Page 322 - Vitamin D and Cancer

13 Vitamin D and Colorectal Cancer 309

mean concentrations of 30 ng/mL or higher resulted in a reduction in parathyroid
hormone levels (PTH) and in the risk of fractures [89]. Similarly, no reduction in
colorectal cancer has been noted with 400 IU of cholecalciferol and calcium supple-
mentation [45]. However, a combined analysis of five case–control studies supports
a 50% risk reduction in patients with 25-D levels exceeding 34 ng/mL [47].
3
Furthermore, colorectal cancer related mortality has been shown to be inversely
associated with 25-D levels with significant benefits noted in the population with
3
levels exceeding 32 ng/mL compared to those <20 ng/mL [48].
These data strongly suggest that if a protective effect for vitamin D supplemen-
tation exists, it would likely be achieved with a cholecalciferol dose resulting in
25-D levels in excess of 30 ng/mL. Given that the majority of the US population
3
has 25-D concentrations below 30 ng/mL and that up to 36% of normal healthy
3
population has concentrations below 20 ng/mL [90], it becomes evident that chole-
calciferol supplementation doses considerably higher than 400 IU/day would be
needed for prevention purposes. Data from healthy volunteers receiving cholecal-
ciferol at 1,000–10,000 IU/day suggest that a dose of 1,700 IU/day is required to
achieve the optimal 32 ng/mL concentration [87]. Other data suggest the need for
a cholecalciferol dose of 4,000 IU/day to achieve an average steady state concentra-
tion of 38 ng/mL [91]. Therefore, a conservative dose of cholecalciferol of
2,000 IU/day is suggested for the goal of achieving the optimal 25-D concentra-
3
tions exceeding 30 ng/mL.
It is important to point that the current epidemiological and prospective data
support an association between low levels of 25-D and increased incidence of
3
colorectal cancer and increased colorectal mortality. This does not necessitate a
cause effect relationship between vitamin D deficiency and colorectal cancer. It is
possible that other biological factors or life style practices predispose subjects to
both colorectal cancer and vitamin D deficiency. It is therefore essential that pro-
spective randomized clinical trials with higher doses of cholecalciferol vs. placebo
are conducted to determine if vitamin D status plays a significant role in colorectal
carcinogenesis and mortality.

References

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