Use of baseline and updated information on alcohol intake on risk for breast cancer: importance of latency.

BACKGROUND Alcohol intake has been shown to be associated with an increased risk for breast cancer. In the analysis of longitudinal prospective cohort studies, however, the analysis of repeated measurements of alcohol intake might not be straightforward. METHODS In this analysis of the Copenhagen City Heart Study, in which alcohol intake was measured four times, 9318 Danish women with no previous diagnosis of cancer were followed for breast cancer for 27 years, from 1976 to 2002. During follow-up, breast cancer was diagnosed in 476 women. RESULTS The association between alcohol intake at first measurement (baseline alcohol intake) and breast cancer was positive and approximately linear. When alcohol intake was updated during follow-up, no association was observed between breast cancer and alcohol intake. It is suggested that this difference in results may be attributable to long latency time between alcohol intake and breast cancer occurrence, because a markedly increased risk was estimated on the basis of direct lagging of risk time. CONCLUSIONS Our results support the hypothesis that baseline alcohol intake is more strongly associated with breast cancer risk than updated intake, and we suggest that this is due to the long latency between alcohol intake and breast cancer.