Evidence of a Causal Relationship Between Vitamin D Status and Risk of Psoriasis From the UK Biobank Study

The Effect of Phototherapy on Systemic Inflammation Measured with Serum Vitamin D-Binding Protein and hsCRP in Patients with Inflammatory Skin Disease

Vitamin D plays a role in inflammatory skin disease, but the exact mechanisms and the clinical significance remain unclear. According to the free hormone hypothesis, it is the free concentration of 25-hydroxy vitamin D (25(OH)D) that is biologically active. Vitamin D-binding protein (DBP) acts as the major transporter of vitamin D in the circulation, and DBP concentration defines the free 25(OH)D levels. DBP levels are elevated in various inflammatory conditions, including psoriasis. Narrowband-ultraviolet B (NB-UVB) is the most widely used phototherapy and is an established first-line treatment for psoriasis and atopic dermatitis (AD), often used before proceeding to systemic treatment. The aim of this study was to investigate the influence of NB-UVB phototherapy on DBP and high-sensitivity C-reactive protein (hsCRP) levels, as markers of systemic inflammation, in inflammatory skin disease. Thirty adults (psoriasis (n = 20) and AD (n = 10)) were treated with NB-UVB. Serum DBP, hsCRP, total and free 25(OH)D, and 1,25-dihydroxy vitamin D (1,25(OH)2D) were measured before and after NB-UVB. Disease severity was assessed with Psoriasis Area and Severity Index (PASI), SCORing Atopic Dermatitis (SCORAD), and Visual Analogue Scale (VAS). DBP decreased in psoriasis patients and varied with no clear trend in AD patients. HsCRP decreased in both groups, but this did not reach statistical significance. PASI, SCORAD, and VAS improved, and vitamin D levels increased after NB-UVB. Sub-analysis indicated a better response to NB-UVB for patients with vitamin D deficiency and insufficiency compared to vitamin D-sufficient patients. The decrease in DBP after NB-UVB in psoriasis patients suggests a potential systemic anti-inflammatory effect of phototherapy. Measurement of vitamin D levels may potentially serve as a tool to identify patients who would derive the greatest benefit from NB-UVB phototherapy.

No causal relationship between serum vitamin D levels and alcoholic liver disease: a two-sample bidirectional Mendelian randomization study

Background

Numerous observational studies have presented an association between Vitamin D (VD) and Alcoholic Liver Disease (ALD). However, sufficient evidence from Randomized Controlled Trials (RCTs) substantiating this correlation is scarce, thus leaving the causality of this relationship ambiguous. To overcome the shortcomings of traditional observational studies, we performed a two-sample bidirectional Mendelian randomization (MR) analysis to ascertain the causal relationship between VD and ALD.

Methods

We utilized summary statistics datasets from Genome-Wide Association Studies (GWAS) for VD and ALD. We selected genetic instruments that measure circulating VD levels (n = 64,979), and retrieved ALD statistics from GWASs, inclusive of 1,416 cases and 217,376 healthy controls, while excluding chronic liver diseases such as nonalcoholic fatty liver disease, toxic liver disease, and viral hepatitis. Subsequent, MR analyses were performed to obtain effect estimates using inverse variance weighted (IVW) random effect models. Cochran's Q statistic and MR-Egger regression intercept analyses were used to assess pleiotropy. Sensitivity analyses using the MR Egger, weighted median, simple mode, and weighted mode methods were also performed. Leave-one-out analysis was used to identify SNPs with potential effect. Reverse MR analysis was also performed.

Results

In IVW, our MR analysis incorporated 21 independent SNPs, circulating VD levels had no causal effect on ALD [OR = 0.624 (0.336-1.160), p = 0.136] and ALD had no causal effect on circulating VD [OR = 0.997 (0.986-1.008), p = 0.555]. No heterogeneity or pleiotropy was observed (p > 0.05). Other MR methods also agreed with IVW results.

Conclusion

This study provides the causal relationship between genetically predicted circulating Vitamin D levels and ALD and provides new insights into the genetics of ALD.

Vitamin D and human health: evidence from Mendelian randomization studies

We summarized the current evidence on vitamin D and major health outcomes from Mendelian randomization (MR) studies. PubMed and Embase were searched for original MR studies on vitamin D in relation to any health outcome from inception to September 1, 2022. Nonlinear MR findings were excluded due to concerns about the validity of the statistical methods used. A meta-analysis was preformed to synthesize study-specific estimates after excluding overlapping samples, where applicable. The methodological quality of the included studies was evaluated according to the STROBE-MR checklist. A total of 133 MR publications were eligible for inclusion in the analyses. The causal association between vitamin D status and 275 individual outcomes was examined. Linear MR analyses showed genetically high 25-hydroxyvitamin D (25(OH)D) concentrations were associated with reduced risk of multiple sclerosis incidence and relapse, non-infectious uveitis and scleritis, psoriasis, femur fracture, leg fracture, amyotrophic lateral sclerosis, anorexia nervosa, delirium, heart failure, ovarian cancer, non-alcoholic fatty liver disease, dyslipidemia, and bacterial pneumonia, but increased risk of Behçet's disease, Graves' disease, kidney stone disease, fracture of radium/ulna, basal cell carcinoma, and overall cataracts. Stratified analyses showed that the inverse association between genetically predisposed 25(OH)D concentrations and multiple sclerosis risk was significant and consistent regardless of the genetic instruments GIs selected. However, the associations with most of the other outcomes were only pronounced when using genetic variants not limited to those in the vitamin D pathway as GIs. The methodological quality of the included MR studies was substantially heterogeneous. Current evidence from linear MR studies strongly supports a causal role of vitamin D in the development of multiple sclerosis. Suggestive support for a number of other health conditions could help prioritize conditions where vitamin D may be beneficial or harmful.

The association between serum 25-hydroxyvitamin D levels and psoriasis in a large population-based cohort: a cross-sectional analysis of The Tromsø Study 2015-16

BACKGROUND

Case-control studies indicate an association between lower serum 25-hydroxyvitamin D [25(OH)D] levels and psoriasis. Data from larger population-based cohorts including mild cases are sparse.

OBJECTIVES

To investigate the association between 25(OH)D and psoriasis in a large population-based cohort, and assess possible effect modification by overweight.

METHODS

Data from the Tromsø Study 2015-16 (Tromsø7), which included 19 520 participants from the general population aged 40-79 years, were subjected to a cross-sectional analysis. We assessed the shapes of the relationships between 25(OH)D and psoriasis using fractional polynomials. Odds ratios (ORs) for lifetime and active psoriasis were estimated using logistic regression. Adjusted models included month of blood sampling, body mass index (BMI), age and sex. Two-way and additive interaction between BMI and 25(OH)D were explored.

RESULTS

From a total of 19 520 participants [10 203 women (52.3%); mean age 56.3 years (SD 10.4); mean 25[OH]D, 63.4 nmol L-1 (SD 21.9)], 2088 (10.7%) reported lifetime psoriasis and 1179 (6.0%) reported active psoriasis the past 12 months. There was no association between 25(OH)D and lifetime psoriasis [OR per 10 nmol L-1 increase in 25(OH)D 1.02, 95% confidence interval (CI) 0.99-1.04]. The relationship between 25(OH)D and active psoriasis was suggested to be nonlinear, but the model was not significant (P = 0.098). There was evidence for a superadditive effect (i.e. larger than the sum of the factors) of BMI > 27.5 kg m-2 and 25(OH)D < 25 nmol L-1 on the odds for active psoriasis (OR 1.92, 95% CI 1.18-3.12), but not for lifetime psoriasis (OR 1.41, 95% CI 0.93-2.15). There was no evidence for two-way interaction between BMI and 25(OH)D.

CONCLUSIONS

This large population-based study found no significant relationship between 25(OH)D and psoriasis. The analysis may have been underpowered to detect a threshold effect in the lower 25(OH)D spectrum. Interaction analysis indicates that high BMI and vitamin D deficiency combined increase the odds of active psoriasis more than the sum of these factors, with an estimated 92% higher odds for active psoriasis in participants with BMI > 27.5 kg m-2 and 25(OH)D < 25 nmol L-1. Providing advice to prevent vitamin D deficiency may be considered in the follow-up of overweight patients with psoriasis.

Disentangling the complexity of psoriasis in the post-genome-wide association era

In recent years, genome-wide association studies (GWAS) have been instrumental in unraveling the genetic architecture of complex diseases, including psoriasis. The application of large-scale GWA studies in psoriasis has illustrated several associated loci that participate in the cutaneous inflammation, however explaining a fraction of the disease heritability. With the advent of high-throughput sequencing technologies and functional genomics approaches, the post-GWAS era aims to unravel the functional mechanisms underlying the inter-individual variability in psoriasis patients. In this review, we present the key advances of psoriasis GWAS in under-represented populations, rare, non-coding and structural variants and epistatic phenomena that orchestrate the interplay between different cell types. We further review the gene-gene and gene-environment interactions contributing to the disease predisposition and development of comorbidities through Mendelian randomization studies and pleiotropic effects of psoriasis-associated loci. We finally examine the holistic approaches conducted in psoriasis through system genetics and state-of-the-art transcriptomic analyses, discussing their potential implication in the expanding field of precision medicine and characterization of comorbidities.

Relationship between genetically proxied vitamin D and psoriasis risk: a Mendelian randomization study

BACKGROUND

Observational research suggests that vitamin D levels affect psoriasis. However, observational studies are prone to potential confounding or reverse causation, which complicates interpreting the data and drawing causal conclusions.

AIM

To apply Mendelian randomization (MR) methods to comprehensively assess a potential association between vitamin D and psoriasis.

METHODS

Genetic variants strongly associated with 25-hydroxyvitamin D (25OHD) in genome-wide association study (GWAS) data from 417 580 and 79 366 individuals from two independent studies served as instrumental variables (used as the discovery and replication datasets, respectively). As the outcome variable, we used GWAS data of psoriasis (13 229 people in the case group, 21 543 in the control group). We used (i) biologically validated genetic instruments, and (ii) polygenic genetic instruments to assess the relationship between genetically proxied vitamin D and psoriasis. We carried out inverse-variance weighted (IVW) MR analyses for the primary analysis. In sensitivity analyses, we used robust MR approaches.

RESULTS

MR analyses of both the discovery and replication datasets did not show an effect of 25OHD on psoriasis. Neither the IVW MR analysis of the biologically validated instruments [discovery dataset: odds ratio (OR) 0.99; 95% confidence interval (CI) 0.88-1.12, P = 0.873; replication dataset: OR 0.98, 95% CI 0.66-1.46, P = 0.930] nor that of the polygenic genetic instruments (discovery dataset: OR 1.00, 95% CI 0.81-1.22, P = 0.973; replication dataset: OR 0.94, 95% CI 0.64-1.38, P = 0.737) revealed an impact of 25OHD on psoriasis.

CONCLUSION

The present MR study did not support the hypothesis that vitamin D levels, measured by 25OHD, affect psoriasis. This study was conducted on Europeans, so the conclusions may not be applicable to all ethnicities.

Effect of Vitamin D Supplementation on Psoriasis Severity in Patients With Lower-Range Serum 25-Hydroxyvitamin D Levels: A Randomized Clinical Trial

Importance

Topical vitamin D analogues are routine treatment for psoriasis, but the effect of oral supplementation has not been established.

Objective

To examine the effect of vitamin D supplementation on psoriasis severity throughout the winter.

Design, Setting, and Participants

This randomized, double-blind placebo-controlled clinical trial with 2 parallel groups was performed through 2 winter seasons (2017 to 2018 and 2018 to 2019). Randomization was computer generated. All participants, health care clinicians, and outcome assessors were masked to group assignment. Each participant was followed for 4 months. The presented analyses were conducted in May 2022. The trial was conducted at the clinical research unit of the University Hospital of North Norway (Tromsø; Norway). Adults from the general population in Tromsø with active plaque psoriasis and 25-hydroxyvitamin D (25[OH]D) levels of less than 24 ng/mL (to convert to nmol/L, multiply by 2.496) were included.

Intervention

Vitamin D (cholecalciferol, 100 000 IU, loading dose, followed by 20 000 IU/week) or placebo for 4 months.

Main outcomes and Measures

Psoriasis Area Severity Index (PASI) (primary outcome), Physician Global Assessment, self-administered PASI, and Dermatology Life Quality Index scores (secondary outcomes).

Results

A total of 122 participants (46 women [37.7%]; mean [SD] age, 53.6 [10.0] years; mean [SD] PASI score, 3.1 [2.0]; mean [SD] serum 25(OH)D, 14.9 [3.9] ng/mL) were included. Of these, 60 (49.2%) were randomized to the vitamin D group and 62 (50.8%) to the placebo group. A total of 120 participants (59 vitamin D [49.2%]/61 placebo [51.8%]) completed the study. By completion, mean (SD) 25(OH)D levels were 29.7 (5.2) ng/mL (vitamin D) and 12.0 (3.8) ng/mL (placebo). There was no significant difference in change in PASI score between the groups (adjusted difference, 0.11; 95% CI, -0.23 to 0.45). There was no significant difference in change in Physician Global Assessment score (adjusted odds ratio, 0.66; 95% CI, 0.27-1.63), self-administered PASI (adjusted difference, -0.60; 95% CI, -1.76 to 0.55) or Dermatology Life Quality Index (adjusted difference, -0.86; 95% CI, -1.9 to 0.19) between the groups. No adverse effects of the intervention were registered.

Conclusion and Relevance

The results of this randomized clinical trial showed that vitamin D supplementation did not affect psoriasis severity. Low baseline severity scores may explain the lack of measurable effect. Levels of 25(OH)D in the intervention group increased to a less-than-expected degree based on previous experimental data from the same source population, and this may have affected the results.

Trial Registration

ClinicalTrials.gov Identifier: NCT03334136.

Mendelian Randomization Studies in Psoriasis and Psoriatic Arthritis: A Systematic Review

Psoriasis (PSO) and psoriatic arthritis (PSA) are inflammatory diseases with complex genetic and environmental contributions. Although studies have identified environmental and clinical associations with PSO/PSA, causality is difficult to establish. Mendelian randomization (MR) employs the random assortment of genetic alleles at birth to evaluate the causal impact of exposures. We systematically reviewed 27 MR studies in PSO/PSA examining health behaviors, comorbidities, and biomarkers. Exposures, including smoking, obesity, cardiovascular disease, and Crohn's disease, were causal for PSO and PSA, whereas PSO was causally associated with several comorbidities. These findings provide insights that can guide preventive counseling and precision medicine.

Causal Associations between Vitamin D Levels and Psoriasis, Atopic Dermatitis, and Vitiligo: A Bidirectional Two-Sample Mendelian Randomization Analysis

BACKGROUND

Vitamin D level has been reported to be associated with psoriasis, atopic dermatitis, and vitiligo. However, its causal relationship with the risk of these three diseases remains unclear.

METHODS

We obtained genome-wide association statistics for three measures of circulating vitamin D levels (25(OH)D in 120,618 individuals, and 25(OH)D3 and epimeric form C3-epi-25(OH)D3 in 40,562 individuals) and for the diseases psoriasis (3871 cases and 333,288 controls), atopic dermatitis (21,399 cases and 95,464 controls), and vitiligo (4680 cases and 39,586 controls). We performed Mendelian randomization using inverse-variance weighted, weighted median, MR-Egger, and MR-pleiotropy residual sum and outlier methods. We carried out sensitivity analyses to evaluate the robustness of the results.

RESULTS

We showed that elevated vitamin D levels protected individuals from developing psoriasis (OR = 0.995, p = 8.84 × 10-4 for 25(OH)D; OR = 0.997, p = 1.81 × 10-3 for 25(OH)D3; and OR = 0.998, p = 0.044 for C3-epi-25(OH)D3). Genetically predicted risk of atopic dermatitis increased the levels of 25(OH)D (OR = 1.040, p = 7.14 × 10-4) and 25(OH)D3 (OR = 1.208, p = 0.048). A sensitivity analysis suggested the robustness of these causal associations.

CONCLUSIONS

This study reported causal relationships between circulating vitamin D levels and the risk of psoriasis, atopic dermatitis, and vitiligo. These findings provide potential disease intervention and monitoring targets.