Page 316 - Vitamin D and Cancer

13 Vitamin D and Colorectal Cancer 303

In summary, most case-control studies support an inverse association between
25-D levels and colorectal cancer. Indeed, a combined analysis of five of the stud-
3
ies listed above shows a strong statistically significant inverse correlation between
25-D and risk of colorectal cancer [40–42, 44, 45, 47]. The odds ratio for colorec-
3
tal cancer was 1, 0.82, 0.66, and 0.46 (p < 0.0001) from the lowest to the highest
trend
quartiles of 25-D . Individuals in the highest quartile had less than half the risk of
3.
colorectal cancer of those in the lowest quartile. The combined analysis projected
a 50% reduction in risk of colorectal cancer with levels of 34 ng/mL and higher.
This is consistent with recent data from the National Health and Nutrition
Examination Survey (NHANES) that support an association between a replete
vitamin D status and colorectal cancer mortality [48]. Between 1988 and 1994, the
NHANES enrolled US individuals aged 17 years and older and included non-
Hispanic whites, non-Hispanic blacks, and Mexican Americans with oversampling
from the latter two. Among all enrolled patients, 16,818 (95%) had a baseline 25-D
3
level by RIA and a known mortality status. Follow-up of this cohort continued until
the last day of the year 2000. Sixty-six patients died of colorectal cancer during the
follow-up period. An inverse association was present between 25-D levels and
3
colorectal cancer mortality (p = 0.02). Patients with 25-D levels exceeding 32 ng/
3
mL had a lower risk of colorectal cancer mortality compared to patients with levels
lower than 20 ng/mL (risk ratio = 0.28, 95% CI 0.11–0.68) [48].

13.1.2.5 Vitamin D Intake and the Risk of Colorectal Cancer

Several case–control and cohort studies have evaluated the effect of dietary vitamin D
on the risk of colorectal polyps or cancer. Garland first evaluated vitamin D intake
and risk of subsequent colorectal cancer incidence based on 28 day dietary intake
diaries completed between 1957 and 1959 in 1954 men [49]. The incidence of
colorectal cancer decreased from the lowest to the highest quartiles of vitamin D
intake [49]. Another analysis of 35,216 women on the Iowa Women’s Health Study
investigated the association between baseline dietary questionnaires and the risk of
subsequent colorectal cancer [50]. Females with the highest quintile of vitamin D
intake had a 32% lower risk of colorectal cancer compared to the lowest quintile;
this did not reach statistical significance [50]. The Health Professionals Follow-up
Study consisted of 51,529 male professionals who had provided baseline informa-
tion about dietary habits. Six year follow-up to assess colorectal cancer incidence
and death was obtained by mail (response rate 94%) [51]. A higher intake of vita-
min D was associated with a slight decrease in the risk of colorectal cancer (relative
risk [RR] = 0.88; CI: 0.54–1.42) on multivariate analysis [51]. A larger cohort was
evaluated from the Nurses’ Health Study [52]. Among study participants, 89,448
respondents to dietary questionnaires and who were free of cancer were followed
for colorectal cancer incidence. An inverse association between dietary vitamin D
intake and risk of colorectal cancer was noted. The relative risk (RR) for colorectal
cancer was 0.84 for the highest quintile of vitamin D when compared to the lowest
quintile (CI: 0.63–1.13). The relative risk reduction was more pronounced when