Ultraviolet radiation, vitamin D and the development of obesity, metabolic syndrome and type-2 diabetes

The relationship between altitude and BMI varies across low- and middle-income countries

OBJECTIVES

Studies suggest that living at high altitude decreases obesity risk, but this research is limited to single-country analyses. We examine the relationship between altitude and body mass index (BMI) among women living in a diverse sample of low- and middle-income countries.

MATERIALS AND METHODS

Using Demographic and Health Survey data from 1 583 456 reproductive age women (20-49 years) in 54 countries, we fit regression models predicting BMI and obesity by altitude controlling for a range of demographic factors-age, parity, breastfeeding status, wealth, and education.

RESULTS

A mixed-effects model with country-level random intercepts and slopes predicts an overall -0.162 kg/m2 (95% CI -0.220, -0.104) reduction in BMI and lower odds of obesity (OR 0.90, 95% CI 0.87, 0.95) for every 200 m increase in altitude. However, countries vary dramatically in whether they exhibit a negative or positive association between altitude and BMI (34 countries negative, 20 positive). Mixed findings also arise when examining odds of obesity.

DISCUSSION

We show that past findings of declining obesity risk with altitude are not universal. Increasing altitude predicts slightly lower BMIs at the global level, but the relationship within individual countries varies in both strength and direction.

Associations of the neighbourhood built and natural environment with cardiometabolic health indicators: A cross-sectional analysis of environmental moderators and behavioural mediators

BACKGROUND

Most studies examining the effects of neighbourhood urban design on cardiometabolic health focused solely on the built or natural environment. Also, they did not consider the roles of neighbourhood socio-economic status (SES) and ambient air pollution in the observed associations, and the extent to which these associations were mediated by physical activity and sedentary behaviours.

METHODS

We used data from the AusDiab3 study (N = 4141), a national cohort study of Australian adults to address the above-mentioned knowledge gaps. Spatial data were used to compute indices of neighbourhood walkability (population density, intersection density, non-commercial land use mix, commercial land use), natural environment (parkland and blue spaces) and air pollution (annual average concentrations of nitrogen dioxide (NO2) and fine particulate matter <2.5 μm in diameter (PM2.5)). Census indices were used to define neighbourhood SES. Clinical assessments collected data on adiposity, blood pressure, blood glucose and blood lipids. Generalised additive mixed models were used to estimate associations.

RESULTS

Neighbourhood walkability showed indirect beneficial associations with most indicators of cardiometabolic health via resistance training, walking and sitting for different purposes; indirect detrimental associations with the same indicators via vigorous gardening; and direct detrimental associations with blood pressure. The neighbourhood natural environment had beneficial indirect associations with most cardiometabolic health indicators via resistance training and leisure-time sitting, and beneficial direct associations with adiposity and blood lipids. Neighbourhood SES and air pollution moderated only a few associations of the neighbourhood environment with physical activity, blood lipids and blood pressure.

CONCLUSIONS

Within a low-density and low-pollution context, denser, walkable neighbourhoods with good access to nature may benefit residents' cardiometabolic health by facilitating the adoption of an active lifestyle. Possible disadvantages of living in denser neighbourhoods for older populations are having limited opportunities for gardening, higher levels of noise and less healthy dietary patterns associated with eating out.

The role of light pollution in mammalian metabolic homeostasis and its potential interventions: A critical review

Irregular or unnatural artificial light causes severe environmental stress on the survival and health of organisms, which is rapidly becoming a widespread new type of environmental pollution. A series of disruptive behaviors to body homeostasis brought about by light pollution, including metabolic abnormalities, are likely to be the result of circadian rhythm disturbances. Recently, the proposed role of light pollution in metabolic dysregulation has accelerated it into an emerging field. Hence, the regulatory role of light pollution in mammalian metabolic homeostasis is reviewed in this contribution. Light at night is the most widely affected type of light pollution, which disrupts metabolic homeostasis largely due to its disruption of daily food intake patterns, alterations of hormone levels such as melatonin and glucocorticoids, and changes in the rhythm of inflammatory factor production. Besides, light pollution impairs mammalian metabolic processes in an intensity-, photoperiod-, and wavelength-dependent manner, and is also affected by species, gender, and diets. Nevertheless, metabolic disorders triggered by light pollution are not irreversible to some extent. Potential interventions such as melatonin supplementation, recovery to the LD cycle, time-restricted feeding, voluntary exercise, wearing blue light-shied goggles, and bright morning light therapy open a bright avenue to prevent light pollution. This work will help strengthen the relationship between light information and metabolic homeostasis and provide new insights for the better prevention of metabolic disorders and light pollution.

Ultraviolet B Irradiation Alters the Level and miR Contents of Exosomes Released by Keratinocytes in Diabetic Condition

Ultraviolet B (UVB) stimulates the generation of extracellular vesicles, which elicit systemic effects. Here, we studied whether UVB affects the release and microRNA (miR) content of keratinocyte exosomes (EXs) in diabetic conditions. In vitro, we examined the UVB effects on affecting EX release from keratinocyte HaCaT cells (HaCaT‐EX) pretreated with high glucose. HaCaT‐EX functions were evaluated on Schwann cells (SCs). In vivo, UVB‐induced miR change in skin EXs of diabetic db/db mice was analyzed. The miRs of interest were validated in HaCaT‐EXs. We found that: (1) UVB promoted HaCaT‐EX generation in dose‐ and time‐dependent manners; 100 and 1800 J m⁻² of UVB had the most prominent effect and were selected as effective low‐ and high‐fluence UVB in vitro. (2) A total of 13 miRs were differentially expressed >3‐fold in skin EXs in UVB‐treated db/db mice; miR‐126 was the most up‐regulated by low‐fluence UVB. (3) Functional studies revealed that the SC viability was improved by low‐fluence UVB HaCaT‐EXs, while worsened by high‐fluence UVB HaCaT‐EXs. (4) MiR‐126 inhibitor attenuated the effects induced by low‐fluence UVB HaCaT‐EXs. Our data have demonstrated that low‐ and high‐fluence UVBs promote HaCaT‐EX generation but differentially affect exosomal miR levels and functions under diabetic conditions.

A Bidirectional Mendelian Randomization Study to evaluate the causal role of reduced blood vitamin D levels with type 2 diabetes risk in South Asians and Europeans

Context

Multiple observational studies have reported an inverse relationship between 25-hydroxyvitamin D concentrations (25(OH)D) and type 2 diabetes (T2D). However, the results of short- and long-term interventional trials concerning the relationship between 25(OH)D and T2D risk have been inconsistent.

Objectives and methods

To evaluate the causal role of reduced blood 25(OH)D in T2D, here we have performed a bidirectional Mendelian randomization study using 59,890 individuals (5,862 T2D cases and 54,028 controls) from European and Asian Indian ancestries. We used six known SNPs, including three T2D SNPs and three vitamin D pathway SNPs, as a genetic instrument to evaluate the causality and direction of the association between T2D and circulating 25(OH)D concentration.

Results

Results of the combined meta-analysis of eight participating studies showed that a composite score of three T2D SNPs would significantly increase T2D risk by an odds ratio (OR) of 1.24, p = 1.82 × 10^–32; Z score 11.86, which, however, had no significant association with 25(OH)D status (Beta -0.02nmol/L ± SE 0.01nmol/L; p = 0.83; Z score -0.21). Likewise, the genetically instrumented composite score of 25(OH)D lowering alleles significantly decreased 25(OH)D concentrations (-2.1nmol/L ± SE 0.1nmol/L, p = 7.92 × 10^–78; Z score -18.68) but was not associated with increased risk for T2D (OR 1.00, p = 0.12; Z score 1.54). However, using 25(OH)D synthesis SNP (DHCR7; rs12785878) as an individual genetic instrument, a per allele reduction of 25(OH)D concentration (-4.2nmol/L ± SE 0.3nmol/L) was predicted to increase T2D risk by 5%, p = 0.004; Z score 2.84. This effect, however, was not seen in other 25(OH)D SNPs (GC rs2282679, CYP2R1 rs12794714) when used as an individual instrument.

Conclusion

Our new data on this bidirectional Mendelian randomization study suggests that genetically instrumented T2D risk does not cause changes in 25(OH)D levels. However, genetically regulated 25(OH)D deficiency due to vitamin D synthesis gene (DHCR7) may influence the risk of T2D.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12937-021-00725-1.

Investigating the Potential for Ultraviolet Light to Modulate Morbidity and Mortality From COVID-19: A Narrative Review and Update

During the COVID-19 (coronavirus disease of 2019) pandemic, researchers have been seeking low-cost and accessible means of providing protection from its harms, particularly for at-risk individuals such as those with cardiovascular disease, diabetes and obesity. One possible way is via safe sun exposure, and/or dietary supplementation with induced beneficial mediators (e.g., vitamin D). In this narrative review, we provide rationale and updated evidence on the potential benefits and harms of sun exposure and ultraviolet (UV) light that may impact COVID-19. We review recent studies that provide new evidence for any benefits (or otherwise) of UV light, sun exposure, and the induced mediators, vitamin D and nitric oxide, and their potential to modulate morbidity and mortality induced by infection with SARS-CoV-2 (severe acute respiratory disease coronavirus-2). We identified substantial interest in this research area, with many commentaries and reviews already published; however, most of these have focused on vitamin D, with less consideration of UV light (or sun exposure) or other mediators such as nitric oxide. Data collected to-date suggest that ambient levels of both UVA and UVB may be beneficial for reducing severity or mortality due to COVID-19, with some inconsistent findings. Currently unresolved are the nature of the associations between blood 25-hydroxyvitamin D and COVID-19 measures, with more prospective data needed that better consider lifestyle factors, such as physical activity and personal sun exposure levels. Another short-coming has been a lack of measurement of sun exposure, and its potential to influence COVID-19 outcomes. We also discuss possible mechanisms by which sun exposure, UV light and induced mediators could affect COVID-19 morbidity and mortality, by focusing on likely effects on viral pathogenesis, immunity and inflammation, and potential cardiometabolic protective mechanisms. Finally, we explore potential issues including the impacts of exposure to high dose UV radiation on COVID-19 and vaccination, and effective and safe doses for vitamin D supplementation.

Early-Life Environmental Exposures and Childhood Obesity: An Exposome-Wide Approach

BACKGROUND

Chemical and nonchemical environmental exposures are increasingly suspected to influence the development of obesity, especially during early life, but studies mostly consider single exposure groups.

OBJECTIVES

Our study aimed to systematically assess the association between a wide array of early-life environmental exposures and childhood obesity, using an exposome-wide approach.

METHODS

The HELIX (Human Early Life Exposome) study measured child body mass index (BMI), waist circumference, skinfold thickness, and body fat mass in 1,301 children from six European birth cohorts age 6-11 y. We estimated 77 prenatal exposures and 96 childhood exposures (cross-sectionally), including indoor and outdoor air pollutants, built environment, green spaces, tobacco smoking, and biomarkers of chemical pollutants (persistent organic pollutants, metals, phthalates, phenols, and pesticides). We used an exposure-wide association study (ExWAS) to screen all exposure-outcome associations independently and used the deletion-substitution-addition (DSA) variable selection algorithm to build a final multiexposure model.

RESULTS

The prevalence of overweight and obesity combined was 28.8%. Maternal smoking was the only prenatal exposure variable associated with higher child BMI (z-score increase of 0.28, 95% confidence interval: 0.09, 0.48, for active vs. no smoking). For childhood exposures, the multiexposure model identified particulate and nitrogen dioxide air pollution inside the home, urine cotinine levels indicative of secondhand smoke exposure, and residence in more densely populated areas and in areas with fewer facilities to be associated with increased child BMI. Child blood levels of copper and cesium were associated with higher BMI, and levels of organochlorine pollutants, cobalt, and molybdenum were associated with lower BMI. Similar results were found for the other adiposity outcomes.

DISCUSSION

This first comprehensive and systematic analysis of many suspected environmental obesogens strengthens evidence for an association of smoking, air pollution exposure, and characteristics of the built environment with childhood obesity risk. Cross-sectional biomarker results may suffer from reverse causality bias, whereby obesity status influenced the biomarker concentration. https://doi.org/10.1289/EHP5975.

Characterising nitric oxide-mediated metabolic benefits of low-dose ultraviolet radiation in the mouse: a focus on brown adipose tissue

AIMS/HYPOTHESIS

Exposure to sunlight has the potential to suppress metabolic dysfunction and obesity. We previously demonstrated that regular exposure to low-doses of ultraviolet radiation (UVR) reduced weight gain and signs of diabetes in male mice fed a high-fat diet, in part via release of nitric oxide from skin. Here, we explore further mechanistic pathways through which low-dose UVR exerts these beneficial effects.

METHODS

We fed mice with a luciferase-tagged Ucp1 gene (which encodes uncoupling protein-1 [UCP-1]), referred to here as the Ucp1 luciferase transgenic mouse ('Thermomouse') a high-fat diet and examined the effects of repeated exposure to low-dose UVR on weight gain and development of metabolic dysfunction as well as UCP-1-dependent thermogenesis in interscapular brown adipose tissue (iBAT).

RESULTS

Repeated exposure to low-dose UVR suppressed the development of glucose intolerance and hepatic lipid accumulation via dermal release of nitric oxide while also reducing circulating IL-6 (compared with mice fed a high-fat diet only). Dietary nitrate supplementation did not mimic the effects of low-dose UVR. A single low dose of UVR increased UCP-1 expression (by more than twofold) in iBAT of mice fed a low-fat diet, 24 h after exposure. However, in mice fed a high-fat diet, there was no effect of UVR on UCP-1 expression in iBAT (compared with mock-treated mice) when measured at regular intervals over 12 weeks. More extensive circadian studies did not identify any substantial shifts in UCP-1 expression in mice exposed to low-dose UVR, although skin temperature at the interscapular site was reduced in UVR-exposed mice. The appearance of cells with a white adipocyte phenotype ('whitening') in iBAT induced by consuming the high-fat diet was suppressed by exposure to low-dose UVR in a nitric oxide-dependent fashion. Significant shifts in the expression of important core gene regulators of BAT function (Dio2, increased more than twofold), fatty acid transport (increased Fatp2 [also known as Slc27a2]), lipolysis (decreased Atgl [also known as Pnpla2]), lipogenesis (decreased Fasn) and inflammation (decreased Tnf), and proportions of macrophages (increased twofold) were observed in iBAT of mice exposed to low-dose UVR. These effects were independent of nitric oxide released from skin.

CONCLUSIONS/INTERPRETATION

Our results suggest that non-burning (low-dose) UVR suppresses the BAT 'whitening', steatotic and pro-diabetic effects of consuming a high-fat diet through skin release of nitric oxide, with some metabolic and immune pathways in iBAT regulated by UVR independently of nitric oxide.

Sun Exposure: Beyond the Risks

Excessive solar exposure presents well-recognized risks and side effects, solar radiation being the most important environmental factor concerning skin cancer. In the last few years, several connections between solar exposure and prevention and/or treatment of several diseases have been discussed, with studies suggesting that regular solar exposure may be beneficial for conditions such as colorectal, breast, prostate, and pancreatic cancer; non-Hodgkin lymphoma; arterial hypertension; obesity; type 2 diabetes mellitus and metabolic syndrome; nonalcoholic hepatic steatosis; multiple sclerosis; Alzheimer disease; and several psychiatric disturbances. In most cases, UV radiation's beneficial effects are mediated through vitamin D; however, studies show that in other instances other mediators are responsible for these associations, specifically nitric oxide. Moderation is therefore essential, as a strict strategy of total sun avoidance may be inadequate.

Changes in the total ozone content over the period 2006 to 2100 and the effects on the erythemal and vitamin D effective UV doses for South America and Antarctica

Recent studies show that the ozone layer will recover by the middle part of this century. This is a significant result arising from the Montreal Protocol, and highlights the success of this environmental protection agreement. Climate change projections show that Total Ozone Content (TOC) levels will increase significantly by the end of this century, mainly at higher latitudes. This increase may result in a reduction of the adverse effects of UV radiation overexposure. By contrast, reduced UV radiation levels at the surface of the Earth can result in reduced levels of vitamin D synthesis among the inhabitants of these regions. In this study we provide estimates for the UVI, erythemal, and vitamin-D weighted daily doses for ten different locations in South America and Antarctica. Our calculations were based on ozone projections provided by climate models set forth in the last IPCC report. Results show that the increase of TOC levels in middle and high latitude regions may result in decreased UVI and UV doses throughout the century. In high latitudes, erythemal doses and vitamin D synthesis doses may be reduced by up to 22 and 39%, respectively, if anthropogenic emissions continue to rise throughout the century. Furthermore, there may be reductions of up to 9 and 12%, respectively, in mid-latitudes (20°S to 35°S). Significant variations at Equatorial sites were not observed. In most of South America, the attenuation in UVR caused by increases in TOC during the 21^st century is neither enough to promote protective effects from this radiation, nor for the lack of UVR for vitamin D synthesis. The incidence of UVR in tropical and sub-tropical areas of the continent will continue to be a public health risk for the entire 21^st century during all seasons, regardless of the climatic scenarios. Our results can be used as an important tool for health studies focusing on the excess and/or lack of sun exposure.

Systematic Review of the Effects of Ultraviolet Radiation on Markers of Metabolic Dysfunction

Emerging findings suggest that exposure to ultraviolet wavelengths of sunlight modulates metabolic function. Here we review the metabolic effects of exposure to ultraviolet radiation (UVR), focusing on the effects of phototherapies (that administer UVR), and advice to increase sun exposure in individuals enrolled in clinical trials and intervention studies. We identified 25 studies in which the effects of UVR on metabolic outcomes were examined, including: narrowband ultraviolet B phototherapy (nbUVB, n = 12); psoralen ultraviolet A phototherapy (n = 4); other types of UVR phototherapy (n = 5); and sun exposure advice (n = 5). Most studies recruited a small number of participants (≤100), who were middle-aged individuals undergoing treatment for psoriasis flare, with phototherapy or sun exposure advice administered for ≤12 weeks. Data obtained at baseline were usually compared with an endpoint following treatment with UVR, for a limited number of outcomes. There were few studies in which markers of glucose metabolism were assessed, with some beneficial effects of sun exposure (but not phototherapy) reported. LDL-cholesterol levels were lower in individuals receiving sun exposure advice, while treatment with nbUVB reduced blood concentrations of inflammatory markers (C-reactive protein and interleukin-6). Future studies should focus on determining whether the effects of these interventions change with time, and if they are dependent on the source of UVR (i.e. phototherapy or sun exposure) and wavelength(s) of light administered. Furthermore, studies need to measure a variety of (clinical) markers of glucose metabolism, adiposity and inflammation, control for factors such as skin type and sex, and stratify participants for metabolic disease diagnosis.

Significant Associations Between Sun Exposure and Adiposity Were Not Observed in Breast and Prostate Cancer Patients in a Cross-sectional Analysis

Obesity is a significant health problem worldwide. Exposure to low-dose ultraviolet radiation (like that in sunlight) suppresses the development of obesity in mice; however, the nature of the associations between sun exposure and adiposity is not well understood in humans. The present study characterized cross-sectional relationships between sun exposure and adiposity in a convenience cohort of breast (n = 269; mean age = 58 years) and prostate (n = 78; mean age = 69 years) cancer patients. Participants were enrolled in a 3-month exercise program in Perth, Australia. Self-reported questionnaires measured time spent outdoors (previous week, winter and summer), sex, age, treatment received and physical activity levels. Adiposity measures included body mass index, waist-hip ratio and body fat percentage (measured via DXA). In unadjusted models, greater time spent outdoors across all times was significantly associated with lower waist-hip ratio, while greater time spent outdoors in the last winter was associated with lower body fat percentage, but not when stratified by sex. There were no statistically significant associations between time spent outdoors and adiposity after adjusting for sex, age, treatments received and physical activity. Longitudinal studies in larger populations may elucidate significant associations not found in our study due to the cross-sectional design and power limitations.

Regular exposure to non-burning ultraviolet radiation reduces signs of non-alcoholic fatty liver disease in mature adult mice fed a high fat diet: results of a pilot study

Objective

Obesity often emerges in middle age, increasing risk for metabolic disorders. Our previous preclinical experiments identified that chronic exposure to non-burning ultraviolet radiation, like that achieved through sun exposure, prevented weight gain and signs of metabolic dysfunction in young adult mice fed a high fat diet. Our objective was to perform a pilot study to estimate the effect size of ongoing exposure to sub-erythemal (non-burning, low dose) UVB (1 kJ/m²) radiation on measures of adiposity, food intake and physical activity in ‘mature’ adult C57Bl/6J male mice fed a high fat diet for 12 weeks.

Results

The severity of liver steatosis, fibrosis and inflammation were reduced in older adult mice exposed twice a week to ultraviolet radiation (from 29 weeks of age), compared to mock-irradiated mice, with some evidence for reduced hepatic mRNAs for tnf and tgfß1 (not fatp2 nor fasN). Power analyses suggested that up to 24 mice per treatment would be required in future experiments to detect a significant effect on some markers of adiposity such as body weight gain. Our studies suggest frequent exposure to low levels of sunlight may reduce the severity of hepatic steatosis induced in older adults living in environments of high caloric intake.

Electronic supplementary material

The online version of this article (10.1186/s13104-019-4112-8) contains supplementary material, which is available to authorized users.

Does sunlight protect us from cancer?

The Ultraviolet (UV) radiation contained in sunlight is a powerful mutagen and immune suppressant which partly explains why exposure to solar UV is the biggest risk factor for the development of cutaneous tumours. Evidence is building that sunlight may be protective against some internal malignancies. Because patients with these tumours are often vitamin D deficient, this has led some to propose that vitamin D supplementation will be beneficial in the treatment of these cancers. However, the results from already completed trials have been disappointing which has given weight to the argument that there must be something else about sunlight that explains its cancer-protecting properties.

Predictors of 25-hydroxyvitamin D status among individuals with metabolic syndrome: a cross-sectional study

BACKGROUND

The risk of metabolic syndrome can be influenced by inadequate vitamin D levels, and exposure to sunlight is the main external source of vitamin D. The present study assessed the influence of environmental, biological, and nutritional factors in relation to seasonal 25-hydroxyvitamin D (25OHD) concentration in individuals with metabolic syndrome.

METHODS

This cross-sectional study enrolled 180 individuals with metabolic syndrome aged between 18 and 80 years. The 25OHD concentration was considered the dependent variable; independent variables included age, sex, skin color, use of sunscreen, skin type, sun exposure score, ultraviolet radiation index, geographic location, season, body mass index, waist:hip ratio, waist circumference, parathyroid hormone level, total serum calcium level, and calcium and vitamin D intake.

RESULTS

The average vitamin D in individuals evaluated in summer 32 ± 10 ng/mL was greater than in the winter 26 ± 8 ng/mL (p < 0.017). HDL-cholesterol was the only component of the MetS that differed significantly between the seasons (p < 0.001), showing higher concentrations in autumn 45 ± 8 mg/dL than in summer 35 ± 8 mg/dL. In the multiple regression model, gender, WHR, sun exposure score, and winter vs. summer explained 10% of the variation in 25OHD concentration (p = 0.004).

CONCLUSIONS

Sex, waist:hip ratio, sun exposure, and summer season were predictors of 25OHD status among individuals with metabolic syndrome. HDL-cholesterol was the only component of metabolic syndrome that differed significantly between the seasons.

The effects of two different doses of ultraviolet-A light exposure on nitric oxide metabolites and cardiorespiratory outcomes

Purpose

The present study investigated different doses of ultraviolet-A (UV-A) light on plasma nitric oxide metabolites and cardiorespiratory variables.

Methods

Ten healthy male participants completed three experimental conditions, 7 days apart. Participants were exposed to no light (CON); 10 J cm² (15 min) of UV-A light (UVA10) and 20 J cm² (30 min) of UV-A light (UVA20) in a randomized order. Plasma nitrite [NO₂⁻] and nitrate [NO₃⁻] concentrations, blood pressure (BP), and heart rate (HR) were recorded before, immediately after exposure and 30 min post-exposure. Whole body oxygen utilization (\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$${{\dot{V}}}{\rm O}_{2}$$\end{document}V˙O2), resting metabolic rate (RMR) and skin temperature were recorded continuously.

Results

None of the measured parameters changed significantly during CON (all P > 0.05). \documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$${{\dot{V}}}{\rm O}_{2}$$\end{document}V˙O2 and RMR were significantly reduced immediately after UVA10 (P < 0.05) despite no change in plasma [NO₂⁻] (P > 0.05). Immediately after exposure to UVA20, plasma [NO₂⁻] was higher (P = 0.014) and \documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$${{\dot{V}}}{\rm O}_{2}$$\end{document}V˙O2 and RMR tended to be lower compared to baseline (P = 0.06). There were no differences in [NO₂⁻] or \documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$${{\dot{V}}}{\rm O}_{2}$$\end{document}V˙O2 at the 30 min time point in any condition. UV-A exposure did not alter systolic BP, diastolic BP or MAP (all P > 0.05). UV-A light did not alter plasma [NO₃⁻] at any time point (all P > 0.05).

Conclusions

This study demonstrates that a UV-A dose of 20 J cm² is necessary to increase plasma [NO₂⁻] although a smaller dose is capable of reducing \documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$${{\dot{V}}}{\rm O}_{2}$$\end{document}V˙O2 and RMR at rest. Exposure to UV-A did not significantly reduce BP in this cohort of healthy adults. These data suggest that exposure to sunlight has a meaningful acute impact on metabolic function.

Pathogenetic role of vitamin D deficiency in the development of menstrual dysfunction in pubertal girls: a literature review

In the literature review, 50 scientific sources surrounding the problem of vitamin D deficiency, 80% of which amounted to the issuance of the last 5 years, have been analyzed. Despite the impact of vitamin D deficiency on the health of children and adolescents has been studied for a long time, the information on the role of vitamin D in the formation of menstrual function in pubertal girls is scant and ambiguous. Among the hypotheses of menstrual dysfunction with vitamin D deficiency, neurohumoral regulation of the hypothalamic-pituitary-ovarian system is considered to be essential due to the localization of vitamin D receptors (VDR), unlike other vitamins, in the nuclei of various tissues and organs. However, in the last 10 years, data on the role of genetic polymorphism of the VDR gene in the pathogenesis of various manifestations of menstrual dysfunction have been accumulated. Some studies indicated a beneficial effect of cholecalciferol on such menstrual dysfunctions as oligomenorrhea and dysmenorrhea. Regarding numerous data on the role of vitamin D, both traditional and recently published, there is a strong correlation between vitamin D deficiency and other various factors, determining a wide range of polymorphic clinical manifestations where menstrual dysfunction is essential in girls at the age of puberty.

Sun Exposure and Its Effects on Human Health: Mechanisms through Which Sun Exposure Could Reduce the Risk of Developing Obesity and Cardiometabolic Dysfunction

Obesity is a significant burden on global healthcare due to its high prevalence and associations with chronic health conditions. In our animal studies, ongoing exposure to low dose ultraviolet radiation (UVR, found in sunlight) reduced weight gain and the development of signs of cardiometabolic dysfunction in mice fed a high fat diet. These observations suggest that regular exposure to safe levels of sunlight could be an effective means of reducing the burden of obesity. However, there is limited knowledge around the nature of associations between sun exposure and the development of obesity and cardiometabolic dysfunction, and we do not know if sun exposure (independent of outdoor activity) affects the metabolic processes that determine obesity in humans. In addition, excessive sun exposure has strong associations with a number of negative health consequences such as skin cancer. This means it is very important to "get the balance right" to ensure that we receive benefits without increasing harm. In this review, we detail the evidence around the cardiometabolic protective effects of UVR and suggest mechanistic pathways through which UVR could be beneficial.