Skin types and epidermal photosynthesis of vitamin D3

Physical Determinants of Vitamin D Photosynthesis: A Review

Vitamin D synthesis by exposure of skin to solar ultraviolet radiation (UVR) provides the majority of this hormone that is essential for bone development and maintenance but may be important for many other health outcomes. This process, which is the only well-established benefit of solar UVR exposure, depends on many factors including genetics, age, health, and behavior. However, the most important factor is the quantity and quality of UVR reaching the skin. Vitamin D synthesis specifically requires ultraviolet B (UVB) radiation that is the minority component (<5%) of solar UVR. This waveband is also the most important for the adverse effects of solar exposure. The most obvious of which is sunburn (erythema), but UVB is also the main cause of DNA damage to the skin that is a prerequisite for most skin cancers. UVB at the Earth's surface depends on many physical and temporal factors such as latitude, altitude, season, and weather. Personal, cultural, and behavioral factors are also important. These include skin melanin, clothing, body surface area exposed, holiday habits, and sunscreen use. There is considerable disagreement in the literature about the role of some of these factors, possibly because some studies have been done by researchers with little understanding of photobiology. It can be argued that vitamin D supplementation obviates the need for solar exposure, but many studies have shown little benefit from this approach for a wide range of health outcomes. There is also increasing evidence that such exposure offers health benefits independently of vitamin D: the most important of which is blood-pressure reduction. In any case, public health advice must optimize risk versus benefit for solar exposure. It is fortunate that the individual UVB doses necessary for maintaining optimal vitamin D status are lower than those for sunburn, irrespective of skin melanin. © 2020 The Authors. JBMR Plus published by Wiley Periodicals LLC. on behalf of American Society for Bone and Mineral Research.

Skin cancer and vitamin D: an update

Exposure of the skin to solar ultraviolet (UV) radiation has both risks and benefits for human health. Absorption of UV-B radiation by DNA results in mutations that underlie the development of skin cancers, as is apparent from genetic studies showing high occurrence of UV signature mutations within these tumors. UV-B radiation is also absorbed by 7-dehydrocholesterol to initiate vitamin D synthesis. In experimental studies vitamin D metabolites enhance apoptosis of malignant cells, inhibit angiogenesis and proliferation and increase differentiation, potentially reducing skin cancer development and improving prognosis after diagnosis. There are some supporting human data. We review the links between sun exposure, vitamin D and skin cancers.

Comparing the effects of sun exposure and vitamin D supplementation on vitamin D insufficiency, and immune and cardio-metabolic function: the Sun Exposure and Vitamin D Supplementation (SEDS) Study

Background

Adults living in the sunny Australian climate are at high risk of skin cancer, but vitamin D deficiency (defined here as a serum 25-hydroxyvitamin D (25(OH)D) concentration of less than 50 nmol/L) is also common. Vitamin D deficiency may be a risk factor for a range of diseases. However, the optimal strategies to achieve and maintain vitamin D adequacy (sun exposure, vitamin D supplementation or both), and whether sun exposure itself has benefits over and above initiating synthesis of vitamin D, remain unclear.

The Sun Exposure and Vitamin D Supplementation (SEDS) Study aims to compare the effectiveness of sun exposure and vitamin D supplementation for the management of vitamin D insufficiency, and to test whether these management strategies differentially affect markers of immune and cardio-metabolic function.

Methods/Design

The SEDS Study is a multi-centre, randomised controlled trial of two different daily doses of vitamin D supplementation, and placebo, in conjunction with guidance on two different patterns of sun exposure. Participants recruited from across Australia are aged 18–64 years and have a recent vitamin D test result showing a serum 25(OH)D level of 40–60 nmol/L.

Discussion

This paper discusses the rationale behind the study design, and considers the challenges but necessity of data collection within a non-institutionalised adult population, in order to address the study aims. We also discuss the challenges of participant recruitment and retention, ongoing engagement of referring medical practitioners and address issues of compliance and participant retention.

Trial registration

Australia New Zealand Clinical Trials Registry: ACTRN12613000290796 Registered 14 March 2013.

A systematic review of the influence of skin pigmentation on changes in the concentrations of vitamin D and 25-hydroxyvitamin D in plasma/serum following experimental UV irradiation

Does skin colour influence the production of vitamin D metabolites following UV irradiation? The paper reviews the studies addressing this important question and discusses possible reasons for the contradictory results.

Vitamin D status: multifactorial contribution of environment, genes and other factors in healthy Australian adults across a latitude gradient

Vitamin D deficiency is common and implicated in risk of several human diseases. Evidence on the relative quantitative contribution of environmental, genetic and phenotypic factors to vitamin D status (assessed by the serum concentration of 25-hydroxyvitamin D, 25(OH)D) in free-living populations is sparse. We conducted a cross-sectional study of 494 Caucasian adults aged 18-61years, randomly selected from the Australian Electoral Roll according to groups defined by age, sex and region (spanning 27°-43°South). Data collected included personal characteristics, sun exposure behaviour, biomarkers of skin type and past sun exposure, serum 25(OH)D concentration and candidate single nucleotide polymorphisms. Ambient ultraviolet radiation (UVR) levels in the month six weeks before blood sampling best predicted vitamin D status. Serum 25(OH)D concentration increased by 10nmol/L as reported time in the sun doubled. Overall, 54% of the variation in serum 25(OH)D concentration could be accounted for: 36% of the variation was explained by sun exposure-related factors; 14% by genetic factors (including epistasis) and 3.5% by direct measures of skin phenotype. Novel findings from this study are demonstration of gene epistasis, and quantification of the relative contribution of a wide range of environmental, constitutional and genetic factors to vitamin D status. Ambient UVR levels and time in the sun were of prime importance but it is nonetheless important to include the contribution of genetic factors when considering sun exposure effects. This article is part of a Special Issue entitled 'Vitamin D Workshop'.

The role of vitamin D in pregnancy and lactation: emerging concepts

Pregnancy is a critical time in the lifecycle of a woman where she is responsible not only for her own well-being, but also that of her developing fetus, a process that continues during lactation. Until recently, the impact of vitamin D status during this period had not been fully appreciated. Data regarding the importance of vitamin D in health have emerged to challenge traditional dogma, and suggest that vitamin D - through its effect on immune function and surveillance - plays a role beyond calcium and bone metabolism on the health status of both the mother and her fetus. Following birth, this process persists; the lactating mother continues to be the main source of vitamin D for her infant. Thus, during both pregnancy and lactation, maternal deficiency predicts fetal and infant deficiency; the significance of this is just beginning to be understood and will be highlighted in this review.

Prevalence of vitamin D deficiency among Turkish, Moroccan, Indian and sub-Sahara African populations in Europe and their countries of origin: an overview

Vitamin D status of nonwestern immigrants in Europe was poor. Vitamin D status of nonwestern populations in their countries of origin varied, being either similar to the immigrant populations in Europe or higher than in European indigenous populations. Vitamin D concentrations in nonwestern immigrant populations should be improved.

PURPOSE

The higher the latitude, the less vitamin D is produced in the skin. Most European countries are located at higher latitudes than the countries of origin of their nonwestern immigrants. Our aim was to compare the serum 25-hydroxyvitamin D (25(OH)D) concentration of nonwestern immigrant populations with those of the population in their country of origin, and the indigenous population of the country they migrated to.

METHODS

We performed literature searches in the "PubMed" and "Embase" databases, restricted to 1990 and later. The search profile consisted of terms referring to vitamin D or vitamin D deficiency, prevalence or cross-sectional studies, and countries or ethnicity. Titles and abstracts were reviewed to identify studies on population-based mean serum 25(OH)D concentrations among Turkish, Moroccan, Indian, and sub-Sahara African populations in Europe, Turkey, Morocco, India, and sub-Sahara Africa.

RESULTS

The vitamin D status of immigrant populations in Europe was poor compared to the indigenous European populations. The vitamin D status of studied populations in Turkey and India varied and was either similar to the immigrant populations in Europe (low) or similar to or even higher than the indigenous European populations (high).

CONCLUSIONS

In addition to observed negative consequences of low serum 25(OH)D concentrations among nonwestern populations, this overview indicates that vitamin D status in nonwestern immigrant populations should be improved. The most efficacious strategy should be the subject of further study.

Population density determines the direction of the association between ambient ultraviolet radiation and type 1 diabetes incidence

BACKGROUND

Type 1 diabetes incidence has increased rapidly over the last 20 years, and ecological studies show inverse latitudinal gradients for both incidence and prevalence. Some studies have found season of birth or season of diagnosis effects. Together these findings suggest an important role for environmental factors in disease etiology.

OBJECTIVE

To examine whether type 1 diabetes incidence varies in relation to ambient ultraviolet radiation (UVR) in Australian children.

METHODS

We used case records of 4773 children aged 0-14 yr from the Australian National Diabetes Register to estimate type 1 diabetes incidence in relation to residential ambient UVR, both as a continuous variable and in four categories. We examined season of birth and season of diagnosis and variation in these parameters and in age at diagnosis, in relation to ambient UVR.

RESULTS

Overall incidence was 20 per 100 000 population with no sex difference. There was a statistically significant trend toward winter diagnosis (adjusted RR = 1.22, 95% CI 1.13-1.33, p<0.001) but no apparent season of birth effect. Incidence in the highest UVR category was significantly lower than in the lowest UVR category (RR = 0.85, 95% CI 0.75-0.96). We found an inverse association between incidence and ambient UVR that was present only at low population densities; at high population densities type 1 diabetes incidence increased with increasing ambient UVR.

CONCLUSION

In low population density, largely rural environments, ambient UVR may better reflect the personal UV dose, with the latter being protective for the development of type 1 diabetes. This effect is lost or reversed in high population density, largely urban, environments.

Vitamin D status during pregnancy and aspects of offspring health

Low maternal vitamin D levels during pregnancy have been linked to various health outcomes in the offspring, ranging from periconceptional effects to diseases of adult onset. Maternal and infant cord 25(OH)D levels are highly correlated. Here, we review the available evidence for these adverse health effects. Most of the evidence has arisen from observational epidemiological studies, but randomized controlled trials are now underway. The evidence to date supports that women should be monitored and treated for vitamin D deficiency during pregnancy but optimal and upper limit serum 25(OH)D levels during pregnancy are not known.

Analyzing adherence to prenatal supplement: does pill count measure up?

Objective. To determine if adherence as measured by pill count would show a significant association with serum-based measures of adherence. Methods. Data were obtained from a prenatal vitamin D supplementation trial where subjects were stratified by race and randomized into three dosing groups: 400 (control), 2000, or 4000 IU vitamin D(3)/day. One measurement of adherence was obtained via pill counts remaining compared to a novel definition for adherence using serum 25-hydroxy-vitamin D (25-OH-D) levels (absolute change in 25(OH)D over the study period and the subject's steady-state variation in their 25(OH)D levels). A multivariate logistic regression model examined whether mean percent adherence by pill count was significantly associated with the adherence measure by serum metabolite levels. Results. Subjects' mean percentage of adherence by pill count was not a significant predictor of adherence by serum metabolite levels. This finding was robust across a series of sensitivity analyses. Conclusions. Based on our novel definition of adherence, pill count was not a reliable predictor of adherence to protocol, and calls into question how adherence is measured in clinical research. Our findings have implications regarding the determination of efficacy of medications under study and offer an alternative approach to measuring adherence of long half-life supplements/medications.

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): Wegener's 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.

Does vitamin D make the world go 'round'?

Abstract Vitamin D has emerged from obscurity, and its effects on various organ systems throughout the body down to the cellular level are being discovered. What was once thought to be a simple hormone affecting only bone and calcium metabolism has shifted. We no longer see vitamin D as a "vitamin" important only in childhood, but as a complex hormone that is involved not only in calcium homeostasis but also in the integrity of the innate immune system. Vitamin D deficiency is linked to inflammatory and long-latency diseases such as multiple sclerosis, rheumatoid arthritis, tuberculosis, diabetes, and various cancers, to name a few. In this review, we trace how we came to view vitamin D and how that view led to one of the largest epidemics of nutrient deficiency beginning in the late 20(th) century. We then discuss the needs of vitamin D in the context of the breastfeeding mother and her infant and child, why breastfed infants are particularly at risk, and what to do about it.

Association between quantitative measures of skin color and plasma 25-hydroxyvitamin D

We examined the relationship between vitamin D and skin color measured by reflectance colorimetry at an exposed and un-exposed site in 321 people. Exposed but not unexposed skin color was associated with better vitamin D status. Sun-exposure was more important than natural skin color in determining vitamin D status in our population.

INTRODUCTION

Vitamin D is obtained through UV synthesis in the skin where melanin limits its synthesis. Ethnicity is often used as a proxy for skin color, but skin color varies considerably. The relation between quantitative measures of skin color and plasma 25-hydroxyvitamin D (25OHD) concentration has not been well described.

METHODS

The aim of this study was to determine the association between constitutive (natural) and sun-induced skin color and 25OHD in a group of Pacific People (n = 87) and Europeans (n = 255) living in NZ (46 degrees S) in summer. Plasma 25OHD was determined and sun-induced (outer fore-arm) and constitutive (upper inner-arm) measured by reflectance colorimetry.

RESULTS

Mean (SD) 25OHD was significantly higher in Europeans than Pacific People, 88 (31) nmol/L vs. 75 (34) nmol/L, respectively. Based on constitutive skin color, 35% of participants were very light, 45% light, 16% intermediate, 4% tanned, and 0% brown or dark. Skin color at the forearm but not constitutive skin color was a significant predictor of 25OHD. Each 10 degrees lower skin color value at the forearm (more tanning) was associated with a 5 nmol/L higher 25OHD (P < 0.001).

CONCLUSIONS

Tanning but not natural skin color was an important determinant of 25OHD. Further study is needed in a population with a higher proportion of darker skin people.

The effect of high-dose vitamin D supplementation on serum vitamin D levels and milk calcium concentration in lactating women and their infants

OBJECTIVE

Improve vitamin D status in lactating women and their recipient infants, and measure breast milk calcium concentration [Ca] as a function of vitamin D regimen.

DESIGN/METHODS

Fully breastfeeding mothers were randomized at 1 month postpartum to 2000 (n = 12) or 4000 (n = 13) IU/day vitamin D for 3 months to achieve optimal vitamin D status [serum 25(OH)D > or =32 ng/mL (80 nmol/L)]. Breast milk [Ca], maternal and infant serum 25(OH)D and serum Ca, and maternal urinary Ca/Cr ratio were measured monthly.

RESULTS

Mothers were similar between groups for age, race, gestation, and birth weight. 25(OH)D increased from 1 to 4 months in both groups (mean +/- SD): +11.5 +/- 2.3 ng/mL for group 2000 (p = 0.002) and +14.4 +/- 3.0 ng/mL for group 4000 (p = 0.0008). The 4000 IU/day regimen was more effective in raising both maternal and infant serum levels and breast milk antirachitic activity than the 2000 IU/day regimen. Breast milk [Ca] fell with continued lactation through 4 months in the 2000 and 4000 IU groups. Decline in breast milk [Ca] was not associated with vitamin D dose (p = 0.73) or maternal 25(OH)D (p = 0.94). No mother or infant experienced vitamin D-related adverse events, and all laboratory parameters remained in the normal range.

CONCLUSION

High-dose vitamin D was effective in increasing 25(OH)D levels in fully breastfeeding mothers to optimal levels without evidence of toxicity. Breast milk [Ca] and its decline in both groups during 1 to 4 months were independent of maternal vitamin D status and regimen. Both the mother and her infant attained improved vitamin D status and maintained normal [Ca].