Page 100 - Vitamin D and Cancer

4 The Epidemiology of Vitamin D and Cancer Risk 87

vitamin D intake <150 IU/day (multivariate RR = 0.59; 95% CI, 0.40–0.88;
p(trend) = 0.01). Controlling for a number of other dietary and lifestyle factors did
not alter this inverse association.

4.7 Ovarian Cancer

4.7.1 25(OH)D Level

Only one report of plasma 25(OH)D in relation to risk of epithelial ovarian cancer
was identified in the literature. This study was conducted using data from three pro-
spective cohorts: the Nurses’ Health Study, the Nurses’ Health Study II, and the
Women’s Health Study [78]. The analysis was based on 224 cases and 603 controls
from the combined cohorts. The findings showed no significant association between
25(OH)D and ovarian cancer risk (top versus bottom quartile: RR = 0.83; 95% CI,
0.49–1.39; P(trend) = 0.57). However, after the first 2 years of follow-up were
excluded, an inverse association was suggested (RR = 0.67, 95%CI, 0.43–1.05). This
finding is noteworthy because ovarian cancer is often diagnosed at advanced stages,
so reverse causation may obscure the results from the early follow-up period. Another
finding was that a significant inverse association with 25(OH)D levels was observed
among overweight and obese women (RR = 0.39; 95% CI, 0.16–0.93; P(trend) = 0.04).
Finally, women with adequate versus inadequate 25(OH)D levels had a modestly
decreased risk of the subgroup of serous ovarian cancer (RR, 0.64; 95% CI, 0.39–
1.05). Though these subgroup findings are noteworthy, they require replication.

4.7.2 Sun Exposure

In the death certificate-based case–control study of ovarian cancer mortality
(n = 39,002 cases) in association with residential and occupational exposure to sun-
light described above (see section 4.3.4) [43], residential (RR = 0.84; 95% CI, 0.81–
0.88) but not occupational exposure to sunlight was inversely associated with ovarian
cancer mortality. Thus, this evidence is suggestive of a role of sunlight on ovarian
cancer risk, but of a magnitude weaker than that for colon and breast cancer.

4.8 Esophageal and Gastric Cancers

4.8.1 25(OH)D Level

Cancers of the esophagus and stomach are relatively rare in developed countries,
such as the USA, but are extremely common in some areas, particularly in Linxian,
China. One study of vitamin D, nested in a randomized trial of micronutrients [79],