Markers of Vitamin D Intake and Risk of Breast Cancer in a California Population

Abstract

Because of the distinctive geographic pattern of breast cancer, which generally increases with increasing latitude and consequently decreasing ultraviolet B light, it was proposed that vitamin D may alter breast cancer risk [1, 2]. The geographic pattern of breast cancer incidence and mortality [1, 2] was noted to be strikingly similar to that of colon cancer, for which dietary intake of vitamin D has been reported to be protective. A study of serum levels of 25-hydroxyvitamin D concentrations showed an inverse association with colon cancer incidence [3]. Animal studies have supported a possible protective effect of dietary vitamin D in mammary tumor development [4]. Milk is fortified with vitamin D in the United States, although it it has not been fortified in Europe, except in some northern countries. A case-control study in an area with some vitamin D added to milk found that consumption of 3 or more 8-oz. glasses a day of milk was associated with a 23 per cent reduction in risk of breast cancer [5]. These lines of evidence led to this prospective study which examined the association of milk consumption, the primary source of dietary vitamin D in the U. S. diet, and breast cancer incidence. The study was performed in a cohort of elderly women who were followed for 16 years in Rancho Bernardo, California, USA.