The vitamin D-folate hypothesis in human vascular health

A Program of Life-Style Modification Improved the Body Weight and Micronutrient Status in Obese Patients after Bariatric Surgery

INTRODUCTION

Bariatric surgery is an efficient approach to rapidly reduce morbid obesity and associated comorbidities. However, approximately one-fourth of patients experience weight and comorbidity recurrence, and both obesity and bariatric surgery can lead to micronutrient deficiencies. Implementing a structured program of lifestyle modification (PLM) might enhance weight loss and improve micronutrient status.

METHODOLOGY

A total of 121 severely obese patients underwent Roux-en-Y gastric bypass (RYGB). Among them, 71 adhered to a PLM involving dietary changes (low- and very-low-calorie Mediterranean diets) and physical exercises (aerobic and resistance training) both before and after surgery, while 50 patients followed a conventional protocol. Anthropometric measurements and serological parameter quantifications were conducted throughout the procedures.

RESULTS

The obese study population, primarily female (76.9%), with an average age of 47.11 ± 9.68, and a body mass index (BMI) of 44.68 ± 5.08 kg/m2, underwent either RYGB with a PLM or a conventional procedure. Before surgery, the PLM group exhibited significant reductions in body weight (6.3%) and phosphoremia compared to the conventional protocol (0.78%). Post-RYGB, the PLM group demonstrated shortened in-hospital stays and further BMI reductions (-16.12 kg/m2) that persisted for up to 2 years. Furthermore, the PLM group experienced increased plasma vitamin D levels (14.79 ng/mL vs. 1.2 ng/mL) for up to 2 years, as well as elevated folic acid (1.52 vs. -0.29 ng/mL) and phosphorus (0.48 vs. 0.06 mg/dL) levels at 1 month and 1 year after intervention, respectively. Notably, these effects were independent of weight loss.

CONCLUSIONS

Initiating a structured PLM from the early stages of patients' preparation for RYGB could enhance and extend the benefits of weight loss and positively impact micronutrient (vitamin D, phosphorus, and folic acid) status in obese patients.

Within-limb variation in skin pigmentation does not influence cutaneous vasodilation

Ultraviolet radiation (UVR) exposure acutely reduces nitric oxide (NO)-dependent cutaneous vasodilation. In addition, increased constitutive skin melanin is associated with attenuated NO-dependent cutaneous vasodilation. However, the impact of within-limb variation in skin melanization, associated with seasonal UVR exposure, on NO-dependent cutaneous vasodilation is unknown. We investigated the effect of within-limb variation in skin melanin on NO-dependent cutaneous vasodilation. Intradermal microdialysis fibers were placed in the inner-upper arm, ventral forearm, and dorsal forearm of seven adults (33 ± 14 yr; 4 M/3 F) with constitutively light skin pigmentation. Melanin-index (M-index; an index of skin pigmentation), measured via reflectance spectrophotometry, confirmed differences in sun exposure among sites. A standardized local heating (42°C) protocol induced cutaneous vasodilation. After attaining a stable elevated blood flow plateau, 15 mM NG-nitro-l-arginine methyl ester (l-NAME; NO synthase inhibitor) was infused to quantify the NO contribution. Laser-Doppler flowmetry (LDF) measured red cell flux and cutaneous vascular conductance (CVC = LDF/mean arterial pressure) and was normalized to maximal (%CVCmax; 28 mM sodium nitroprusside + 43°C local heating). Dorsal forearm M-index was higher [50.5 ± 11.8 au (arbitrary units)] compared with the ventral forearm (37.5 ± 7.4 au; P ≤ 0.03) and upper arm (30.0 ± 4.0 au; P ≤ 0.001) M-index. Cutaneous vasodilation responses to local heating were not different among sites (P ≥ 0.12). Importantly, neither the magnitude of the local heating plateau (dorsal: 85 ± 21%; ventral: 70 ± 21%; upper: 87 ± 15%; P ≥ 0.16) nor the NO-mediated component of that response (dorsal: 59 ± 15%; ventral: 54 ± 13%; upper: 55 ± 11%; P ≥ 0.79) was different among sites. These data suggest that within-limb differences in skin pigmentation secondary to seasonal UVR exposure do not alter NO-dependent cutaneous vasodilation.NEW & NOTEWORTHY Locally derived endothelial nitric oxide (NO) contributes to the full expression of cutaneous vasodilation responses. Acute ultraviolet radiation (UVR) exposure attenuates NO-mediated vasodilation of the cutaneous microvasculature. Our findings suggest that in constitutively lightly pigmented skin, variation in skin melanin due to seasonal exposure to UVR does not alter the NO contribution to cutaneous vasodilation. Seasonal UVR exposure does not impact the NO-mediated cutaneous microvascular function.

Difference in Levels of Vitamin D between Indoor and Outdoor Athletes: A Systematic Review and Meta-Analysis

Vitamin D, its importance in different processes taking place in the human body, the effects of abnormal levels of this hormone, either too low or too high, and the need for supplementation have been extensively researched thus far. Variances in exposure to sunlight can cause vitamin D levels to fluctuate. Indoor activity can be a factor for these fluctuations and can lead to a decrease in vitamin D levels. We conducted a systematic review and meta-analysis aiming to identify whether indoor compared to outdoor training has a significant influence on vitamin D levels; we also performed subgroup analyses and multivariate meta-regression. The type of training has an impact on vitamin D levels that is influenced by multiple cofounders. In a subgroup analysis not considering cofounders, the mean serum vitamin D was 3.73 ng/mL higher in outdoor athletes, a difference which barely fails to achieve significance (p = 0.052, a total sample size of 5150). The indoor-outdoor difference is only significant (clinically and statistically) when considering studies performed exclusively on Asian athletes (a mean difference of 9.85 ng/mL, p < 0.01, and a total sample size of 303). When performing the analyses within each season, no significant differences are observed between indoor and outdoor athletes. To control for multiple cofounders (the season, latitude, and Asian/Caucasian race) simultaneously, we constructed a multivariate meta-regression model, which estimated a serum vitamin D concentration lower by 4.446 ng/mL in indoor athletes. While a multivariate model suggests that outdoor training is associated with slightly higher vitamin D concentrations when controlling for the season, latitude, and Asian/Caucasian race, the type of training has a numerically and clinically small impact. This suggests that vitamin D levels and the need for supplementation should not be decided based on training type alone.

Comparative Transcriptome Profiles of Human HaCaT Cells in Response to Gynostemma pentaphyllum Extracts Obtained Using Three Independent Methods by RNA Sequencing

Gynostemma pentaphyllum (GP) is widely used in herbal medicine. In this study, we developed a method for the large-scale production of GP cells using plant tissue culture techniques combined with bioreactors. Six metabolites (uridine, adenosine, guanosine, tyrosine, phenylalanine, and tryptophan) were identified in GP extracts. Transcriptome analyses of HaCaT cells treated with GP extracts using three independent methods were conducted. Most differentially expressed genes (DEGs) from the GP-all condition (combination of three GP extracts) showed similar gene expression on treatment with the three individual GP extracts. The most significantly upregulated gene was LTBP1. Additionally, 125 and 51 genes were upregulated and downregulated, respectively, in response to the GP extracts. The upregulated genes were associated with the response to growth factors and heart development. Some of these genes encode components of elastic fibers and the extracellular matrix and are associated with many cancers. Genes related to folate biosynthesis and vitamin D metabolism were also upregulated. In contrast, many downregulated genes were associated with cell adhesion. Moreover, many DEGs were targeted to the synaptic and neuronal projections. Our study has revealed the functional mechanisms of GP extracts' anti-aging and photoprotective effects on the skin using RNA sequencing.

Vitamin D and risk of hypertension among Black women

Evidence of an association between plasma 25-hydroxyvitamin D [25(OH)D] levels and risk of hypertension, predominantly from studies of White individuals, suggests an inverse relationship. Limited data are available on Black individuals, who are more likely to have vitamin D deficiency. In the Black Women's Health Study (BWHS), a prospective study of 59 000 self-identified Black women from across the US, we assessed levels of a validated predicted vitamin D score in relation to incident hypertension. We followed 42 239 participants who were free of cardiovascular disease and cancer from 1995 to 2019, during which time 19 505 incident cases of hypertension were identified. Cox proportional hazards model were used to calculate multivariable-adjusted hazard ratios (HRs) and 95% confidence intervals (CIs) for the association of predicted vitamin D with the risk of incident hypertension. In age-adjusted analyses, there was a strong inverse dose-response association between predicted vitamin D score and hypertension risk, with an HR of .66 (95% CI: .63-.68, p trend < .0001) for the highest quartile of predicted vitamin D relative to the lowest. After control for potential confounders including body mass index, physical activity, and cigarette smoking, the HR was attenuated to .91 (95% CI: .87-.95, p trend = .002). In this prospective cohort study of Black women, predicted vitamin D score was weakly inversely associated with the incidence of hypertension. This observed association may reflect an inability to fully control for confounding factors.

Skin pigmentation is negatively associated with circulating vitamin D concentration and cutaneous microvascular endothelial function

Darkly pigmented individuals are at the greatest risk of hypovitaminosis D, which may result in microvascular endothelial dysfunction via reduced nitric oxide (NO) bioavailability and/or increased oxidative stress and inflammation. We investigated the associations among skin pigmentation (M-index; skin reflectance spectrophotometry), serum vitamin D concentration [25(OH)D], circulating inflammatory cytokine (TNF-α, IL-6, and IL-10) concentrations, and the NO contribution to local heating-induced cutaneous vasodilation (%NO-mediated vasodilation) in a diversely pigmented cohort of young adults. An intradermal microdialysis fiber was placed in the forearms of 33 healthy adults (14 men/19 women; 18-27 yr; M-index, 30-81 AU) for local delivery of pharmacological agents. Lactated Ringer's solution was perfused through the fiber during local heating-induced (39°C) cutaneous vasodilation. After attaining stable elevated blood flow, 15 mM NG-nitro-l-arginine methyl ester (l-NAME; NO synthase inhibiter) was infused to quantify %NO-mediated vasodilation. Red cell flux was measured (laser-Doppler flowmetry; LDF) and cutaneous vascular conductance (CVC = LDF/MAP) was normalized to maximal (%CVCmax; 28 mM sodium nitroprusside + 43°C). Serum [25(OH)D] and circulating cytokines were analyzed by ELISA and multiplex assay, respectively. M-index was negatively associated with [25(OH)D] (r = -0.57, P < 0.0001) and %NO-mediated vasodilation (r = -0.42, P = 0.02). Serum[25(OH)D] was positively related to %NO (r = 0.41, P = 0.02). Controlling for [25(OH)D] weakened the association between M-index and %NO-mediated dilation (P = 0.16, r = -0.26). There was a negative curvilinear relation between [25(OH)D] and circulating IL-6 (r = -0.56, P < 0.001), but not TNF-α or IL-10 (P ≥ 0.14). IL-6 was not associated with %NO-mediated vasodilation (P = 0.44). These data suggest that vitamin D insufficiency/deficiency may contribute to reduced microvascular endothelial function in healthy, darkly pigmented young adults.NEW & NOTEWORTHY Endothelial dysfunction, an antecedent to hypertension and overt CVD, is commonly observed in otherwise healthy Black adults, although the underlying causes remain unclear. We show that reduced vitamin D availability with increasing degrees of skin pigmentation is associated with reduced microvascular endothelial function, independent of race or ethnicity, in healthy young adults. Greater prevalence of vitamin D deficiency in more darkly pigmented individuals may predispose them to increased risk of endothelial dysfunction.

Skin pigmentation and vitamin D-folate interactions in vascular function: an update

PURPOSE OF REVIEW

Vitamin D and folate promote vascular endothelial health and may therefore help mitigate the development of cardiovascular disease (CVD). Ultraviolet radiation (UVR) exposure stimulates cutaneous vitamin D synthesis but degrades the bioactive metabolite of folate, 5-methyltetrahydrofolate (5-MTHF). Skin melanin absorbs UVR, thereby modulating the impact of UVR exposure on vitamin D and 5-MTHF metabolism. This review presents recent findings regarding the inter-relations among UVR, skin pigmentation, folate and vitamin D, and endothelial function.

RECENT FINDINGS

Evidence for roles of folic acid or vitamin D supplementation on CVD endpoints is inconsistent, although preclinical and clinical studies have demonstrated the efficacy of both micronutrients for improving endothelial function. Vitamin D deficiency is most prevalent in darkly pigmented individuals living in relatively low-UVR environments. Conversely, there is a negative relation between accumulated UVR exposure and serum folate concentration in lightly pigmented adults. The interactions among UVR and bioavailable folate and vitamin D differentially impact endothelial function in differently pigmented skin.

SUMMARY

UVR exposure disparately impacts folate and vitamin D metabolism in differently pigmented skin depending upon regional UVR intensity and seasonality. These findings present new clinical research questions regarding the interactions among UVR, skin pigmentation, folate and vitamin D bioavailability, and endothelial health.

Biophysical evidence to support and extend the vitamin D-folate hypothesis as a paradigm for the evolution of human skin pigmentation

OBJECTIVE

To test the "vitamin D-folate hypothesis for the evolution of human skin pigmentation."

METHODS

Total ozone mapping spectrometer (TOMS) satellite data were used to examine surface UV-irradiance in a large (n = 649) Australian cross-sectional study population. Genetic analysis was used to score vitamin D- and folate-related gene polymorphisms (n = 22), along with two pigmentation gene variants (IRF4-rs12203592/HERC2-rs12913832). Red cell folate and vitamin D₃ were measured by immunoassay and HPLC, respectively.

RESULTS

Ultraviolet radiation (UVR) and pigmentation genes interact to modify blood vitamin levels; Light skin IRF4-TT genotype has greatest folate loss while light skin HERC2-GG genotype has greatest vitamin D₃ synthesis (reflected in both TOMS and seasonal data). UV-wavelength exhibits a dose-response relationship in folate loss within light skin IRF4-TT genotype (305 > 310 > 324 > 380 nm). Significant vitamin D₃ photosynthesis only occurs within light skin HERC2-GG genotype, and is maximal at 305 nm. Three dietary antioxidants (vitamins C, E, and β-carotene) interact with UVR and pigmentation genes preventing oxidative loss of labile reduced folate vitamers, with greatest benefit in light skin IRF4-TT subjects. The putative photosensitiser, riboflavin, did not sensitize red cell folate to UVR and actually afforded protection. Four genes (5xSNPs) influenced blood vitamin levels when stratified by pigmentation genotype; MTHFR-rs1801133/rs1801131, TS-rs34489327, CYP24A-rs17216707, and VDR-ApaI-rs7975232. Lightest IRF4-TT/darkest HERC2-AA genotype combination (greatest folate loss/lowest vitamin D₃ synthesis) has 0% occurrence. The opposing, commonest (39%) compound genotype (darkest IRF4-CC/lightest HERC2-GG) permits least folate loss and greatest synthesis of vitamin D₃ .

CONCLUSION

New biophysical evidence supports the vitamin D-folate hypothesis for evolution of skin pigmentation.

The evolution of human skin pigmentation involved the interactions of genetic, environmental, and cultural variables

The primary biological role of human skin pigmentation is as a mediator of penetration of ultraviolet radiation (UVR) into the deep layers of skin and the cutaneous circulation. Since the origin of Homo sapiens, dark, protective constitutive pigmentation and strong tanning abilities have been favored under conditions of high UVR and represent the baseline condition for modern humans. The evolution of partly depigmented skin and variable tanning abilities has occurred multiple times in prehistory, as populations have dispersed into environments with lower and more seasonal UVR regimes, with unique complements of genes and cultural practices. The evolution of extremes of dark pigmentation and depigmentation has been rare and occurred only under conditions of extremely high or low environmental UVR, promoted by positive selection on variant pigmentation genes followed by limited gene flow. Over time, the evolution of human skin pigmentation has been influenced by the nature and course of human dispersals and modifications of cultural practices, which have modified the nature and actions of skin pigmentation genes. Throughout most of prehistory and history, the evolution of human skin pigmentation has been a contingent and non-deterministic process.

Dissecting dynamics and differences of selective pressures in the evolution of human pigmentation

Human pigmentation is a highly diverse and complex trait among populations and has drawn particular attention from both academic and non-academic investigators for thousands of years. Previous studies detected selection signals in several human pigmentation genes, but few studies have integrated contribution from multiple genes to the evolution of human pigmentation. Moreover, none has quantified selective pressures on human pigmentation over epochs and between populations. Here, we dissect dynamics and differences of selective pressures during different periods and between distinct populations with new approaches. We use genotype data of 19 genes associated with human pigmentation from 17 publicly available datasets and obtain data for 2346 individuals of six representative population groups from across the world. Our results quantify the strength of natural selection on light pigmentation not only in modern Europeans (0.0259/generation) but also in proto-Eurasians (0.00650/generation). Our results also suggest that several derived alleles associated with human dark pigmentation may be under positive directional selection in some African populations. Our study provides the first attempt to quantitatively investigate the dynamics of selective pressures during different time periods in the evolution of human pigmentation.This article has an associated First Person interview with the first author of the article.

Examining "race" in physiology

Racial disparities in cardiovascular and cerebrovascular health outcomes are well described, and recent research has shed light on the mechanistic underpinnings of those disparities. However, "race" is a social construct that is poorly defined and continually evolving and is historically based on faulty premises. The continued categorization by race in physiological research suggests that there are inherent differences between races, rather than addressing the specific underlying factors that result in health disparities between groups. The purpose of this Perspectives article is to provide a brief history of the genesis of categorization by race, why such categorization should be reconsidered in physiology research, and offer recommendations to more directly investigate the underlying factors that result in group disparities in cardiovascular and cerebrovascular health.