Introduction: Mechanisms and Prevention of Environmentally Caused Cancers

Research Most (90–100%) vitamin D is produced endogenously following solar ultraviolet radiation (UVR) of precursors within sun-exposed skin (Holick 1994). Only a few foods, such as oily fish, contain significant amounts of vitamin D naturally (Holick 1994). Serum 25-hydroxyvitamin D [25(OH)D] is widely recognized as the best measure of vitamin D status (Holick 2004a), and reflects UVR exposure and vitamin D intake of the previous few months (Vieth 1999). In the absence of dietary fortification, vitamin D intake in Australia is low, varying from 1.2 to 2.6 μg/day (Nowson and Margerison 2002). This is much lower than the recommended dietary intake (5 μg/day for those 0–50 years of age, 10 μg/day for those 51–70 years, 15 μg/day for those > 70 years) (Commonwealth of Australia 2006) or the estimated intake of 10–15 μg/day required to obtain serum 25(OH)D levels of 50 nmol/L (Dawson-Hughes et al. 2005). Vitamin D status is often defined by serum levels of 25(OH)D as follows: vitamin D deficiency , 25(OH)D < 25 nmol/L; vitamin D insufficiency, 25(OH)D of 25–50 nmol/L; and optimal status, 25(OH)D > 50 nmol/L (Nowson and Margerison 2002; Vieth et al. 2001). Recent evidence suggests that the optimal serum 25(OH)D levels may be even higher, > 80 nmol/L (Dawson-Hughes et al. 2005; Hollis 2005). A balance is required in the amount of personal UVR exposure. Excessive sun exposure has been associated with increased risk of cutaneous malignant melanoma, non-melanoma skin cancers, and some cataracts (Lucas et al. 2006); however, low UVR exposure can result in vitamin D deficiency or insufficiency. It has been well established that vitamin D is essential to bone health, with low levels associated with rickets, osteoporosis, and osteomalacia (Holick 2004b). Vitamin D insufficiency causes muscle weakness and may contribute to falls in the elderly, which— when associated with osteoporosis—increases the likelihood of fractures. However, more recent evidence indicates that vitamin D insufficiency might also be associated with diseases such as colorectal cancer, prostate cancer, multiple sclerosis (MS), type 1 diabetes , cardiovascular diseases, and tuberculosis (Hughes et al. 2004; Hypponen et al. The " sun smart " public health messages, aimed at reducing skin cancer, have been successful , partly because of their simplicity. However, there is increasing awareness that any simple public health message of sun avoidance may cause harm by increasing vitamin D insufficiency (Grant et al. 2005; Sinclair 2006). A more balanced approach is now being …