Page 105 - Vitamin D and Cancer

92 E. Giovannucci

found no or relatively weak nonsignificant associations, and vitamin D intake
studies, while sparse, are not supportive of any protection for prostate cancer. In
contrast to these findings, studies generally support that more sun exposure is asso-
ciated with a lower risk of prostate cancer. Two factors are important to consider
for prostate cancer. First, most of the evidence to date has focused on incident can-
cer, while for prostate cancer the association with vitamin D may be stronger for
progression and mortality. Second, it has been observed that prostate cancer cells
lose 1-alpha-hydroxylase activity early in the carcinogenesis process [89, 90]. This
fact may suggest that prostate cancers are insensitive to the effects of circulating
25(OH)D or are only sensitive to it at very early stage decades before the diagnosis.
Thus, future studies should focus on studying vitamin D level early in life and on
risk of fatal prostate cancer.
For other cancer sites, the data are generally too sparse to support strong conclu-
sions. Some noteworthy findings bear acknowledgement. A study of predicted
25(OH)D in men found associations, particularly for mortality, largely with cancers
along the gastro-intestinal tract. This result is interesting especially given that a
similar pattern has been observed from some ecologic studies based on region of
residence. Gastrointestinal cancers account from one-quarter to one-third of all
cancer deaths across different countries, so confirming or refuting this finding is
important. In contrast, in some special high-risk populations, circulating 25(OH)D
was associated with an increased risk of pancreatic, gastric, and esophageal can-
cers. This puzzling finding could relate to different etiologies of cancer across
populations. In particular, the study of esophageal and gastric cancers was con-
ducted in a very high-risk region in China; no studies have been conducted in
regions with traditional risk factors for esophageal cancer. Other cancers that
deserve further study in particular are ovarian cancer and NHL.
Few studies have examined the potential influence of vitamin D on cancer mor-
tality or survival from cancer. Some preliminary evidence has suggested that vita-
min D status (estimated by season of diagnosis [91] or by blood sample directly
[92, 93] around the time of diagnosis) may influence survival from cancer. Also
noteworthy is that vitamin D status has been sometimes found to be more strongly
related to cancer mortality than cancer incidence. These findings suggest that
vitamin D may affect progression of cancer, or prognosis, in addition to incidence.
Intervention studies could relatively feasible test the hypothesis that administering
vitamin D after diagnosis improves survival.

References

1. Peller S, Stephenson CS (1937) Skin irritation and cancer in the United States Navy. Am
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2. Apperly FL (1941) The relation of solar radiation to cancer mortality in North American.
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3. Garland CF, Garland FC (1980) Do sunlight and vitamin D reduce the likelihood of colon
cancer? Int J Epidemiol 9:227–231