Arne Dahlback

Vitamin D3 from sunlight may improve the prognosis of breast-, colon- and prostate cancer (Norway)

Objective: To investigate whether prognosis of breast-, colon- and prostate cancer may be related to vitamin D3, induced from solar ultra-violet (UV) radiation, through studies on geographical and seasonal variations in UV radiation. Methods: This study includes 115,096 cases of breast-, colon- or prostate cancer, diagnosed between 1964 and 1992. Among these, 45,667 deaths due to the cancer were registered. On the basis of a north–south gradient in solar UV radiation and geographical climatic differences, Norway was divided into eight residential regions. According to seasonal variations in UV radiation, four periods of diagnosis during the year were used. Case fatality according to residential region and to season of diagnosis was estimated using Cox regression. The effects of occupational sun exposure, childbearing pattern and educational level were also evaluated. Results: No geographic variation in case fatality was observed for the three cancer types studied. A significant variation in prognosis by season of diagnosis was observed. Diagnoses during summer and fall, the seasons with the highest level of vitamin D3, revealed the lowest risk of cancer death. Conclusion: The results suggest that a high level of vitamin D3 at the time of diagnosis, and thus, during cancer treatment, may improve prognosis of the three cancer types studied.

Epidemiological support for an hypothesis for melanoma induction indicating a role for UVA radiation

Abstract. An hypothesis for melanoma induction is presented: UV radiation absorbed by melanin in melanocytes generates products that may activate the carcinogenic process. Products formed by UV absorption in the upper layers of the epidermis cannot diffuse down as far as to the melanocytes. Thus, melanin in the upper layer of the skin may be protective, while that in melanocytes may be pho‐tocarcinogenic. Observations that support this hypothesis include: (1) Africans with dark skin have a reduced risk of getting all types of skin cancer as compared with Caucasians, but the ratio of their incidence rates of cutaneous malignant melanoma to that of squamous cell carcinoma is larger than the corresponding ratio for Caucasians. (2) Albino Africans, as compared with normally pigmented Africans, seem to have a relatively small risk of getting cutaneous malignant melanomas compared to nonmela‐nomas. This is probably also true for albino and normally pigmented Caucasians. (3) Among sun‐sensitive, poorly tanning persons, frequent UV exposures are associated with increased risk of melanoma, wherease among sun‐resistant, well‐tanning persons, increased frequency of exposure is associated with decreased melanoma risk. (4) It is likely that UVA, being absorbed by melanin, might have a melanoma‐inducing effect. This is in agreement with some epidemiological investigations which indicate that sun‐screen lotions may not protect sufficiently against melanoma induction. The relative latitude gradient for UVA is much smaller than that for UVB. The same is true for the relative latitude gradient of cutaneous malignant melanoma as compared with squamous cell carcinoma and basal cell carcinoma. Under the assumption that the average slopes of the curves relating incidence rates with fluences of carcinogenic UV radiation are similar for melanomas and nonmelanomas, these facts are in agreement with the assumption that UVA plays a significant role in the induction of melano.

Addressing the health benefits and risks, involving vitamin D or skin cancer, of increased sun exposure

Solar radiation is the main cause of skin cancers. However, it also is a main source of vitamin D for humans. Because the optimal status of vitamin D protects against internal cancers and a number of other diseases, a controversy exists: Will increased sun exposure lead to net health benefits or risks? We calculated the relative yield of vitamin D photosynthesis as a function of latitude with a radiative transfer model and cylinder geometry for the human skin surface. The annual yield of vitamin D is 3.4 and 4.8 times larger below the equator than in the U.K. and Scandinavia, respectively. In populations with similar skin types, there are clear latitude gradients of all major forms of skin cancer, indicating a north–south gradient in real sun exposure. Surprisingly, the incidence rates of major internal cancers also increase from north to south. However, the survival prognosis also improves significantly from north to south. Reasons for these findings are discussed in view of the role of vitamin D. In Norway, melanoma rates increased by a factor of 6 from 1960 to 1990, while the prognosis improved in the same period. After 1990, melanoma rates have remained constant or even decreased in age groups <50 years, whereas the prognosis has not improved further. These data, together with those for internal cancers and the beneficial effects of an optimal vitamin D status, indicate that increased sun exposure may lead to improved cancer prognosis and, possibly, give more positive than adverse health effects.

Intercomparison of models representing direct shortwave radiative forcing by sulfate aerosols

The importance of aerosols as agents of climate change has recently been highlighted. However, the magnitude of aerosol forcing by scattering of shortwave radiation (direct forcing) is still very uncertain even for the relatively well characterized sulfate aerosol. A potential source of uncertainty is in the model representation of aerosol optical properties and aerosol influences on radiative transfer in the atmosphere. Although radiative transfer methods and codes have been compared in the past, these comparisons have not focused on aerosol forcing (change in net radiative flux at the top of the atmosphere). Here we report results of a project involving 12 groups using 15 models to examine radiative forcing by sulfate aerosol for a wide range of values of particle radius, aerosol optical depth, surface albedo, and solar zenith angle. Among the models that were employed were high and low spectral resolution models incorporating a variety of radiative transfer approximations as well as a line-by-line model. The normalized forcings (forcing per sulfate column burden) obtained with the several radiative transfer models were examined, and the discrepancies were characterized. All models simulate forcings of comparable amplitude and exhibit a similar dependence on input parameters. As expected for a non-light-absorbing aerosol, forcings were negative (cooling influence) except at high surface albedo combined with small solar zenith angle. The relative standard deviation of the zenith-angle-averaged normalized broadband forcing for 15 models was 8% for particle radius near the maximum in this forcing (∼0.2 μm) and at low surface albedo. Somewhat greater model-to-model discrepancies were exhibited at specific solar zenith angles. Still greater discrepancies were exhibited at small particle radii, and much greater discrepancies were exhibited at high surface albedos, at which the forcing changes sign; in these situations, however, the normalized forcing is quite small. Discrepancies among the models arise from inaccuracies in Mie calculations, differing treatment of the angular scattering phase function, differing wavelength and angular resolution, and differing treatment of multiple scattering. These results imply the need for standardized radiative transfer methods tailored to the direct aerosol forcing problem. However, the relatively small spread in these results suggests that the uncertainty in forcing arising from the treatment of radiative forcing of a well-characterized aerosol at well-specified surface albedo is smaller than some of the other sources of uncertainty in estimates of direct forcing by anthropogenic sulfate aerosols and anthropogenic aerosols generally.

Ultraviolet Radiation and Malignant Melanoma

Essential features of the epidemiology and photobiology of cutaneous malignant melanoma (CMM) in Norway were studied in comparison with data from countries at lower latitudes. Arguments for and against a relationship between ultraviolet radiation (UV) from sun and sun beds are discussed. Our data indicate that UV is a carcinogen for CMM and that intermittent exposures are notably melanomagenic. This hypothesis was supported both by latitude gradients, by time trends and by changing patterns of tumor density on different body localizations. However, even though UV radiation generates CMM, it may also have a protective action and/or an action that improves prognosis. The same may be true for a number of internal cancers. There appears to be no, or even an inverse latitude gradient for CMM arising on non-UV exposed body localizations (uveal melanoma). Furthermore, CMM prognosis was gradually improved over all years of increasing incidence (up to 1990), but during the last 10 to 15 years, incidence rates decreased and prognosis was not further improved. While CMM incidence rates are twice as high in South Norway as in North Norway, the ratios of death rates to incidence rates are higher in the North, where the annual UV fluences are lower. Death- and incidence rates in Australia and New Zealand fully support this. Comparisons of skin cancer data from Norway and Australia/New Zealand indicate that squamous cell carcinoma and basal cell carcinoma are mainly related to annual solar UVB fluences, while UVA fluences play a larger role for CMM.

Solar radiation and human health

The Sun has played a major role in the development of life on Earth. In Western culture, people are warned against Sun exposure because of its adverse effects: erythema, photoimmunosuppression, photoageing, photocarcinogenesis, cataracts and photokeratitis. However, Sun exposure is also beneficial, since moderate doses give beneficial physiological effects: vitamin D synthesis, reduction of blood pressure and mental health. Shortage of Sun exposure may be even more dangerous to human health than excessive exposure. Avoiding Sun exposure leads to vitamin D deficiency which is associated not only with rickets and osteomalacia, but also with increased risk of cardiovascular disease, multiple sclerosis, rheumatoid arthritis, diabetes, influenza, many types of cancer and adverse pregnancy outcomes. Solar radiation induces nitric oxide release in tissue and immediate pigment darkening which certainly play important roles, although these are still unknown. Action spectra relevant for health are described. We will also review what is known about spectral and intensity variations of terrestrial solar radiation as well as its penetration through the atmosphere and into human skin and tissue.

ULTRAVIOLET‐RADIATION and SKIN CANCER. EFFECT OF AN OZONE LAYER DEPLETION

The effect of changes in the ozone layer on the incidence of skin cancer was explored using data for Norway. Attempts were made to arrive at a relationship between the ‘environmental effective UV‐dose’ and the skin cancer incidence. Norway is well suited for this purpose because of the large variation in the annual UV‐dose from north to south. Furthermore we have a well developed cancer registry and a homogeneous population with regard to skin type.

The effect of clouds and surface albedo on UV irradiances at a high latitude site

At high latitudes the Earths surface is covered by snow large parts of the year. In spring the snow cover significantly increases UV radiation for cloudless as well as cloudy situations. In Tromso (69.65° N, 18.95° E), Norway, independent measurements have been made of the effective regional spectral surface albedo, the total ozone column, the effective cloud optical depth, and the surface UV irradiance. These measurements are used together with model simulations to study the effect of snow and clouds on surface erythemal radiation doses. Snow on the surface increases the monthly erythemal doses by more than 20%. Relative to cloudless sky, the clouds reduce the monthly erythemal doses by 20–40%. During snow free conditions monthly doses derived from Earth Probe/Total Ozone Mapping Spectrometer (EP-TOMS) total ozone and cloud reflectivity agree with the measurements within the experimental uncertainties. In presence of snow, however, the EP-TOMS derived data are too low by 30–40% due to snow covered surfaces being misinterpreted as clouds.

Influence of narrowband UVB phototherapy on vitamin D and folate status

Please cite this paper as: Influence of narrowband UVB phototherapy on vitamin D and folate status. Experimental Dermatology 2010; 19: e67–e72.

BIOLOGICAL UV-DOSES AND THE EFFECT OF AN OZONE LAYER DEPLETION

Abstract