Page 240 - Vitamin D and Cancer

10 Vitamin D and Prostate Cancer 227

study by Hanchette, et al. other studies have also shown the correlation between
living in areas characterized by low UV exposure and increased risk of prostate
cancer diagnosis and death due to prostate cancer [68, 69]. One study measured
exposure to UV radiation, a sunbathing score, and correlated low exposure to an
increased risk of prostate cancer with an OR 3.03 for men with the lowest quartile
of UV exposure [69]. Two recent studies have supported the hypothesis for a protec-
tive effect of sunlight [70, 71]. Two other studies done recently in Norway interest-
ingly did not find a geographic or latitude dependent increased risk of prostate
cancer mortality [72, 73] after correcting for season of diagnosis. Notably, these
studies examined a limited range of latitudes as they considered only the Norwegian
population (Table 10.3).
One possible explanation for the incomplete concordance among these studies
may be rooted in the populations that were examined. If prostate cancer indeed relies
on circulating 1,25-OH vitamin D levels for VDR signaling, these would only be
2
altered in states of relatively severe vitamin D deficiency. Normal homeostatic regula-
tory mechanisms maintain 1,25-OH vitamin D levels across a fairly broad range of
2
25-OH vitamin D concentrations. Luscombe’s study was done in the UK where there
is a high prevalence of vitamin D deficiency and therefore changes in 25-OH vitamin
D levels would have the most effect on tissue 1,25-OH vitamin D levels. Another
2
possible confounder in analyses of UV exposure is the seasonal nature of UV avail-
ability. Interestingly, several recent studies have linked the season of diagnosis and
cancer mortality [72–74]. Patients diagnosed in the summer and fall had greater sur-
vival than patients diagnosed in the winter. Zhou et al. found that patients diagnosed
and undergoing surgery for early stage lung cancer in the summer had a longer
relapse-free survival than those that were diagnosed and underwent surgery in the
winter (HR 0.33). Robsahm et al. found similar results for prostate cancer with a
summer diagnosis of prostate cancer conferring a 20–30% reduction in risk of death
when compared to other seasons of diagnosis. Recently, Lagunova et al. showed that
patients diagnosed with prostate cancer in the summer and autumn had a better prog-
nosis than those patients diagnosed in winter or spring with a relative risk of death of
0.8. This study was done in Norway where there is a relatively high prevalence of
vitamin D deficiency and the seasonal variation in UV exposure is extreme. While the
prostate cancer studies did not include measurement of vitamin D levels in the
patients, a follow-up of the Harvard School of Public Health lung cancer study did.
They reported that patients with early stage lung cancer whose vitamin D blood levels
and vitamin D intake was above the median had a significantly lower risk of recur-
rence and death when compared to patients below the median for both of these
measures (HR 0.67 and 0.64, respectively) [75].

10.5.2 Dietary Vitamin D and Calcium Intake
and Prostate Cancer Risk

Relevant studies of diet and prostate cancer risk have focused not only on
dietary intake of vitamin D, but also on calcium intake. High dietary calcium