Page 96 - Vitamin D and Cancer

4 The Epidemiology of Vitamin D and Cancer Risk 83

97,873 prostate cancer deaths. In this study, residential exposure to sunlight had an
inverse association with prostate cancer mortality, though this association was
rather modest in magnitude (RR = 0.90; 95% CI, 0.86–0.91) [43]. Further, occupa-
tion exposure to sunlight was found not to be associated with fatal prostate cancer
risk (RR = 1.00; 95% CI, 0.96–1.05). Thus, the evidence for a link between sun
exposure and prostate cancer mortality was relatively weak, and, of note, the asso-
ciation was weaker than that observed for other cancer sites, including colon can-
cer, breast cancer, ovarian cancer, and non-Hodgkin’s lymphoma using the same
study design.
In several case–control and cohort studies, surrogates of sun exposure were
examined in relation to prostate cancer risk. One case–control study of advanced
prostate cancer is of special interest because it was based on use of a reflectometer
to measure overall sun exposure [63]. In this method, the difference between facul-
tative skin pigmentation on the forehead (a sun-exposed site) and constitutive pig-
mentation on the upper underarm (a sun-protected site) is used to estimate sun
exposure. Sun exposure estimated by reflectometry was inversely associated with
risk of advanced prostate cancer (RR = 0.51; 95% CI, 0.33–0.80). Further, this study
found that high occupational outdoor activity level was associated with a sugges-
tively reduced risk of advanced prostate cancer relative to low exposure (RR = 0.73;
95% CI, 0.48–1.11).
A cohort study was based on 5,811 non-Hispanic white men using National
Health and Nutrition Examination Survey I data; of these men, 151 (102 nonfatal,
59 fatal) were diagnosed with prostate cancer over follow-up from 1971 to 1992.
Several measures of presumed sun exposure were associated with significantly
lower risk of prostate cancer; these were longest residence in regions with high
solar radiation (RR = 0.66; 95% CI, 0.47–0.93), and high solar radiation in the state
of birth (RR = 0.49; 95% CI, 0.27–0.90) [64]. The associations were stronger for
fatal prostate cancer. Frequent recreational sun exposure in adulthood was associ-
ated with a lower risk of fatal prostate cancer only (RR = 0.47; 95% CI, 0.23–0.99).
On the basis of these findings, the authors hypothesized that both early-life and
adult exposure to sun are critical for prostate carcinogenesis, although the study did
not have adequate power to simultaneously adjust for adult and early-life
residences.
Studies in the UK are of especial interest given the low sun exposure in that region.
Several case–control studies in the UK reported on factors such as childhood sunburns,
holidays in a hot climate, and skin type in relation to prostate cancer risk. Rather
striking findings were found in subgroups characterized by childhood sunburns, holi-
days in a hot climate, and skin type; specifically, a significant 13-fold higher risk of
prostate cancer was observed in men with combinations of high sun exposure/light
skin compared to low sun exposure/darker skin type [65, 66]. Furthermore, self-
reported UV exposure parameters and skin type in 553 men with prostate cancer were
studied in association with stage, Gleason score, and survival after starting hormone
manipulation therapy [67]. UV exposures 10, 20, and 30 years before diagnosis were
inversely associated with stage, and the RR for UV exposure 10 years before diagnosis
was lowest (RR = 0.69, 95% CI = 0.56–0.86). RRs were lower in men with (lighter)