Investigating causality in the association between vitamin D status and self-reported tiredness

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.

Vitamin D and Its Role on the Fatigue Mitigation: A Narrative Review

Vitamin D has historically been associated with bone metabolism. However, over the years, a growing body of evidence has emerged indicating its involvement in various physiological processes that may influence the onset of numerous pathologies (cardiovascular and neurodegenerative diseases, rheumatological diseases, fertility, cancer, diabetes, or a condition of fatigue). This narrative review investigates the current knowledge of the pathophysiological mechanisms underlying fatigue and the ways in which vitamin D is implicated in these processes. Scientific studies in the databases of PubMed, Scopus, and Web of Science were reviewed with a focus on factors that play a role in the genesis of fatigue, where the influence of vitamin D has been clearly demonstrated. The pathogenic factors of fatigue influenced by vitamin D are related to biochemical factors connected to oxidative stress and inflammatory cytokines. A role in the control of the neurotransmitters dopamine and serotonin has also been demonstrated: an imbalance in the relationship between these two neurotransmitters is linked to the genesis of fatigue. Furthermore, vitamin D is implicated in the control of voltage-gated calcium and chloride channels. Although it has been demonstrated that hypovitaminosis D is associated with numerous pathological conditions, current data on the outcomes of correcting hypovitaminosis D are conflicting. This suggests that, despite the significant involvement of vitamin D in regulating mechanisms governing fatigue, other factors could also play a role.

Falsification of the instrumental variable conditions in Mendelian randomization studies in the UK Biobank

Mendelian randomization (MR) is an increasingly popular approach to estimating causal effects. Although the assumptions underlying MR cannot be verified, they imply certain constraints, the instrumental inequalities, which can be used to falsify the MR conditions. However, the instrumental inequalities are rarely applied in MR. We aimed to explore whether the instrumental inequalities could detect violations of the MR conditions in case studies analyzing the effect of commonly studied exposures on coronary artery disease risk.Using 1077 single nucleotide polymorphisms (SNPs), we applied the instrumental inequalities to MR models for the effects of vitamin D concentration, alcohol consumption, C-reactive protein (CRP), triglycerides, high-density lipoprotein (HDL) cholesterol, and low-density lipoprotein (LDL) cholesterol on coronary artery disease in the UK Biobank. For their relevant exposure, we applied the instrumental inequalities to MR models proposing each SNP as an instrument individually, and to MR models proposing unweighted allele scores as an instrument. We did not identify any violations of the MR assumptions when proposing each SNP as an instrument individually. When proposing allele scores as instruments, we detected violations of the MR assumptions for 5 of 6 exposures.Within our setting, this suggests the instrumental inequalities can be useful for identifying violations of the MR conditions when proposing multiple SNPs as instruments, but may be less useful in determining which SNPs are not instruments. This work demonstrates how incorporating the instrumental inequalities into MR analyses can help researchers to identify and mitigate potential bias.

Serum 25-hydroxyvitamin D and cancer-related fatigue: associations and effects on depression, anxiety, functional capacity and health-related quality of Life in breast cancer survivors during adjuvant endocrine therapy

Background

The adjuvant treatment with Aromatase Inhibitor (AI) is considered standard of care for postmenopausal breast cancer (BC) women with hormone receptor-positive (HR +), however, it often causes adverse effects such as cancer-related fatigue (CRF). The high prevalence of vitamin D deficiency in postmenopausal women who start adjuvant AI supports the hypothesis that hypovitaminosis D would be one of the biological explanations for toxicity of AI. This study aimed to identify the relationship between 25-hydroxyvitamin D [25(OH)D] and CRF, and to analyze their associations and effects on depression, anxiety, functional disability, muscle/joint aches and HRQL.

Methods

This prospective study included 89 postmenopausal women diagnosed with HR + early BC in adjuvant endocrine therapy with AI. Anthropometric and body composition assessments were performed, as well as dietary assessments by application of 24-h dietary recall, at three time points, totaling 24 months of follow-up. The women completed the Cervantes Scale (CS), Hospital Anxiety and Depression Scale (HADS) and Health Assessment Questionnaire (HAQ). The CRF was determined from the Functional Assessment of Chronic Illness Therapy-fatigue (FACIT-F). The serum 25(OH)D was determined by electrochemiluminescence, with cut-off point above 75 nmol/L adopted as sufficiency. Generalized Linear Model (GLzM) and Generalized Mixed Model (GMM) analysis were used.

Results

At baseline, 36% (n = 32) of the women presented CRF and 39.3% (n = 35) had 25(OH)D below 75 nmol/L. None of the women reached the Estimated Average Requirements (EAR) of vitamin D. The causality between 25(OH)D and CRF was not significant. Longitudinally, lower levels of 25(OH)D had a negative effect on anxiety (p = 0.020), Menopause and Health (p = 0.033) and Vasomotor scores (p = 0.007). Also, the CRF had a negative effect on anxiety (p = 0.028); depression (p = 0.027); functional disability (p = 0.022); HRQL (p = 0.007); Menopause and Health (p = 0.042), Psychological (p = 0.008) and Couple Relations (p = 0.008) domains; and on Health (p = 0.019) and Aging (p = 0.036) subdomains. Vasomotor subdomain (β = -2.279, p = 0.045) and muscle/joint aches (β = -0.779, p = 0.013) were significant with CRF only at baseline.

Conclusions

This study found negative effect of body adiposity on CRF. Still, the clinical relevance of 25(OH)D and CRF is highlighted, especially that of CRF, considering the consistent impact on several adverse effects reported by BC survivors during adjuvant endocrine therapy.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12885-022-09962-x.

Vitamin D levels in primary care patients: correlations with clinical, seasonal, and quality-of-life parameters

BACKGROUND

The prevalence of vitamin D deficiency varies across countries and few data exist in the adult population in Greece.

OBJECTIVES

To assess vitamin D levels in unselected patients from primary care and to investigate possible correlations with clinical, seasonal, and quality-of-life parameters.

METHODS

In this cross-sectional study, 389 consecutive patients were included. They were grouped according to vitamin D status as vitamin D deficient (<20 ng/mL) and vitamin D sufficient groups (≥20 ng/mL). Demographic, Epworth Sleepiness Scale (ESS), Athens Insomnia Scale (AIS), Beck Depression Inventory (BDI), and Fatigue Severity Scale (FSS) scores were measured and compared between groups.

RESULTS

Vitamin D deficiency (<20 ng/mL) was observed in 50.4% of the cohort. Female gender (76% vs 66%, P = 0.026), obesity (42% vs 26%, P = 0.005), and hypertension (55% vs 43%, P = 0.023) were higher in the vitamin D deficiency group compared with the group without deficiency. After multiparametric adjustments (for age, gender, obesity, comorbidities, and seasonality), hypertension (odds ratio [OR] = 2.338, 95% confidence interval [CI] = 1.257-4.349, P = 0.007), excessive daytime sleepiness (ESS >10; OR = 3.345, 95% CI = 1.124-9.948, P = 0.029), depressive symptoms (BDI >10; OR = 3.769, 95% CI = 0.984-14.443, P = 0.04), and fatigue (FSS >36; OR = 7.157, 95% CI = 0.855-59.877, P = 0.04) showed significant independent associations with vitamin D deficiency in specific subgroups of patients.

CONCLUSION

A large proportion of patients in primary care had vitamin D deficiency, independently associated with hypertension, sleepiness, depressive symptoms, and fatigue. Further research is needed in order to determine the role of vitamin D in these patients.

The effects of vitamin D supplementation on frailty in older adults at risk for falls

Background

Low serum 25-hydroxyvitamin D [25(OH)D] level is associated with a greater risk of frailty, but the effects of daily vitamin D supplementation on frailty are uncertain. This secondary analysis aimed to examine the effects of vitamin D supplementation on frailty using data from the Study To Understand Fall Reduction and Vitamin D in You (STURDY).

Methods

The STURDY trial, a two-stage Bayesian, response-adaptive, randomized controlled trial, enrolled 688 community-dwelling adults aged ≥ 70 years with a low serum 25(OH)D level (10–29 ng/mL) and elevated fall risk. Participants were initially randomized to 200 IU/d (control dose; n = 339) or a higher dose (1000 IU/d, 2000 IU/d, or 4000 IU/d; n = 349) of vitamin D3. Once the 1000 IU/d was selected as the best higher dose, other higher dose groups were reassigned to the 1000 IU/d group and new enrollees were randomized 1:1 to 1000 IU/d or control group. Data were collected at baseline, 3, 12, and 24 months. Frailty phenotype was based on number of the following conditions: unintentional weight loss, exhaustion, slowness, low activity, and weakness (≥ 3 conditions as frail, 1 or 2 as pre-frail, and 0 as robust). Cox proportional hazard models estimated the risk of developing frailty, or improving or worsening frailty status at follow-up. All models were adjusted for demographics, health conditions, and further stratified by baseline serum 25(OH)D level (insufficiency (20–29 ng/mL) vs. deficiency (10–19 ng/mL)).

Results

Among 687 participants (mean age 77.1 ± 5.4, 44% women) with frailty assessment at baseline, 208 (30%) were robust, 402 (59%) were pre-frail, and 77 (11%) were frail. Overall, there was no significant difference in risk of frailty outcomes comparing the pooled higher doses (PHD; ≥ 1000 IU/d) vs. 200 IU/d. When comparing each higher dose vs. 200 IU/d, the 2000 IU/d group had nearly double the risk of worsening frailty status (HR = 1.89, 95% CI: 1.13–3.16), while the 4000 IU/d group had a lower risk of developing frailty (HR = 0.22, 95% CI: 0.05–0.97). There were no significant associations between vitamin D doses and frailty status in the analyses stratified by baseline serum 25(OH)D level.

Conclusions

High dose vitamin D supplementation did not prevent frailty. Significant subgroup findings might be the results of type 1 error.

Trial registration

ClinicalTrials.gov: NCT02166333.

Vitamin D and Multiple Health Outcomes: An Umbrella Review of Observational Studies, Randomized Controlled Trials, and Mendelian Randomization Studies

Observational studies, randomized controlled trials (RCTs), and Mendelian randomization (MR) studies have yielded inconsistent results on the associations of vitamin D concentrations with multiple health outcomes. In the present umbrella review we aimed to evaluate the effects of low vitamin D concentrations and vitamin D supplementation on multiple health outcomes. We summarized current evidence obtained from meta-analyses of observational studies that examined associations between vitamin D concentrations and multiple health outcomes, meta-analyses of RCTs that investigated the effect of vitamin D supplementation on multiple health outcomes, and MR studies that explored the causal associations of vitamin D concentrations with various diseases (international prospective register of systematic reviews PROSPERO registration number CRD42018091434). A total of 296 meta-analyses of observational studies comprising 111 unique outcomes, 139 meta-analyses of RCTs comprising 46 unique outcomes, and 73 MR studies comprising 43 unique outcomes were included in the present umbrella review. Twenty-eight disease outcomes were identified by both meta-analyses of observational studies and MR studies. Seventeen of these reported disease outcomes had consistent results, demonstrating that lower concentrations of vitamin D were associated with a higher risk for all-cause mortality, Alzheimer's disease, hypertension, schizophrenia, and type 2 diabetes. The combinations of consistent evidence obtained by meta-analyses of observational studies and MR studies together with meta-analyses of RCTs showed that vitamin D supplementation was associated with a decreased risk for all-cause mortality but not associated with the risk for Alzheimer's disease, hypertension, schizophrenia, or type 2 diabetes. The results indicated that vitamin D supplementation is a promising strategy with long-term preventive effects on multiple chronic diseases and thus has the potential to decrease all-cause mortality. However, the current vitamin D supplementation strategy might not be an efficient intervention approach for these diseases, suggesting that new strategies are highly needed to improve the intervention outcomes.

Mendelian randomization analysis of the association between human blood cell traits and uterine polyps

Human blood cells (HBCs) play essential roles in multiple biological processes but their roles in development of uterine polyps are unknown. Here we implemented a Mendelian randomization (MR) analysis to investigate the effects of 36 HBC traits on endometrial polyps (EPs) and cervical polyps (CPs). The random-effect inverse-variance weighted method was adopted as standard MR analysis and three additional MR methods (MR-Egger, weighted median, and MR-PRESSO) were used for sensitivity analyses. Genetic instruments of HBC traits was extracted from a large genome-wide association study of 173,480 individuals, while data for EPs and CPs were obtained from the UK Biobank. All samples were Europeans. Using genetic variants as instrumental variables, our study found that both eosinophil count (OR 0.85, 95% CI 0.79-0.93, P = 1.06 × 10^-4) and eosinophil percentage of white cells (OR 0.84, 95% CI 0.77-0.91, P = 2.43 × 10^-5) were associated with decreased risk of EPs. The results were robust in sensitivity analyses and no evidences of horizontal pleiotropy were observed. While we found no significant associations between HBC traits and CPs. Our findings suggested eosinophils might play important roles in the pathogenesis of EPs. Besides, out study provided novel insight into detecting uterine polyps biomarkers using genetic epidemiology approaches.

Fatigue in inflammatory bowel disease: a problematic ailment

PURPOSE OF REVIEW

Fatigue, a protean complaint encompassing both physical, mental exhaustion but also demotivation, has shown to effect quality of life in patients with inflammatory bowel disease (IBD). Here we present a review of the literature as it relates to IBD-associated fatigue. Moreover, we present the common causes attributed to fatigue and present an algorithmic approach to the assessment of fatigue. Finally, we report data regarding potential management strategies for IBD-associated fatigue.

RECENT FINDINGS

Unfortunately, owing to its multidimensional nature and multifactorial causes, patients with IBD may continue to report fatigue despite optimization of disease management, replenishment of nutritional deficiencies, or management of coexistent disorders. Management likely requires a multidisciplinary approach.

SUMMARY

The majority of patients with IBD report fatigue symptoms both in setting of active disease but also during the course of remission. Fatigue is a multidimensional complaints, and management likely requires a multidisciplinary approach. Herein, we present a framework for the management and assessment of fatigue in IBD.

Detecting Shared Genetic Architecture Among Multiple Phenotypes by Hierarchical Clustering of Gene-Level Association Statistics

Emerging large-scale biobanks pairing genotype data with phenotype data present new opportunities to prioritize shared genetic associations across multiple phenotypes for molecular validation. Past research, by our group and others, has shown gene-level tests of association produce biologically interpretable characterization of the genetic architecture of a given phenotype. Here, we present a new method, Ward clustering to identify Internal Node branch length outliers using Gene Scores (WINGS), for identifying shared genetic architecture among multiple phenotypes. The objective of WINGS is to identify groups of phenotypes, or "clusters," sharing a core set of genes enriched for mutations in cases. We validate WINGS using extensive simulation studies and then combine gene-level association tests with WINGS to identify shared genetic architecture among 81 case-control and seven quantitative phenotypes in 349,468 European-ancestry individuals from the UK Biobank. We identify eight prioritized phenotype clusters and recover multiple published gene-level associations within prioritized clusters.

Environmental effects of stratospheric ozone depletion, UV radiation and interactions with climate change: UNEP Environmental Effects Assessment Panel, update 2019

This assessment, by the United Nations Environment Programme (UNEP) Environmental Effects Assessment Panel (EEAP), one of three Panels informing the Parties to the Montreal Protocol, provides an update, since our previous extensive assessment (Photochem. Photobiol. Sci., 2019, 18, 595-828), of recent findings of current and projected interactive environmental effects of ultraviolet (UV) radiation, stratospheric ozone, and climate change. These effects include those on human health, air quality, terrestrial and aquatic ecosystems, biogeochemical cycles, and materials used in construction and other services. The present update evaluates further evidence of the consequences of human activity on climate change that are altering the exposure of organisms and ecosystems to UV radiation. This in turn reveals the interactive effects of many climate change factors with UV radiation that have implications for the atmosphere, feedbacks, contaminant fate and transport, organismal responses, and many outdoor materials including plastics, wood, and fabrics. The universal ratification of the Montreal Protocol, signed by 197 countries, has led to the regulation and phase-out of chemicals that deplete the stratospheric ozone layer. Although this treaty has had unprecedented success in protecting the ozone layer, and hence all life on Earth from damaging UV radiation, it is also making a substantial contribution to reducing climate warming because many of the chemicals under this treaty are greenhouse gases.

The effect of vitamin D supplementation on serum total 25(OH) levels and biochemical markers of skeletal muscles in runners

Background

The beneficial adaptation of skeletal muscle function to strenuous exercise is partially attributable to the improvement of vitamin D status. The present study aimed to evaluate the effects of a 3-week vitamin D supplementation on serum 25(OH)D levels and skeletal muscle biomarkers (i.e. troponin, myoglobin, creatine kinase and lactic dehydrogenase) of endurance runners.

Methods

A double-blind placebo-controlled study design was used and vitamin D supplementation was compared to a non-treatment control group. Twenty-four runners, competitors of the ultra-marathons held during the National Running Championships, were randomly assigned into two groups supplemented with the dose of 2000 IU vitamin D or placebo for three weeks. All subjects participated in three exercise protocols: (a) incremental exercise test (to determine the maximum oxygen uptake and the intensity of eccentric exercise), (b) eccentric exercise before and (c) after two dietary protocols. Venous blood samples were drawn at rest, immediately after the exercise and after 1 h and 24 h of recovery in order to estimate serum 25(OH)D levels, skeletal muscle biomarkers, proinflammatory cytokines and tumor necrosis factor-alpha (TNF-α) levels. A two-way ANOVA was used to test main effects and their interactions and Pearson correlation coefficients were analyzed to determine the effects of inter-variable relationships.

Results

Significant differences between pre- and post-intervention in baseline 25(OH)D levels were observed (34.9 ± 4.7 versus 40.3 ± 4.9 ng/ml, p = 0.02) in supplemented group. A higher post intervention 25(OH)D level was observed after vitamin D diet compared to placebo (40.3 ± 4.9 versus 31.8 ± 4.2 ng/mL, respectively; p < 0.05). The vitamin D supplementation decreased post-exercise (TN max) and 1 h post-exercise troponin (p = 0.004, p = 0.03, respectively), 1 h post-exercise myoglobin concentration (p = 0.01) and TNF-α levels(p < 0.03). 24 h post exercise creatine kinase activity was significantly lower in supplemented group compared to placebo (p < 0.05). A negative correlation was observed between post exercise 25(OH)D levels and myoglobin levels (r = − 0.57; p = 0.05), and 25(OH)D levels and TNFα (r = − 0.58; p = 0.05) in vitamin D supplemented group.

Conclusions

Three weeks of vitamin D supplementation had a positive effect on serum 25(OH)D levels in endurance trained runners and it caused a marked decrease in post-exercise biomarkers levels. We concluded that vitamin D supplementation might play an important role in prevention of skeletal muscle injuries following exercise with eccentric muscle contraction in athletes.

Genome-wide Association Study for Vitamin D Levels Reveals 69 Independent Loci

We aimed to increase our understanding of the genetic determinants of vitamin D levels by undertaking a large-scale genome-wide association study (GWAS) of serum 25 hydroxyvitamin D (25OHD). To do so, we used imputed genotypes from 401,460 white British UK Biobank participants with available 25OHD levels, retaining single-nucleotide polymorphisms (SNPs) with minor allele frequency (MAF) > 0.1% and imputation quality score > 0.3. We performed a linear mixed model GWAS on standardized log-transformed 25OHD, adjusting for age, sex, season of measurement, and vitamin D supplementation. These results were combined with those from a previous GWAS including 42,274 Europeans. In silico functional follow-up of the GWAS results was undertaken to identify enrichment in gene sets, pathways, and expression in tissues, and to investigate the partitioned heritability of 25OHD and its shared heritability with other traits. Using this approach, the SNP heritability of 25OHD was estimated to 16.1%. 138 conditionally independent SNPs were detected (p value < 6.6 × 10-9) among which 53 had MAF < 5%. Single variant association signals mapped to 69 distinct loci, among which 63 were previously unreported. We identified enrichment in hepatic and lipid metabolism gene pathways and enriched expression of the 25OHD genes in liver, skin, and gastrointestinal tissues. We observed partially shared heritability between 25OHD and socio-economic traits, a feature which may be mediated through time spent outdoors. Therefore, through a large 25OHD GWAS, we identified 63 loci that underline the contribution of genes outside the vitamin D canonical metabolic pathway to the genetic architecture of 25OHD.

Multi-ethnic analysis shows genetic risk and environmental predictors interact to influence 25(OH)D concentration and optimal vitamin D intake

25-Hydroxyvitamin D (25(OH)D) concentration is a complex trait with genetic and environmental predictors that may determine how much vitamin D exposure is required to reach optimal concentration. Interactions between continuous measures of a polygenic score (PGS) and vitamin D intake (PGS*intake) or available ultraviolet (UV) radiation (PGS*UV) were evaluated in individuals of African (n = 1,099) or European (n = 8,569) ancestries. Interaction terms and joint effects (main and interaction terms) were tested using one-degree of freedom (1-DF) and 2-DF models, respectively. Models controlled for age, sex, body mass index, cohort, and dietary intake/available UV. In addition, in participants achieving Institute of Medicine (IOM) vitamin D intake recommendations, 25(OH)D was evaluated by level PGS. The 2-DF PGS*intake, 1-DF PGS*UV, and 2-DF PGS*UV results were statistically significant in participants of European ancestry (p = 3.3 × 10-18 , p =  2.1 × 10-2 , and p =  2.4 × 10-19 , respectively), but not in those of African ancestry. In European-ancestry participants reaching IOM vitamin D intake guidelines, the percent of participants achieving adequate 25(OH)D ( >20 ng/ml) increased as genetic risk decreased (72% vs. 89% in highest vs. lowest risk; p = .018). Available UV radiation and vitamin D intake interact with genetics to influence 25(OH)D. Individuals with higher genetic risk may require more vitamin D exposure to maintain optimal 25(OH)D concentrations.

Association between vitamin D and fatigue in patients with rheumatoid arthritis: a cross-sectional study

OBJECTIVES

In rheumatoid arthritis (RA), fatigue is an important complaint with a significant impact on quality of life. Vitamin D has modulatory effects on cells of the immune system and may potentially affect RA disease activity and thereby RA-related fatigue. The purpose of this study was to explore associations between fatigue and vitamin D status in patients with RA.

DESIGN

Hypothesis-generating cross-sectional study.

SETTING

Scheduled follow-up visits at a hospital-based general rheumatology clinic.

PARTICIPANTS

Patients (n=169) with established RA.

PRIMARY OUTCOME MEASURES AND ANLYSES

Fatigue, assessed by the Chalder fatigue questionnaire, and serum concentrations of 25-hydroxyvitamin D (25(OH)D), assessed by liquid chromatography-tandem mass spectrometry. Associations were analysed by correlation, and multivariate linear regression with adjustments for age, sex, body mass index, RA disease activity as measured by the Disease Activity Score 28-joint count C reactive protein (DAS28-CRP), psychological distress, pain and sleep. Fatigue was also compared across four groups based on the levels of serum 25(OH)D with cut points at 30, 50 and 75 nmol/L using one-way analysis of variance.

RESULTS

Two-thirds of the patients (116/169, 69%) were classified with low RA disease activity, that is, a DAS28-CRP score below 3.2. Their mean (SD) serum 25(OH)D concentration was 56.3 (21.2) nmol/L, with 77 (45.6%) having values below 50 nmol/L and 12 patients (7.1%) below 30 nmol/L. The correlation between fatigue and serum concentrations of 25(OH)D was weak and not statistically significant, r = -0.14 (95% CI: -0.29 to 0.03, p=0.08). In the multivariate model, fatigue was significantly associated with RA disease activity, psychological distress and pain, but not with serum 25(OH)D. Fatigue did not differ across groups with varying levels of serum 25(OH)D.

CONCLUSION

This cross-sectional study found no evidence of association between vitamin D and fatigue in patients with RA.

Time trends of vitamin D concentrations in northern Sweden between 1986 and 2014: a population-based cross-sectional study

Purpose

Vitamin D, produced through cutaneous photosynthesis or ingested via foods or supplements, has generated considerable research interest due to its potential health effects. However, epidemiological data on the time trends of vitamin D status are sparse, especially from northern Europe. We examined the time trend of vitamin D concentrations in northern Sweden between 1986 and 2014.

Methods

We used data on 11,129 men and women (aged 25–74 years) from seven population-based surveys (the Northern Sweden MONICA study), recruited between 1986 and 2014. Serum vitamin D (25-hydroxyvitamin D) status was measured using a one-step immunoassay (Abbott Architect). Multivariable linear regression models, adjusted for age, sex, and a number of other variables, were used to estimate the time trend of vitamin D concentrations.

Results

The mean value of vitamin D in the entire study population was 19.9 ng/mL [standard deviation (SD) 7.9], with lower values in men (19.4 ng/mL; SD 7.5) than in women (20.5 ng/mL; SD 8.2). Using the survey in 1986 as reference category, the multivariable-adjusted mean difference [95% confidence interval (CI)] in ng/mL was 2.7 (2.2, 3.3) in 1990, 3.2 (2.7, 3.7) in 1994, 1.6 (1.0, 2.1) in 1999, − 2.0 (− 2.5, − 1.4) in 2004, 1.0 (0.4, 1.5) in 2009, and 3.1 (2.5, 3.6) in 2014.

Conclusion

In this large cross-sectional study, we observed no clear upward or downward trend of vitamin D concentrations in northern Sweden between 1986 and 2014.

Electronic supplementary material

The online version of this article (10.1007/s00394-019-02142-x) contains supplementary material, which is available to authorized users.

Decrease in Serum Vitamin D Level of Older Patients with Fatigue

Fatigue is characterized by reduced energy level, decreased muscle strength, and a variable degree of cognitive impairment. Recent evidences seem to link vitamin D deficiency to fatigue. The aim of this study was to assess and compare vitamin D status in a cohort of older subjects with and without fatigue. We recruited a total of 480 subjects, 240 patients with fatigue and 240 controls without fatigue, from the Cannizzaro Hospital of Catania (Italy). Fatigue severity was measured by the fatigue severity scale, whereas mental and physical fatigue were measured through the Wessely and Powell fatigue scale, respectively. We also measured several blood parameters and 25-OH vitamin D. Subjects with fatigue showed lower levels of vitamin D as compared with those without fatigue. Blood levels of parameters related to fatigue were normal in both groups of subjects, however, platelet, hemoglobin, hematocrit (p < 0.05), mean corpuscular volume, C-reactive protein (CRP), iron, vitamin B12, and folic acid (p < 0.001) were significantly higher in the fatigue group with respect to the control group. Moreover, compared to controls, patients showed higher scores in the physical (p < 0.001), mental (p < 0.001), and severity (p < 0.001) fatigue scales. Finally, vitamin D inversely correlated with fatigue severity (r = -0.428, p < 0.01), whereas creatine kinase and CRP levels did not correlate with vitamin D. In conclusion, our data showed a direct link between vitamin D and fatigue in older subjects, suggesting translational implications in the diagnosis and management of these patients.

Decrease in Serum Vitamin D Level of Older Patients with Fatigue

Fatigue is characterized by reduced energy level, decreased muscle strength, and a variable degree of cognitive impairment. Recent evidences seem to link vitamin D deficiency to fatigue. The aim of this study was to assess and compare vitamin D status in a cohort of older subjects with and without fatigue. We recruited a total of 480 subjects, 240 patients with fatigue and 240 controls without fatigue, from the Cannizzaro Hospital of Catania (Italy). Fatigue severity was measured by the fatigue severity scale, whereas mental and physical fatigue were measured through the Wessely and Powell fatigue scale, respectively. We also measured several blood parameters and 25-OH vitamin D. Subjects with fatigue showed lower levels of vitamin D as compared with those without fatigue. Blood levels of parameters related to fatigue were normal in both groups of subjects, however, platelet, hemoglobin, hematocrit (p < 0.05), mean corpuscular volume, C-reactive protein (CRP), iron, vitamin B12, and folic acid (p < 0.001) were significantly higher in the fatigue group with respect to the control group. Moreover, compared to controls, patients showed higher scores in the physical (p < 0.001), mental (p < 0.001), and severity (p < 0.001) fatigue scales. Finally, vitamin D inversely correlated with fatigue severity (r = -0.428, p < 0.01), whereas creatine kinase and CRP levels did not correlate with vitamin D. In conclusion, our data showed a direct link between vitamin D and fatigue in older subjects, suggesting translational implications in the diagnosis and management of these patients.