Ola Engelsen

Calculated Ultraviolet Exposure Levels for a Healthy Vitamin D Status

Abstract The dangers of overexposure to sunlight have been well publicized, but less attention has been given to an acknowledged benefit of exposure to UV radiation; that being the cutaneous synthesis of vitamin D3. Here we define a standard vitamin D dose on the basis of recently recommended requirements for vitamin D that take account of its risk reduction role in a variety of diseases, and present a web-based tool that enables the reader to calculate associated exposure times for any time and place using either default values or user-selected conditions. Either it is not possible to synthesize vitamin D3 at high latitudes in winter, or the exposure time required to reach a standard dose is sometimes impractical. Where solar UV is sufficient, a risk-benefit analysis of sunburn vs. vitamin D3 synthesis shows that the best time for brief sun exposure is in the middle of the day. For low solar elevation angles common at high latitudes, a fine line exists between adequate UV exposure for vitamin D3 synthesis and a risk of sun burn.

Daily duration of vitamin D synthesis in human skin with relation to latitude, total ozone, altitude, ground cover, aerosols and cloud thickness.

Abstract Vitamin D production in human skin occurs only when incident UV radiation exceeds a certain threshold. From simulations of UV irradiances worldwide and throughout the year, we have studied the dependency of the extent and duration of cutaneous vitamin D production in terms of latitude, time, total ozone, clouds, aerosols, surface reflectivity and altitude. For clear atmospheric conditions, no cutaneous vitamin D production occurs at 51 degrees latitude and higher during some periods of the year. At 70 degrees latitude, vitamin D synthesis can be absent for 5 months. Clouds, aerosols and thick ozone events reduce the duration of vitamin D synthesis considerably, and can suppress vitamin D synthesis completely even at the equator. A web page allowing the computation of the duration of cutaneous vitamin D production worldwide throughout the year, for various atmospheric and surface conditions, is available on the Internet at http://zardoz.nilu.no/~olaeng/fastrt/VitD.html and http://zardoz.nilu.no/~olaeng/fastrt/VitD-ez.html. The computational methodology is outlined here.

The High Prevalence of Vitamin D Insufficiency across Australian Populations Is Only Partly Explained by Season and Latitude

Background Inadequate sun exposure and dietary vitamin D intake can result in vitamin D insufficiency. However, limited data are available on actual vitamin D status and predictors in healthy individuals in different regions and by season. Methods We compared vitamin D status [25-hydroxyvitamin D; 25(OH)D] in people < 60 years of age using data from cross-sectional studies of three regions across Australia: southeast Queensland (27°S; 167 females and 211 males), Geelong region (38°S; 561 females), and Tasmania (43°S; 432 females and 298 males). Results The prevalence of vitamin D insufficiency (≤ 50 nmol/L) in women in winter/spring was 40.5% in southeast Queensland, 37.4% in the Geelong region, and 67.3% in Tasmania. Season, simulated maximum daily duration of vitamin D synthesis, and vitamin D effective daily dose each explained around 14% of the variation in 25(OH)D. Although latitude explained only 3.9% of the variation, a decrease in average 25(OH)D of 1.0 (95% confidence interval, 0.7–1.3) nmol/L for every degree increase in latitude may be clinically relevant. In some months, we found a high insufficiency or even deficiency when sun exposure protection would be recommended on the basis of the simulated ultraviolet index. Conclusion Vitamin D insufficiency is common over a wide latitude range in Australia. Season appears to be more important than latitude, but both accounted for less than one-fifth of the variation in serum 25(OH)D levels, highlighting the importance of behavioral factors. Current sun exposure guidelines do not seem to fully prevent vitamin D insufficiency, and consideration should be given to their modification or to pursuing other means to achieve vitamin D adequacy.

Vitamin D status of middle-aged women at 65–71°N in relation to dietary intake and exposure to ultraviolet radiation

Objective: To determine the vitamin D status of middle-aged women living in the Norwegian arctic and its relationship with vitamin D intake and exposure to ultraviolet (UV) radiation. Design: Cross-sectional study. Subjects and setting: This study is based on measurements of 25-hydroxyvitamin D (25(OH)D) levels in a sub-sample of the Norwegian component of the EPIC biological bank, which consists of blood samples from a random selection of participants in the Norwegian Women and Cancer Study. From November 2001 until June 2002, 309 blood samples were collected from a total of 443 invited middle-aged women (44–59 years) in northern Norway (65–718N) (crude response rate, 69.8%). Questionnaire data provided information on dietary sources of vitamin D and UV exposure. Results: Median plasma 25(OH)D concentration for the whole group was 55.0 nmol l 21 (range 8.1–142.8 nmol l 21 ). Vitamin D intake was a significant predictor of 25(OH)D status (P ¼ 0.0003). The time of the year when the blood sample was collected significantly predicted plasma 25(OH)D level (P ¼ 0.005). Levels of 25(OH)D were positively associated (P ¼ 0.0002) with estimated hours per day of exposure to UV-B radiation. Residing in northern Norway during the summer prior to blood sampling was negatively associated with 25(OH)D concentration (P ¼ 0.001). The prevalence of moderate hypovitaminosis D was highest in January–February, when a quarter of the participants had 25(OH)D concentrations #37.5 nmol l 21 . Conclusions: Increased ingestion of marine food items that provide vitamin D should be promoted and further studies should be carried out to investigate vitamin D status in arctic populations in relation to both UV exposure and traditional food sources.

From model intercomparison toward benchmark UV spectra for six real atmospheric cases

The validity of a radiative transfer model can be checked either by comparing its results with measurements or with solutions for artificial cases. Unfortunately, neither type of comparison can guarantee that the spectral UV surface irradiance is accurately calculated for real atmospheric cases. There is a need therefore for benchmarks, i.e., standard results that can be used as a validation tool for UV radiation models. In this paper we give such benchmarks for six cloud-free situations. The chosen cases are characterized by different values of solar zenith angle, ozone column, aerosol loading, and surface albedo. Observations are also available for these cases to allow a further comparison between model results and measurements. An intercomparison of 12 numerical models is used to construct the benchmarks. Each model is supplied with identical input data, and a distinction is made between models that assume a planeparallel geometry and those that use a pseudospherical approximation. Differences remain between the model results, because of different treatments of the input data set. Calculations of direct and global transmission and direct and global irradiance are within 3% for wavelengths longer than 320 nm. For the low-Sun cases the calculations are within 10% for wavelengths longer than 300 nm. On the basis of these calculations, six benchmark UV spectra (295–400 nm) are established with a standard deviation of 2%. Relative standard deviations are higher for the lowest absolute intensities at low Sun (5% at 300 nm). The variation between models is typically less than the variation seen between model and measurement. Differences between the benchmarks and the observed spectra are mainly due to the uncertainty in the input parameters. In four of the six cases the benchmarks agree with the observed spectra within 13% over the whole UV spectral region.

Estimated equivalency of vitamin D production from natural sun exposure versus oral vitamin D supplementation across seasons at two US latitudes

BACKGROUND The relationship between oral vitamin D supplementation and cutaneous photosynthesis is not well understood. OBJECTIVE We sought to provide estimates of the equivalency of vitamin D production from natural sun exposure versus oral supplementation. METHODS Using the FastRT simulation tool, we determined sun exposure times needed to achieve serum vitamin D(3) concentrations equivalent to 400 or 1000 IU vitamin D for individuals of various Fitzpatrick skin types living in Miami, FL, and Boston, MA, during the months of January, April, July, and October. RESULTS Peak ultraviolet B irradiation for vitamin D synthesis occurs around 12 pm Eastern Standard Time (EST). In Boston, MA, from April to October at 12 pm EST an individual with type III skin, with 25.5% of the body surface area exposed, would need to spend 3 to 8 minutes in the sun to synthesize 400 IU of vitamin D. It is difficult to synthesize vitamin D during the winter in Boston, MA. For all study months in Miami, FL, an individual with type III skin would need to spend 3 to 6 minutes at 12 pm EST to synthesize 400 IU. Vitamin D synthesis occurs faster in individuals with lighter Fitzpatrick skin types. The duration to attain 1000 IU of vitamin D is longer in all scenarios. LIMITATIONS Results of the computer model are only approximations. In addition, calculations were made based on the assumption that (1/4) of 1 minimal erythema dose directed at (1/4) body surface area is equal to 1000 IU of oral vitamin D. CONCLUSIONS Although it may be tempting to recommend intentional sun exposure based on our findings, it is difficult, if not impossible to titrate ones exposure. There are well-known detrimental side effects of ultraviolet irradiation. Therefore, oral supplementation remains the safest way for increasing vitamin D status.

Antineutrophil Cytoplasmic Antibody-Associated Vasculitides: Could Geographic Patterns Be Explained by Ambient Ultraviolet Radiation?

OBJECTIVE This ecological study describes and quantifies the association between ambient ultraviolet (UV) radiation levels, including daily winter vitamin D effective UV radiation levels and the incidence of the 3 antineutrophil cytoplasmic antibody-associated vasculitides (AAVs): Wegeners granulomatosis (WG), microscopic polyangiitis (MPA), and Churg-Strauss syndrome (CSS). Latitudinal variation in occurrence of the AAVs, especially WG, has been previously reported. For other autoimmune diseases such as multiple sclerosis and type 1 diabetes mellitus, inverse associations with latitude are hypothesized to indicate a causative role for low UV radiation exposure, possibly acting via vitamin D status. METHODS Published epidemiologic studies provided data on incident cases, total population of study regions, age-specific incidence rates, and study location. From these data and online age-specific population data, we calculated crude incidence rates, the expected number of cases (to control for possible age confounding), and measures of ambient UV radiation. Negative binomial regression models were used to calculate the incidence rate ratio (IRR) for a 1,000 joules/m(2) increase in ambient UV radiation. RESULTS The incidence of WG and CSS increased with increasing latitude and decreasing ambient UV radiation, with a stronger and more consistent effect across different UV radiation measures for WG, e.g., for average daily ambient clear sky erythemal UV radiation (WG: IRR 0.64 [95% confidence interval (95% CI) 0.44-0.94], P = 0.02; CSS: IRR 0.67 [95% CI 0.43-1.05], P = 0.08; MPA: IRR 1.16 [95% CI 0.92-1.47], P = 0.22). There was no apparent latitudinal variation in MPA incidence. CONCLUSION Our findings are consistent with a protective immunomodulatory effect of ambient UV radiation on the onset of WG and CSS. We discuss possible mechanisms, including the effect of vitamin D on the immune system.

Vitamin D-effective solar UV radiation, dietary vitamin D and breast cancer risk

Vitamin D is well known for its important role in calcium and phosphor homeostasis. Recent research suggests that vitamin D also prevent some type of cancers. We studied solar vitamin D effective UV radiation (VD dose), dietary vitamin D, sun‐seeking holidays, use of solarium, frequency of sunburn and breast cancer risk in a large population‐based cohort study. A total of 41,811 women from the prospective Norwegian Women and Cancer Study, aged 40–70 years at baseline, were followed from 1997/1998 to 2007. Dietary vitamin D intake was calculated at baseline. Information on historical VD dose was used as a proxy for cutaneously obtained vitamin D status. Cox proportional hazards model was used. We adjusted for age, height, BMI, baseline menopausal status, use of hormone replacement therapy, use of oral contraception, alcohol, mothers history of breast cancer, mammography and parity. During 8.5 years of follow‐up, 948 new cases of breast cancer were registered using data from the Norwegian Cancer Registry. We found no significant associations between VD dose, or vitamin D intake, or sun‐seeking holidays, or use of solarium, or frequency of sunburn, and breast cancer risk. Relative risks (95% confidence intervals) for highest versus lowest category were 1.17 (0.95–1.44), 0.95 (0.75–1.21), 1.07 (0.87–1.32), 0.93 (0.76–1.14) and 1.10 (0.89–1.36), respectively. Our results do not support an association between vitamin D status, and breast cancer risk.

Ultraviolet exposure scenarios: risks of erythema from recommendations on cutaneous vitamin D synthesis.

Exposure to sunlight is a major source of vitamin D for most people yet public health advice focuses overwhelmingly on avoiding exposure of unprotected skin because of the risks of erythema and skin cancer. We have calculated the exposure required to gain a number of proposed oral-equivalent doses of vitamin D, as functions of latitude, season, skin type and skin area exposed, together with the associated risk of erythema, expressed in minimum erythema doses. The model results show that the current recommended daily intake of 400 IU is readily achievable through casual sun exposure in the midday lunch hour, with no risk of erythema, for all latitudes some of the year and for all the year at some (low) latitudes. At the higher proposed vitamin D dose of 1000 IU lunchtime sun exposure is still a viable route to the vitamin, but requires the commitment to expose greater areas of skin, or is effective for a shorter period of the year. The highest vitamin D requirement considered was 4000 IU per day. For much of the globe and much of the year, this is not achievable in a lunchtime hour and where it is possible large areas of skin must be exposed to prevent erythema. When the only variable considered was skin type, latitudinal and seasonal limits on adequate vitamin D production were more restrictive for skin type 5 than skin type 2.

The solar UV radiation level needed for cutaneous production of vitamin D3 in the face. A study conducted among subjects living at a high latitude (68° N)

Populations at high latitudes experience several winter months with insufficient UV solar radiation to induce a significant cutaneous production of vitamin D. This unique study was designed to pursue an in vivo threshold of UV radiation needed for cutaneous production of vitamin D to take place if only the face was exposed to UV radiation. The vitamin D status were measured by analyzing blood samples weekly from a study group of 15 subjects over a period of 2 months during late winter, when UV radiation can be expected to increase substantially from rising solar elevations. Statistical analysis showed no significant positive association between the mean UV radiation dose and the mean 25(OH)D (25-hydroxy vitamin D) for the group. On an individual basis, however, we found indications that subjects with very low initial concentration of 25(OH)D (<30 nmol l(-1)) seemed to respond to UV radiation as early as in the beginning of March. For other individuals diet seemed to be the dominant controlling factor for 25(OH)D levels.