General supplement use, subsequent use and cancer risk in the UK Women's Cohort Study

To determine whether general dietary supplement use is associated with cancer risk in UK women and to estimate risks related to use at one and two recording points.

Cox's proportional hazard regression models were used to estimate cancer risks for 32 665 middle-aged women in the UK Women's Cohort Study relating to any current supplement use recorded in a baseline questionnaire. During a median follow-up of 15 years, there were 3936 registered cancer incidences, including 1344 breast, 429 smoking-related and 362 colorectal cancers. Cancer risks for 12 948 of these women, who also completed questionnaires on average 4.4 years later, were estimated in relation to any supplement use at both time points (1527 cancers, including 561 breast, 131 smoking-related and 141 colorectal cancers). Adjustments were made for baseline confounders.

Total smoking-related cancers were associated with baseline supplement use (hazard ratio (HR)=1.41, 95% confidence interval (CI): 1.10, 1.81) compared with non-use, but not associated with use at both recording points (HR=1.29; 95% CI: 0.78, 2.13) compared with use at neither. There was no evidence of the associations between total, colorectal or breast cancers and baseline supplement use, or use at both recording points. In sub-analyses, no significant associations with breast cancer were found for premenopausal or postmenopausal baseline users, or similarly for use at both points (HR=1.35, 95% CI: 0.91, 2.01; and HR=0.93, 95% CI: 0.68, 1.26, respectively).

There was evidence that general supplement use was associated with increased smoking-related cancer risk, but there was no evidence of associations with total, colorectal and breast cancers.