Page 224 - Vitamin D and Cancer

9 Molecular Biology of Vitamin D Metabolism and Skin Cancer 211

Knowing the consequences of vitamin D inadequacy, key parties in Australia
involved in skin cancer control have decided to provide more updated guidelines to
the puiblic regarding the importance of UVR in vitamin D synthesis [143]. Apart
from reminding people of the harmful effects of UVR on skin cancer, the new mes-
sage to the public stepped away from the idea of needing protection against the sun
at all times and stressed the importance of maintaining adequate vitamin D levels by
encouraging outdoor activities (Cancer Council Australia, 2007). However, appro-
priate precautions needs to be taken during outdoor activities For incidental sun
exposure of less than 10 min, the application of sunscreen may not be necessary, but
sunscreen application is recommended if periods of sun exposure sufficient to pro-
duce erythema (redness) are intended [116]. Although it has been found that the use
of sunscreen can have a negative effect on vitamin D synthesis [105], other clinical
studies on long term use of sunscreens showed that normal vitamin D levels can still
be maintained [102, 145]. The use of sunscreen is also encouraged by the fact that
once previtamin and vitamin D has been formed, further exposure to sunlight will
3
cause their degradation into inert over irradiation products [66] and this further UVR
exposure will only lead to increases in DNA damage. Based on this, it has been
pragmatically decided that exposure of hands, face and arms to a third to a half of a
minimum erythemal dose for 5–15 min four to six times a week with the dark
skinned and elderly population needing the greatest exposure of these recommended
values [68, 116]. However, if sun exposure is limited by medical or cultural reasons,
a tailored vitamin D supplementation plan may be necessary [143].
Currently, there are still no recommended dietary intake levels in place in
Australia but the daily vitamin D intake recommended by the Food and Nutrition
Board of the US Institute are 200 IU, 400 IU and 600–800 IU for ages 0–50 years,
51–70 years and 71+ years respectively [50]. Yet, these recommended values have
been challenged by the findings that 200 IU/day has no effect on bone status and
the recommendation of 1,000 IU has been suggested to adequately prevent bone
disease, fractures and possibly protect against some cancers [159]. Moreover, it has
even been reported that 800 IU/day supplemented vitamin D did not reduce osteo-
porotic fractures in some vitamin D replete individuals [135].
In conclusion, much research is needed to further understand the health benefits
that accompanying sun exposure. More importantly, it is essential to further eluci-
date the molecular mechanisms underlying the actions of vitamin D in preventing
classical diseases relating to bone health as well as non classical diseases such as
cancer. Such investigations should take into consideration not only different age
and racial groups, but also their health status including genetical variations in key
vitamin D metabolizing genes (Fig. 9.3). The findings in these future studies will
yield invaluable knowledge to aid appropriate recommendations for sun exposure
and vitamin D intake. These sun exposure levels will also have to take into account
of keeping the fine balance between UV exposure derived health benefits and pre-
venting skin cancer. Ultimately, this knowledge can be translated into the develop-
ment of improved vitamin D analogs to efficiently treat vitamin D related diseases
with minimal side effects.