Page 223 - Vitamin D and Cancer

210 F.S.G. Cheung and J.K.V. Reichardt

preventing the development of skin cancer due to the over exposure of UVR [68].
This urges careful evaluation of these current recommendations to the public.
Some parts of the population with medical conditions such as patients with
xeroderma pigmentosum who are defective in DNA repair [85] and patients receiv-
ing organ transplants that are on immunosuppressive drugs are extremely sensitive
to UVR induced skin cancer [23], and are already taking these precautions. With
the avoidance of sun exposure, it was found that patients in these two groups had
significantly lower 25(OH)D serum levels compared to controls [128, 129]. Also,
3
it was found that over 80% of veiled women had significantly low blood 25(OH)D
3
levels [60]. This problem of insufficient or even deficient in vitamin D levels were
more apparent when studies in the southern states in Australia which has relatively
low levels of sunlight, revealed that 42% of women were vitamn D insufficient and
8% of 20–59 year old women were vitamin D deficient in vitctoria. In addition, in
Hobart, up tp 10% of healthy 8 year old children were insufficient in vitamin D
[81]. Thus, inadequate vitamin D levels are a problem in all age groups.
Vitamin D status is characterized by bone health and PTH levels. This is because
increased PTH induces the expression of CYP27B1 to maintain vitamin D and in
2+
turn Ca concentrations in the blood to ensure sufficient levels are available for
bone mineralization. Vitamin D sufficiency is defined by the absence of bone dis-
ease with a PTH level of less than 65 pg/mL and a serum 25(OH)D concentration
3
of equal to or above 50 nmol/L. Vitamin insufficiency is accompanied with normal
but high bone turnover and is characterized by PTH levels less than 65 pg/mL but
can be reduced by vitamin D supplementation. Vitamin D insufficiency occurs
when serum 25(OH)D concentration is between 25 and 50 nmol/L. People with
3
vitamin deficiency have a PTH level of more than 65 pg/mL and a serum 25(OH)
D concentration of less than 25 nmol/L [116, 161]. These patients have a high bone
3
turnover, and in more severe cases with serum 25(OH)D concentration less than
3
12.5 nmol/L, osteomalacia results, where newly formed bone cannot be mineral-
ized. Osteomalacia may be asymptomatic, but the patient may also experience a
diffuse bone and muscle pain, and skeletal weakness [125]. These vitamin D status
and characteristics are summarized in Table 9.2.

Table 9.2 Indicators of vitamin D status
Serum 25(OH)D 3
Serum PTH concentration
Vitamin D status concentrations (pg/mL) (nmol/L) Characteristics
Sufficiency <65 >50 No bone disease
Insufficiency <65 but can be reduced 25–50 High but normal bone
by vitamin D turnover
supplementation
Deficiency >65 12.5–25 (moderate) High bone turnover,
<12.5 (severe) rickets or
osteomalacia