Page 189 - Vitamin D and Cancer

176 S.A. Mazzilli et al.

8.1 Introduction

Current epidemiological data suggest that Vitamin D may act as a chemopreventive
agent to reduce cancer incidence and mortality. The hypothesis that there is an
inverse relationship between sunlight, vitamin D and cancer was first noted in 1937
by Peller, who proposed that those exposed to more sunlight had fewer internal
cancers [1]. Following Nixon’s declaration of war on cancer in 1970, maps were
created to examine the geographical distribution of cancer mortality. It was these
maps that lead the Garlands’ to publish a study in 1980, proposing that vitamin D
and calcium protected against colon cancer [2]. This study caught the attention of
many, leading to further research into the potential preventive nature of vitamin D
against cancer.
It has been proposed that the serum 25(OH)D levels needed to obtain a pre-
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ventive effect is in the range of 30–60 ng/mL. However, a large percentage of
individuals have serum 25(OH)D levels far below that level and are thought to
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be vitamin D deficient. Vitamin D deficiencies are associated with lifestyle and
environmental factors that result in inadequate sun exposure and dietary intake of
vitamin D. The amount of vitamin D that is able to be synthesized in the skin by
UV-B exposure is determined by a number of variables including: geographic
latitude, weather, time of day, pollution and use of sun protection lotions or
sprays [3, 7]. In addition, campaigns to control sun exposure due to its association
with skin cancer may also play a role in the growing number of individuals with
low vitamin D levels [4]. In the US, dietary vitamin D is responsible for only a
small percent of serum 25(OH)D levels, as the American diet does not include
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many foods that are naturally high in vitamin D. Although many foods in the
American diet are supplemented with vitamin D, such as milk, yogurt, select
juices and bread products, the contributions are less than that of multi-vitamins
[5]. Currently the majority of multi-vitamins only contain 400 international units
(IU) of Vitamin D . This is based on the 1997 recommendations of the Food and
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Nutrition Board (FNB) at the Institute of Medicine of The National Academies
for adequate vitamin D intake [6]. However, due to changes in lifestyle that have
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resulted in reduced sun exposure it is now being suggested that daily intake rec-
ommendations be increased to ³1,000 IU [8]. Increasing the recommended daily
vitamin D intake particularly during the winter months may reduce the number of
people deficient in vitamin D [4].
Current epidemiological studies have examined the relationship between serum
25(OH)D levels and both incidence and mortality rates in cancers of the colon,
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breast, prostate, ovarian, renal and lung. A recent review by Garland et al. stated
that raising serum 25(OH)D levels to 40–60 ng/mL may prevent 58,000 new cases
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of breast cancer and 49,000 new cases of colorectal cancer, in addition to poten-
tially reducing the mortality rates of individuals with colon, breast and prostate
cancer by as much as 50% [8]. An inverse relationship between sunlight exposure
and lung cancer incidence has been proposed by Mohr et al. after examining data
from patients in 111 countries [9].