK cohort study.<bold>Subjects: </bold>A total of 12,453 women aged between 37 and 79 years.<bold>Results: </bold>Women frequently taking supplements containing vitamin C, compared to those who did not, had healthier behaviours, including higher consumption of fruit and vegetables. Frequent high-dose vitamin C users (≥1000 mg) had a higher socio-economic status, visited alternative practitioners more often than family or private doctors, and were more likely to be ex-smokers and to drink little or no alcohol. Women who self-reported having had cancer (OR = 1·33, 95% CI 1·00, 1·76) or specifically breast cancer (OR = 1·70, 95% CI 1·14, 2·55), or reported a family history of cancer (OR = 1·16, 95% CI 0·95, 1·41) or breast cancer (OR = 1·26, 95% CI 1·01, 1·58) had increased odds of being frequent high-dose users after adjusting for sociodemographic and health behaviours. Women with personal or family histories of some cardiovascular or intestinal disorders were more likely to take supplements containing vitamin C, though not necessarily at high doses.<bold>Conclusions: </bold>High-dose vitamin C intake by UK women was associated with healthier behaviours and a history of breast cancer, total cancer and other illnesses. Consequences of high-dose vitamin C supplement intake are not clear at the population level. [ABSTRACT FROM AUTHOR]