Enhancing the production of physiologically active vitamin D3 by engineering the hydroxylase CYP105A1 and the electron transport chain.

In this study, the conversion of vitamin D3 (VD3) to its two active forms 25(OH)VD3 and 1α, 25(OH)2VD3 was carried out by engineering the hydroxylase CYP105A1 and its redox partners Fdx and Fdr. CYP105A1 and Fdx-Fdr were respectively expressed in E. coli BL21(DE3) and purified. The electron transport chain Fdx-Fdr had higher selectivity for the coenzyme NADH than NADPH. HPLC analysis showed that CYP105A1 could hydroxylate the C25 and C1α sites of VD3 and convert VD3 to its active forms. Finally, a one-bacterium-multi-enzyme system was constructed and used in whole-cell catalytic experiments. The results indicated that 2.491 mg/L of 25(OH)VD3 and 0.698 mg/L of 1α, 25(OH)2VD3 were successfully produced under the condition of 1.0% co-solvent DMSO, 1 mM coenzyme NADH and 35 g/L biocatalyst loading. This study contributes to a basis for the industrial production of active VD3 in future.

Chemical Synthesis of Side-Chain-Hydroxylated Vitamin D3 Derivatives and Their Metabolism by CYP27B1.

1α,25-Dihydroxyvitamin D3 (abbreviated here as 1,25D3 ) is a hormonally active form of vitamin D3 (D3 ), and is produced from D3 by CYP27 A1-mediated hydroxylation at C25, followed by CYP27B1-mediated hydroxylation at C1. Further hydroxylation of 25D3 and 1,25D3 occurs at C23, C24 and C26 to generate corresponding metabolites, except for 1,25R,26D3 . Since the capability of CYP27B1 to hydroxylate C1 of side-chain-hydroxylated metabolites other than 23S,25D3 and 24R,25D3 has not been examined, we have here explored the role of CYP27B1 in the C1 hydroxylation of a series of side-chain-hydroxylated D3 derivatives. We found that CYP27B1 hydroxylates the R diastereomers of 24,25D3 and 25,26D3 more effectively than the S diastereomers, but shows almost no activity towards either diastereomer of 23,25D3 . This is the first report to show that CYP27B1 metabolizes 25,26D3 to the corresponding 1α-hydroxylated derivative, 1,25,26D3 . It will be interesting to examine the physiological relevance of this finding.

Is the natural UV zone important for successful captive propagation of the Panther Chameleon (Furcifer pardalis); are different UVB irradiance exposures that generate a similar dose equally successful?

While we generally understand the optimal ultraviolet B (UVB) environment for the growth and reproduction of female Panther Chameleons Furcifer pardalis, we do not know the relative importance of UVB irradiance and dose for optimal husbandry outcomes. Accordingly, we experimented with Panther Chameleon females to test the hypothesis that UVB dose (irradiance × exposure duration) determines the outcome, regardless of the combination of UVB irradiance and exposure duration generating the dose. We varied UVB irradiance and exposure duration across treatment groups while keeping dose similar and within a range previously documented to result in reproductive success. The growth rate, age of maturity, and measurable vitamin D status were not significantly different among the treatment groups. Individuals in all groups produced viable eggs that successfully hatched. Thus, we found some support for the hypothesis that the UVB dose determines the outcome regardless of UVB irradiance. However, mean egg vitamin D3 concentration and percent hatching were higher in the highest UVB irradiance group, despite similar doses among the three groups. Preliminary field data reveal that this species occupies UV irradiance Zone 4 in Madagascar, the highest zone for reptiles recorded. Only the irradiance of the high UVB irradiance group in our experiment approached this zone and resulted in the best reproductive success. Biosynthesis of vitamin D3 and provisioning to eggs is more efficient when exposure to UVB irradiance is similar to that in their natural environment. Establishing an optimal UVB environment, based on knowledge of the natural UVB environment, is important for the propagation of Panther Chameleons in captivity.

The nocturnal leopard gecko (Eublepharis macularius) uses UVb radiation for vitamin D3 synthesis.

Vitamin D is an important regulator of calcium and phosphorus homeostasis in animals. It can be acquired from the diet or synthesised de novo when skin is exposed to UVb. Vitamin D deficiency can lead to a complex of diseases collectively called metabolic bone disease (MBD). Diurnal lizards without access to UVb are prone to develop vitamin D deficiency, even when dietary vitamin D3 is provided. A trial was conducted to determine whether juvenile nocturnal lizards require access to UVb to prevent vitamin D deficiency. All leopard geckos (Eublepharis macularius) were supplemented with dietary vitamin D3. One group was exposed to low level UVb radiation (33-51 µW/cm2) from hatching until 6 months of age and a second group remained unexposed. Animals were fed ad libitum and their growth and weight gain compared with non-exposed controls. At the end of the trial, blood samples were analysed for vitamin D3 metabolites. The concentration of the vitamin D3 metabolite, 25(OH)D3, was higher in UVb exposed animals (61 ± 20 vs. 38 ± 8 nmol/L), confirming cutaneous synthesis with UVb exposure. Growth and weight gain were similar in both groups, and this, together with the absence of clinical symptoms, suggests that dietary vitamin D3 alone can meet the vitamin D requirements for growth of this nocturnal gecko, during the first six months of life. It remains to be investigated whether the higher vitamin D metabolite levels holds other health benefits for this species, such as improved bone density or immune response.

Skin colour and vitamin D: An update.

Homo sapiens evolved in East Africa and had dark skin, hair, and eyes, in order to protect against deleterious consequences of intensive UV radiation at equatorial latitudes. Intensive skin pigmentation was thought to bear the risk of inefficient vitamin D3 synthesis in the skin. This initiated the hypothesis that within the past 75 000 years, in which humans migrated to higher latitudes in Asia and Europe, the need for vitamin D3 synthesis served as an evolutionary driver for skin lightening. In this review, we summarize the recent archeogenomic reconstruction of population admixture in Europe and demonstrate that skin lightening happened as late as 5000 years ago through immigration of lighter pigmented populations from western Anatolia and the Russian steppe but not primarily via evolutionary pressure for vitamin D3 synthesis. We show that variations in genes encoding for proteins being responsible for the transport, metabolism and signalling of vitamin D provide alternative mechanisms of adaptation to a life in northern latitudes without suffering from consequences of vitamin D deficiency. This includes hypotheses explaining differences in the vitamin D status and response index of European populations.

Evaluation of a Ultraviolet B Light Emitting Diode (LED) for Producing Vitamin D3 in Human Skin.

AIM: A commercially available light emitting diode (LED) that transmitted narrow band ultraviolet B (UVB) radiation was evaluated for its efficacy and efficiency to produce vitamin D3 in human skin. MATERIALS AND METHODS: Human skin samples were obtained from surgical procedures. The LED had peak emission wavelength of 295 nm. Skin samples were exposed to the UVB-LED for varying times and then were analyzed by high-pressure liquid chromatography (HPLC) to determine the vitamin D3 content. RESULTS: There was a statistically significant time- and dose-dependent increase in the percent of 7-dehydrocholesterol that was converted to vitamin D3 in the skin type II samples; 1.3%±0.5, 2.3%±0.6 and 4.5%±1.67 after exposure to 0.75 (11.7 mJ/cm2), 1.5 (23.4 mJ/cm2) and 3 (46.8 mJ/cm2) minimal erythemal doses (MEDs), respectively. CONCLUSION: The UVB-LED was effective and efficient in generating vitamin D3 in human skin, in vitro. The amount of vitamin D3 production increased in a dose-dependent fashion with increased UVB energy. UVB-LEDs can be developed for devices that can efficiently produce vitamin D3 in human skin.

Evaluation of Effectiveness of Ultraviolet Emitting Lamps on the Cutaneous Production of Vitamin D3: Relationship of the Lamps Vitamin D3 Producing Potential to the Production of 8-Hydroxy-2'-Deoxyguanosine and Nitric Oxide.

BACKGROUND/AIM: To assess the effectiveness of three UV emitting lamps on the cutaneous production of vitamin D3, a marker of DNA damage and nitric oxide production in human skin. MATERIALS AND METHODS: Human skin samples (skin types II, III and IV) obtained from surgery were exposed to three different UV emitting lamps for varying times and then extracted and chromatographed to determine the vitamin D3 content. The skin samples exposed to the 3 UV emitting lamps were also evaluated for 8-hydroxy-2'-deoxyguanosine (a marker of DNA damage) and nitric oxide production. RESULTS: It was observed that the spectral output of the 3 lamps had different effects on the cutaneous production of vitamin D3, 8-hydroxy-2'-deoxyguanosine and nitric oxide production. One lamp demonstrated optimal production of vitamin D3 with the least amount of DNA damage and intermediate production of nitric oxide suggesting that it could be developed into a device for treating vitamin D deficiency. CONCLUSION: The spectral output of the experimental UVB emitting lamps significantly influenced the cutaneous production of vitamin D3 8-hydroxy-2'-deoxyguanosine and nitric oxide.

[Vitamin D deficiency in Spanish population. Importance of egg on nutritional improvement]. / Deficiencia en vitamina D de la población española. Importancia del huevo en la mejora nutricional.

INTRODUCTION: Vitamin D is an essential nutrient whose deficiency has been associated with the risk of various chronic diseases such as osteoporosis, hypertension, cardiovascular disease, diabetes, some types of cancer and even overweight and obesity. Although vitamin D can be synthesized at the skin from exposure to sunlight, this source is not always sufficient to meet the needs. For example, the use of sunscreen or the low exposition to the sunlight limits the syntheses. In fact, studies have found that at least half of the Spanish population has vitamin D deficits. Therefore, the dietary contribution is fundamental. Although there are different foods fortified in this vitamin, few products are natural source of it, as fatty fish and eggs. However, according to different studies carried out in the Spanish population, there is a low consumption of this food group. In this way, it would be advisable to promote egg consumption among the population, since this food, in addition to having many nutrients, contains a high amount of vitamin D, which contributes to avoid the appearance of deficiencies and the consequences health consequences that this implies.

INTRODUCCIÓN: La vitamina D es un nutriente esencial cuya deficiencia se ha asociado con el riesgo de aparición de diversas enfermedades crónicas, como la osteoporosis, la hipertensión arterial, la enfermedad cardiovascular, la diabetes, algunos tipos de cáncer e incluso el padecimiento de sobrepeso y obesidad. A pesar de que la vitamina D puede sintetizarse a nivel cutáneo a partir de la exposición a la luz solar, esta fuente no es siempre suficiente para cubrir las necesidades debido al uso de cremas de protección solar y a la baja exposición que se produce durante el invierno, o, como en el caso de las personas enfermas, que salen poco a la calle o se exponen poco a la luz del sol. De hecho, estudios han constatado que al menos la mitad de la población española presenta déficit de vitamina D. Por ello, el aporte dietético es fundamental. Aunque existen diferentes alimentos fortificados con esta vitamina, son pocos los productos que son una fuente natural, entre los que se encuentran los pescados grasos y los huevos. Sin embargo, de acuerdo con diferentes estudios realizados en la población española, existe un bajo consumo de este último grupo de alimentos. De esta manera, sería recomendable fomentar el consumo de huevo entre la población, ya que este alimento, además de tener numerosos nutrientes, contiene una cantidad elevada de vitamina D, lo que contribuye a evitar la aparición de deficiencias y las consecuencias negativas para la salud que ello implica.

Steroid Hormone Vitamin D: Implications for Cardiovascular Disease.

Understanding of vitamin D physiology is important because about half of the population is being diagnosed with deficiency and treated with supplements. Clinical guidelines were developed based on observational studies showing an association between low serum levels and increased cardiovascular risk. However, new randomized controlled trials have failed to confirm any cardiovascular benefit from supplementation in the general population. A major concern is that excess vitamin D is known to cause calcific vasculopathy and valvulopathy in animal models. For decades, administration of vitamin D has been used in rodents as a reliable experimental model of vascular calcification. Technically, vitamin D is a misnomer. It is not a true vitamin because it can be synthesized endogenously through ultraviolet exposure of the skin. It is a steroid hormone that comes in 3 forms that are sequential metabolites produced by hydroxylases. As a fat-soluble hormone, the vitamin D-hormone metabolites must have special mechanisms for delivery in the aqueous bloodstream. Importantly, endogenously synthesized forms are carried by a binding protein, whereas dietary forms are carried within lipoprotein particles. This may result in distinct biodistributions for sunlight-derived versus supplement-derived vitamin D hormones. Because the cardiovascular effects of vitamin D hormones are not straightforward, both toxic and beneficial effects may result from current recommendations.

Adequate vitamin D3 skin synthesis versus erythema risk in the Northern Hemisphere midlatitudes.

Health-optimum-exposure index (HOEI) is proposed to assess if the prescribed amount of vitamin D3 (target value) could be synthesized in the human skin without erythema appearance. It is defined as the ratio between the vitamin D3 quantity received during the maximum allowed outdoor exposure without erythema risk and the target value. Sunbathing is safe for HOEI>1 and 1/HOEI represents a part of minimal erythema dose (MED) necessary to obtain the target value. We examine the following targets: a vitamin D3 quantity equivalent to 1000 IU vitamin D3 taken orally, and an optimal vitamin D3 quantity defined by Krzyscin et al. (2016). The biologically weighted (previtamin D3 and erythemal) doses from the Northern Hemisphere midlatitudinal stations are analyzed to find HOEI dependence on personal and meteorological factors. HOEI depends mostly on the exposed skin area, person's age, and sun elevation at noon but not on the Fitzpatrick skin phototype. We found that only young adults (<21 yr) could safely obtain vitamin D3 quantity, which is equivalent to 1000 IU taken orally, almost throughout the whole year. Duration of such exposures appears <1 h only in the warm subperiods of the year (April-September) for a person with minimal erythema dose of 330 J m-2. Exposing larger part of the body (~30%) enables the oldest persons (>59 yr) to reach 1000 IU target during warm days in spring and summer. The optimal daily vitamin D3 quantity could only be synthesized only by young adults for about 40-60% of days in the May-August period if they expose at least 1/3 part of their body surface area. Vitamin D3 supplementation seems to be necessary over the whole year for the oldest persons with daily dosage of ~2000 IU but reduced to ~1000 IU in summer for sunseekers exposing significant part of the body.

Ultraviolet B Light Emitting Diodes (LEDs) Are More Efficient and Effective in Producing Vitamin D3 in Human Skin Compared to Natural Sunlight.

Vitamin D, the sunshine vitamin is important for health. Those with fat malabsorption disorders malabsorb vitamin D and thus must rely on cutaneous production of vitamin D3. Vitamin D3 is generated secondary to exposure to ultraviolet B (UVB) radiation (whether from the sun or from an artificial source). Light emitting diodes (LEDs) have been developed to emit ultraviolet radiation. Little is known about the efficiency of UVB emitting LEDs tuned to different wavelengths for producing vitamin D3 in human skin. Ampoules containing 7-dehydrocholesterol were exposed to a LED that emitted a peak wavelength at 293, 295, 298 or 305 nm to determine their efficiency to produce previtamin D3. The 293 nm LED was best suited for evaluating its effectiveness for producing vitamin D in human skin due to the shorter exposure time. This LED was found to be 2.4 times more efficient in producing vitamin D3 in human skin than the sun in less than 1/60th the time. This has significant health implications for medical device development in the future that can be used for providing vitamin D supplementation to patients with fat malabsorption syndromes as well as patients with other metabolic abnormalities including patients with chronic kidney disease.

Attenuation of UVR-induced vitamin D3 synthesis in a mouse model deleted for keratinocyte lathosterol 5-desaturase.

The lower risk of some internal cancers at lower latitudes has been linked to greater sun exposure and consequent higher levels of ultraviolet radiation (UVR)-produced vitamin D3 (D3). To separate the experimental effects of sunlight and of all forms of D3, a mouse in which UVR does not produce D3 would be useful. To this end we have generated mice carrying a modified allele of sterol C5-desaturase (Sc5d), the gene encoding the enzyme that converts lathosterol to 7-dehydrocholesterol (7-DHC), such that Sc5d expression can be inactivated using the Cre/lox site-specific recombination system. By crossing to mice with tissue-specific expression of Cre or CreER2 (Cre/estrogen receptor), we generated two lines of transgenic mice. One line has constitutive keratinocyte-specific inactivation of Sc5d (Sc5dk14KO). The other line (Sc5dk14KOi) has tamoxifen-inducible keratinocyte-specific inactivation of Sc5d. Mice deleted for keratinocyte Sc5d lose the ability to increase circulating D3 following UVR exposure of the skin. Thus, unlike in control mice, acute UVR exposure did not affect circulating D3 level in inducible Sc5dk14KOi mice. Keratinocyte-specific inactivation of Sc5d was proven by sterol measurement in hair - in control animals lathosterol and cholesta-7,24-dien-3ß-ol, the target molecules of SC5D in the sterol biosynthetic pathways, together constituted a mean of 10% of total sterols; in the conditional knockout mice these sterols constituted a mean of 56% of total sterols. The constitutive knockout mice had an even greater increase, with lathosterol and cholesta-7,24-dien-3ß-ol accounting for 80% of total sterols. In conclusion, the dominant presence of the 7-DHC precursors in hair of conditional animals and the lack of increased circulating D3 following exposure to UVR reflect attenuated production of the D3 photochemical precursor 7-DHC and, consequently, of D3 itself. These animals provide a useful new tool for investigating the role of D3 in UVR-induced physiological effects and, more broadly, for investigations of the cholesterol synthetic pathway in the skin and other targeted tissues.

Plasma transport of ergocalciferol and cholecalciferol and their 25-hydroxylated metabolites in dairy cows.

In cattle, there are 2 significant forms of vitamin D: ergocalciferol (ERG) from fungi on roughage and cholecalciferol (CHO) from vitamin supplements or endogenous synthesis in the skin. The hypothesis of the present study is that vitamin D from the 3 sources is transported in different plasma fractions in the body. This is hypothesized to explain the lower efficiency of ERG compared to CHO in securing a sufficient plasma status of 25-hydroxyvitamin D and explain the inefficient excretion of dietary CHO into milk compared to endogenous CHO. Twenty vitamin D-depleted cows were assigned to 5 treatments: D2, housed indoor and fed 625-µg/d (25.000 IU) ERG; D3, housed indoor and fed 625-µg/d CHO; D2+D3, housed indoor and fed 625-µg/d ERG and 625-µg/d CHO; SUN, let out for daily pasture to facilitate CHO synthesis from sunlight; and D2+SUN, fed 625-µg/d ERG and let out for daily pasture. Blood samples were taken twice weekly and plasma fractionated by ultracentrifugation into 3 fractions: light lipoprotein (LLP), heavy lipoprotein (HLP), and protein and analyzed for content of ERG and CHO and their liver derived metabolites 25-hydroxyergocalciferol (25ERG) and 25-hydroxycholecalciferol (25CHO), respectively. Liver biopsies were taken on the last day of the study to asses gene expression related to vitamin D metabolism. During 4 wk of study, the vitamin D status in plasma increased to 19.3 to 22.8 ng/mL 25ERG in ERG-treated cows with the highest concentration in D2 (P ≤ 0.05) and to 25.0 to 33.4 ng/mL 25CHO in pasture or CHO-treated cows with the highest concentration in SUN (P ≤ 0.01). In plasma fractions, CHO was mainly found in the HLP fraction, whereas 25CHO was almost exclusively found in the protein fraction, probably due to its reported high binding affinity to vitamin D-binding protein. About 70% to 90% of 25ERG was found in the protein fraction and the remaining 25ERG was found in HLP, whereas ERG was found in both HLP and LLP fractions. In liver tissue, the expression of vitamin D-25-hydroxylase was lower in D2+D3 (P ≤ 0.05) and SUN (P ≤ 0.05) than that in the remaining groups, and the vitamin D receptor was expressed in the liver to a larger extent in D2+SUN than that in D2+D3 (P ≤ 0.05) and SUN (P ≤ 0.05). In conclusion, different plasma transport mechanisms may explain the lower physiological efficiency of ERG compared to CHO in securing the vitamin D status in plasma but do not explain the lower efficiency of synthetic CHO compared to endogenous CHO from sunlight or UV light in securing a high CHO content in milk.

Physiological limit of the daily endogenous cholecalciferol synthesis from UV light in cattle.

The link between UV light (sunlight) and endogenous cholecalciferol (vitamin D3 ) synthesis in the skin of humans has been known for more than a 100 years, since doctors for the first time successfully used UV light to cure rickets in children. Years later, it was shown that UV light also had a significant effect on the cholecalciferol status in the body of cattle. The cholecalciferol status in the body is measured as the plasma concentration of 25-hydroxycholecalciferol, which in cattle and humans is the major circulating metabolite of cholecalciferol. Very little is, however, known about the quantitative efficiency of UV light as a source of cholecalciferol in cattle nutrition and physiology. Hence, the aim of this study was to determine the efficiency of using UV light for increasing the plasma 25-hydroxycholecalciferol concentration in cholecalciferol-deprived cattle. Twelve cows deprived of cholecalciferol for 6 months were divided into three treatment groups and exposed to UV light for 30, 90 or 120 min/day during 28 days. UV-light wavelengths ranged from 280 to 415 nm and 30-min exposure to the UV light was equivalent to 60-min average summer-sunlight exposure at 56 °N. Blood samples were collected every 3-4 days and analysed for 25-hydroxycholecalciferol and cholecalciferol. Results showed that increasing the exposure time from 90-120 min/day did not change the slope of the daily increase in plasma 25-hydroxycholecalciferol. Hence, it appears that cholecalciferol-deprived dairy cattle are able to increase their plasma 25-hydroxycholecalciferol concentration by a maximum of 1 ng/ml/day from UV-light exposure.

The action spectrum for vitamin D3: initial skin reaction and prolonged exposure.

Vitamin D3 photosynthesis in the skin is formulated as a set of reaction equations, including side-reactions to lumisterol, tachysterol and toxisterols, and the accompanying reverse reactions, isomerisation of previtamin D3 to vitamin D3 and photodegradation of vitamin D3. The solution of this set is given for the stationary irradiance spectrum. The effective action spectrum for the instantaneous vitamin D3 production changes shape as a function of exposure, and therefore, no single action spectrum can be used. We assessed the action spectrum for unexposed skin and for skin that has been exposed to 7.5 Standard Erythemal Doses (SED). We constructed two new estimates: (1) the RIVM action spectrum, based on absorption spectra, quantum yields and skin transmission spectra, and (2) the modified QUT action spectrum, which is adjusted for self-absorption and skin transmission. For previously unexposed skin, the modified QUT action spectrum gives a qualitatively similar, but larger estimate than the RIVM action spectrum. We have not been able to solve the lack of quantitative agreement between the vitamin D production estimates from the three action spectrum estimates (RIVM, modified QUT and CIE). All new action spectra have stronger emphasis on the short wavelengths than the CIE action spectrum. We showed that, for wavelengths larger than 300 nm, the bandwidth that was used in the experiment that formed the basis of the CIE action spectrum, gives a red-shift of about 1 nm. Generally, with the formation of previtamin D3, the return reaction to provitamin D3 limits the production of vitamin D3. After some exposure, the new action spectrum has negative values for the longer wavelengths in the UVB. For the RIVM action spectrum, this happens after 7.5 SED, for the modified QUT action spectrum already after 1.25 SED, and after 7.5 SED the net production rate is largely cancelled. Thus prolonged exposure of previously unexposed skin saturates vitamin D3 formation. For maximum vitamin D production after 1.25 SED, sunscreens should block wavelengths larger than 310 nm. Sunscreens that block only UVB could result in reduction in vitamin D production after prolonged exposure, or even a destruction of vitamin D that has just been formed.

Solar Simulators for Healthy Vitamin D Synthesis.

BACKGROUND/AIM: The angular distribution of solar radiance and its spectral characteristics is required for the determination of vitamin D3 production in humans. MATERIALS AND METHODS: The vitamin D3 weighted exposure can be calculated by integrating the incident solar spectral radiance over all relevant parts of the human body. A novel instrument allowing simultaneous measurements of spectral radiance from more than 100 directions has been developed. A large solar simulator for controlled experiments is described. RESULTS: In summer it is relatively easy to obtain sufficient vitamin D because sun exposure times are short. In winter solstice vitamin D3 cannot be obtained with realistic clothing even if the exposure were extended to all daylight hours. CONCLUSION: Improved and controlled experiments to determine vitamin D3 production are required to assess the positive effects of solar UV radiation and to assess its natural variability.

Regional and seasonal variations in ultraviolet B irradiation and vitamin D synthesis in India.

UNLABELLED: Evaluation of ultraviolet B index (UVBI) and its impact on vitamin D synthesis is important. We observed the maximum UVBI between 11 am and 1 pm. There was no increase in serum 25(OH)D levels following sun exposure during winter as the UVBI was significantly low, emphasizing the need for vitamin D supplementation during these months. INTRODUCTION: The amount of vitamin D3 synthesizing UVB irradiation (290-320 nm) reaching the earth's surface at different altitudes and seasons in different parts of India and it's impact on vitamin D synthesis has not been well studied. METHODS: The hourly UVB index (UVBI) from 10 am to 3 pm everyday for 12 months was measured by a solar meter in 4 different zones (North, Northeast, West and South) of the country. To study the impact of sun light exposure on vitamin D synthesis during winter, healthy school children aged 10-15 years were exposed to sunlight for a period of 30 min per day, between 11 am to 12 noon with 10 % body surface area, for 4 weeks. The main outcome measures were serum 25(OH)D, PTH, calcium, phosphate, and alkaline phosphatase levels before and after sun exposure. RESULTS: The mean UVBI was highest between 11 am and 1 pm throughout the year in all locations. The highest UVBI was recorded from the North zone (4.5 ± 2.7 µW/Cm(2)), while the least was recorded in the Northeast zone (2.1 ± 1.2 µW/Cm(2)). UVBI readings in the Northeast zone were consistently low throughout the year, while all the other three zones showed significant seasonal fluctuations. Surprisingly, we observed a significant decrease in serum 25(OH)D levels from baseline (6.3 ± 4.6 to 5.1 ± 2.7 ng/mL; p < 0.001) despite sun exposure. CONCLUSION: The mean UVBI was highest between 11 am and 1 pm throughout the year in all locations. No increase in the serum 25(OH)D levels was observed following sun exposure in winter, emphasizing the need for vitamin D supplementation during these months.

Size of the exposed body surface area, skin erythema and body mass index predict skin production of vitamin D.

BACKGROUND: Cholecalciferol (vitamin D3), produced in the skin by UVB irradiation (290-315nm) of 7-dehydrocholesterol, is metabolized in the liver into 25-hydroxyvitamin D [25(OH)D] which is a major circulating metabolite. AIM: To examine changes in serum concentrations of cholecalciferol and its metabolites after UVB exposure of different skin areas. METHODS: 21 healthy Caucasians (skin type II and III, aged 23-47years) were exposed to broadband UVB (290-320nm) and randomized to either exposure to one minimal erythema dose given as a single dose, or a suberythemic dose given for 3 subsequent days. The following areas were exposed: face and back of hands, upper half of the body and the whole body, respectively. Serum cholecalciferol and 25(OH)D were measured immediately before start and 24h after the 1st and last exposure, respectively. RESULTS: Subjects with whole body exposure had an average S-cholecalciferol increase per dose unit of 0.18ngml(-1)mJ(-1)cm(2), 0.95 CI: (0.16, 0.20), upper body treatment 0.13ngml(-1)mJ(-1)cm(2), 0.95 CI: (0.10, 0.15) and face and hands exposure 0.013ngml(-1)mJ(-1)cm(2), 0.95 CI: (-0.012, 0.037). The increase in cholecalciferol correlated positively to the UVB dose and skin erythema and negatively to body mass index (BMI) when controlling for other factors. Exposure of face and hands induces smaller cholecalciferol production in comparison with exposure of larger skin areas. CONCLUSION: Size of the exposed skin area, UVB dose, skin erythema and BMI were the major determinants for serum levels of skin synthesized cholecalciferol. Exposure of hands and face induces smaller cholecalciferol production in comparison with exposure of larger skin areas.

Vitamin D production after UVB exposure - a comparison of exposed skin regions.

BACKGROUND: Cholecalciferol is an essential steroid produced in the skin by solar ultraviolet B radiation (UVB 290-315nm). Skin production of cholecalciferol depends on factors affecting UVB flux, age and exposed skin area. PURPOSE: Serum cholecalciferol and 25-hydroxyvitamin D3 [25(OH)D3] concentrations were measured after UVB irradiation of 3 different skin areas to compare the skin capacity to produce vitamin D in different anatomic sites in the same individuals. METHOD: Ten voluntary Caucasians (skin photo type II & III, aged 48±12years (±SD)) were exposed to broadband UVB (280-320nm) between February and April. Hands and face, upper body and whole body were exposed to a suberythemic dose of UVB (median 101mJ/cm(2) (min 66, max 143)) (for 3 subsequent days 24h apart with a wash out period of about 3weeks (median 18days (min 11, max 25)) between the exposures of respective area. Serum concentrations of cholecalciferol and 25(OH)D3, were measured immediately before the first and 24h after the last dose of radiation. RESULTS: There was a significantly higher increase in serum cholecalciferol after UVB exposure of the two larger skin areas compared to face and hands, but no difference in increase was found between upper body and whole body exposures. CONCLUSION: Exposure of a larger skin area was superior to small areas and gave greater increase in both serum cholecalciferol and serum 25(OH)D3 concentrations. However, exposure of face and hands, i.e. only 5% of the body surface area, was capable of increasing serum concentrations of 25(OH)D3.