Page 97 - Vitamin D and Cancer

84 E. Giovannucci

skin types I/II than III/IV. Also, men with skin types I/II experienced longer survival
after beginning hormone therapy (RR = 0.62, 95% CI = 0.40–0.95). These findings also
support that vitamin D may influence prostate cancer mortality.

4.5 Breast Cancer

4.5.1 25(OH)D Level

Two large prospective studies have examined circulating 25(OH)D levels in relation
to breast cancer risk. The first of these was the Nurses’ Health Study, which was
based on 701 breast cancer cases and 724 controls [68]. The results suggested a
moderate association; women in the highest quintile of 25(OH)D had an RR of 0.73,
95% CI = 0.49–1.07 (P trend = 0.06) when compared with women in the lowest quin-
tile of 25(OH)D. In a subgroup analysis, this inverse association was primarily in
women of ages 60 years and older, suggesting that vitamin D may be more important
for postmenopausal than for premenopausal breast cancer. Another large prospective
study of 25(OH)D level and breast cancer risk was based on the Prostate, Lung,
Colorectal, and Ovarian Cancer Screening Trial study, over which 1,005 incident
cases of breast cancer were followed from 1993 to 2005, with a mean time between
blood draw and diagnosis of 3.9 years [69]. In this cohort, women with 25(OH)D
levels in the highest quintile were not at lower risk for breast cancer when compared
to women with values in the low quintile (RR = 1.04; 95%CI = 0.75–1.45) nor was
any trend observed p(trend) = 0.81). Unlike in the Nurses’ Health Study, risk of
breast cancer was not reduced even in the stratum of older women. The range of
25(OH)D was comparable to that in the Nurses’ Health Study.
Two other small studies are noteworthy. A small nested case–control study,
based on only 28 cases, reported a nonsignificant inverse association for breast
cancer risk [25]. Also, a nested case–control study based on 96 breast cancer cases
found no association between prediagnostic 1,25(OH) D concentration and risk of
2
breast cancer, but circulating 25(OH)D was not examined in this study.

4.5.2 Vitamin D Intake

A number of studies have examined vitamin D intake in relation to breast cancer risk.
A meta-analysis for studies identified six such studies conducted up to June 2007
[70]. In the meta-analysis, vitamin D intake was not associated with risk of breast
cancer (summary RR = 0.98; 95%CI = 0.93–1.03). However, significant heterogeneity
(p < 0.01) appeared to be due to the level of vitamin D intake. When the studies were
stratified into those with vitamin D intakes higher than 400 IU or lower than this
amount, a modest association was observed only in those three studies where intakes