Concern about risk of skin cancer from ultraviolet radiation should be balanced by concern about vitamin D
The following was rejected by the British Journal of Dermatology, November 29, 2012
To the Editor:
Two recent papers in the British Journal of Dermatology made recommendations on how to reduce skin cancer incidence rates in Europe.1,2 While reducing skin cancer incidence rates is a worthwhile health measure, policies aimed doing so not compromise overall health. Ultraviolet (UV) irradiance is the primary risk factor for skin cancer. However, solar UVB is also the most important source of vitamin D for most people, and vitamin D has many health benefits. Thus, measures aimed at reducing skin cancer incidence should be designed in a manner not to reduce vitamin D production from solar UVB irradiance or recommend vitamin D supplements to compensate for reduced vitamin D production from solar UVB.
Skin pigmentation changes throughout the world in response to solar UV doses, striking a balance between protection against folate destruction and the effects of free radical formation on one hand and vitamin D production on the other hand.3 Most Europeans have skin pigmentation well suited to their location due to the long history of civilization in Europe and the relative immobility compared to, say, the United States. Thus, Europeans should not be at high risk for skin cancer.
There is reasonable evidence that skin cancer is associated with better overall health outcomes, likely through higher serum 25-hydroxyvitamin D 25(OH)D concentrations. A study in Denmark found a 10-year mortality rate ratio = 0.91 (95% CI: 0.89-0.92) for those who developed basal cell carcinoma (BCC), but a higher mortality rate ratio for those who developed squamous cell carcinoma (SCC).4 Smoking is an important risk factor for SCC but only weakly for BCC,5 as well as many adverse health outcomes, which likely explains the different findings. An ecological study of internal cancer mortality rates with respect to nonmelanoma skin cancer mortality rate in Spain found inverse correlations for mortality rates for 15 types of cancer.6 A study of cancer incidence rates related to 54 categories of occupation using lip cancer standardized incidence ratios (SIRs) less lung cancer SIRs for men as the index of solar UVB dose found this index significantly inversely correlated with 14 types of internal cancer for men and three types of internal cancers for women.5 The evidence that solar UVB reduces the risk of many types of cancer is reviewed in a recent paper.7
There are many types of disease for which vitamin D is protective in addition to many types of cancer. Such diseases include Alzheimer’s disease, cardiovascular disease, diabetes mellitus, and respiratory infections.8,9 Based on calculations of disease outcomes with respect to serum 25(OH)D concentrations, it was estimated that mortality rates in Europe could be reduced by 15-17% and life expectancy increased by 2 years if population mean 25(OH)D concentrations were increased from 54 nmol/l to 110 nmol/l.8 Similar estimates were found for the United States.9 A conference of vitamin D experts meeting in Paris in 2009 recommended serum 25(OH)D concentrations above 75-100 nmol/l.10
Looking at Tables 3-5 in Ref. 1, it appears that outdoor hobbies contribute the most risk for BCC, SCC, and melanoma, followed by outdoor work for BCC and SCC, with sunburns and sunbed use contributing much less risk. However, as found for Nordic countries, outdoor work was very protective against many types of internal cancers for males. As for outdoor hobbies, the best advice would likely be to avoid sunburning, as outdoor hobbies are an important source of vitamin D. To compensate for any vitamin D production lost due to sun avoidance and protection measures, vitamin D supplements could be made more readily available and countries could consider fortifying food with vitamin D3.
1.de Vries E, Arnold M, Altsitsiadis E, et al. Potential impact of interventions resulting in reduced exposure to ultraviolet (UV) radiation (UVA and UVB) on skin cancer incidence in four European countries, 2010-2050. Br J Dermatol. 2012; 167 Suppl 2:53–62.
2. Diepgen TL, Fartasch M, Drexler H, Schmitt J. Occupational skin cancer induced by ultraviolet radiation and its prevention. Br J Dermatol. 2012; 167 Suppl 2:76–84.
3. Jablonski NG, Chaplin G. Colloquium paper: human skin pigmentation as an adaptation to UV radiation. Proc Natl Acad Sci U S A. 2010; 107 Suppl 2:8962–8.
4. Jensen AØ, Lamberg AL, Jacobsen JB, et al. Non-melanoma skin cancer and ten-year all-cause mortality: a population-based cohort study. Acta Derm Venereol. 2010; 90:362–7.
5. Grant WB. Role of solar UV irradiance and smoking in cancer as inferred from cancer incidence rates by occupation in Nordic countries. Dermatoendocrinol. 2012; 4:203–11.
6. Grant WB. An ecologic study of cancer mortality rates in Spain with respect to indices of solar UV irradiance and smoking. Int J Cancer. 2007; 120:1123–7.
7. Grant WB. Role of solar ultraviolet-B irradiance in reducing cancer risk. Anticancer Agents Med Chem. 2012 Oct 12. [Epub ahead of print]
8. Grant WB. An estimate of the global reduction in mortality rates through doubling vitamin D levels. Eur J Clin Nutr. 2011; 65:1016–26.
9. Grant WB. In defense of the sun: An estimate of changes in mortality rates in the United States if mean serum 25-hydroxyvitamin D levels were raised to 45 ng/mL by solar ultraviolet-B irradiance. Dermatoendocrinol. 2009; 1:207–14.
10. Souberbielle JC, Body JJ, Lappe JM, et al. Vitamin D and musculoskeletal health, cardiovascular disease, autoimmunity and cancer: Recommendations for clinical practice. Autoimmun Rev. 2010; 9:709-15.
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