Vitamin D in health and disease: Current perspectives
The whole thing is there as a pdf. Here is part of the conclusion
Although recommendations of daily vitamin D intake have been provided, higher levels are required in order to have real preventive or treatment effect as numerous studies have proved. UVB radiation plays an alternative ways in improving vitamin D content other than oral supplementation. Its advantage is that it will not cause vitamin D intoxication since excessive vitamin D will be broken down by UVB. However, a number of factors of the UVB such as wavelength, duration of exposure are needed to be carefully controlled so as to avoid erythema.
Despite the close link of vitamin D with human health, vitamin D inadequacy is not widely recognized as a problem by physicians and patients. Greater awareness of this problem is required among researchers, clinician, and patients of the high prevalence of vitamin D inadequacy.