Re: The influence of health and lifestyle characteristics on the relation of serum 25-hydroxyvitamin D with risk of colorectal and breast cancer in postmenopausal women

摘要

A recent paper (1) found that the serum 25-hydroxyvitamin D (25(OH)D) concentration at the time of enrollment in the Women's Health Initiative was inversely correlated with invasive colorectal cancer for all models but only for the unadjusted models for breast cancer.Overlooked in the paper was any discussion of the role of follow-up time on the results. Another recent paper (2) showed that, for follow-up times longer than 3 years, no nested case-control study had found an inverse correlation between the prediagnostic serum 25(OH)D concentration and incidence of breast cancer. The regression fit to the data for relative risk went from 0.6 at 0 years for case-control studies to 0.95 at 7 years. However, for colorectal cancer, significant inverse correlations were found for follow-up times out to 12 years, although the regression fit went from relative risk = 0.4 at 5 years to 0.7 at 14 years. The changes in relative risk were 0.05/year for breast cancer and 0.033/year for colorectal cancer. Thus, the fact that the vitamin D effect is stronger for colorectal cancer than for breast cancer seems to be why it is easier to find a significant effect for longer follow-up periods.