Advertisement

Vitamin A is not associated with exacerbations in multiple sclerosis

Open AccessPublished:July 29, 2013DOI:https://doi.org/10.1016/j.msard.2013.06.011

      Highlights

      • Vitamin A inhibits Th17 cells formation and promotes Treg formation.
      • It can therefore be hypothesized to be involved in MS relapse risk.
      • We performed a case-control study and a prospective longitudinal study in RRMS patients.
      • All-trans-retinol levels were not significantly lower in patients, and were not associated with relapse risk.

      Abstract

      Background

      Vitamin A is a multifunctional vitamin that can inhibit the formation of Th17 cells, which are probably involved in the development of relapses in MS. Furthermore, it promotes Treg formation. Therefore, vitamin A can be hypothesized to be lower in patients than in healthy controls, and to decrease relapse risk in relapsing–remitting MS (RRMS) patients.

      Objective

      To compare vitamin A levels in MS patients and controls, and to investigate whether vitamin A levels are associated with relapse risk.

      Methods

      In a case-control study all-trans-retinol levels were compared between 31 RRMS patients and 29 matched controls.
      In a prospective longitudinal study in 73 RRMS patients, serum samples for all-trans-retinol measurements were taken every eight weeks. Associations between all-trans-retinol concentrations and relapse rates were calculated using Poisson regression with the individual serum levels as time-dependent variable. Associations between vitamin A and vitamin D were calculated.

      Results

      Mean vitamin A levels were lower in patients (2.16 μmol/l) than in controls (2.44 μmol/l) but with borderline significance (p=0.05). In the longitudinal study, during follow-up (mean 1.7 years), 58 patients experienced a total of 139 relapses. Monthly moving averages of all-trans retinol levels were categorized into tertiles: a low (<2.9 μmol/l), medium (2.9–3.7 μmol/l) and high level (>3.7 μmol/l). Relapse rates were not associated with serum all-trans retinol levels (p>0.2), in univariate nor in multivariate analysis.
      Serum concentrations of all-trans-retinol and 25-OH-vitamin D were positively correlated, although this correlation was weak (r=0.15).

      Conclusion

      We did not find evidence for a role for vitamin A in the disease course of RRMS. We did find an association between vitamin A and D levels in the RRMS patients, possibly explained by dietary products that contain both fat-soluble vitamins.

      Keywords

      1. Introduction

      Vitamin A or retinol is a fat-soluble vitamin with multiple functions, such as those in vision, growth and the normal differentiation of epithelia (
      • Wolf G.
      A history of vitamin A and retinoids.
      ,
      • Hall J.A.
      • et al.
      The role of retinoic acid in tolerance and immunity.
      ). Over the last 2 decades, it has become clear that vitamin A also has important roles in immune functioning, both in immunological tolerance and in adaptive immune responses (
      • Hall J.A.
      • et al.
      The role of retinoic acid in tolerance and immunity.
      ).
      After absorption from food, most vitamin A is stored in the liver, from where it is added to the circulation bound to retinol-binding protein (RBP) (
      • Blomhoff R.
      • Blomhoff H.K.
      Overview of retinoid metabolism and function.
      ,
      • Theodosiou M.
      • et al.
      From carrot to clinic: an overview of the retinoic acid signaling pathway.
      ). Inside the target cells, retinol is oxidized by alcohol dehydrogenase (ADH) into retinal, which can then be oxidized into the active form retinoic acid (RA) by the more selectively expressed retinaldehyde dehydrogenase (RALDH) (
      • Hall J.A.
      • et al.
      The role of retinoic acid in tolerance and immunity.
      ).
      RA is a signaling molecule that can control gene expression, mainly through the activation of nuclear retinoid receptors. There are three subgroups of retinoid receptors: retinoic acid receptors (RARα-γ), retinoid X receptors (RXRα-γ), and retinoic acid orphan receptors (RORα-γ) (
      • Hirahara K.
      • et al.
      Signal transduction pathways and transcriptional regulation in Th17 cell differentiation.
      ). RXR can form heterodimers with other nuclear receptors, such as vitamin D receptor (VDR) (
      • Theodosiou M.
      • et al.
      From carrot to clinic: an overview of the retinoic acid signaling pathway.
      ).
      RA has been shown to inhibit the formation of Th17 cells, which are probably involved in the development of relapses in MS (
      • Steinman L.
      A rush to judgment on Th17.
      ), in vitro (
      • Mucida D.
      • et al.
      Reciprocal TH17 and regulatory T cell differentiation mediated by retinoic acid.
      ) via binding to RARα (
      • Schambach F.
      • et al.
      Activation of retinoic acid receptor-alpha favours regulatory T cell induction at the expense of IL-17-secreting T helper cell differentiation.
      ,
      • Elias K.M.
      • et al.
      Retinoic acid inhibits Th17 polarization and enhances FoxP3 expression through a Stat-3/Stat-5 independent signaling pathway.
      ). It can do so synergistically with 1,25-diOH-vitamin D (
      • Ikeda U.
      • et al.
      1alpha,25-Dihydroxyvitamin D3 and all-trans retinoic acid synergistically inhibit the differentiation and expansion of Th17 cells.
      ). In EAE, a synthetic retinoid could also inhibit Th17 cell differentiation and ameliorate EAE (
      • Klemann C.
      • et al.
      Synthetic retinoid AM80 inhibits Th17 cells and ameliorates experimental autoimmune encephalomyelitis.
      ). Furthermore, RA can promote the formation of anti-inflammatory Treg cells expressing Foxp3 (
      • Coombes J.L.
      • et al.
      A functionally specialized population of mucosal CD103+ DCs induces Foxp3+ regulatory T cells via a TGF-beta and retinoic acid-dependent mechanism.
      ,
      • Mucida D.
      • et al.
      Reciprocal TH17 and regulatory T cell differentiation mediated by retinoic acid.
      ,
      • Schambach F.
      • et al.
      Activation of retinoic acid receptor-alpha favours regulatory T cell induction at the expense of IL-17-secreting T helper cell differentiation.
      ). Recently, it was also found that vitamin A is possibly associated with MS risk (
      • Salzer J.
      • Hallmans G.
      • Nystrom M.
      • Stenlund H.
      • Wadell G.
      • Sundstrom P.
      Vitamin A and systemic inflammation as protective factors in multiple sclerosis.
      ) and MRI outcomes in MS (
      • Loken-Amsrud K.I.
      • et al.
      Retinol levels are associated with magnetic resonance imaging outcomes in multiple sclerosis.
      ).
      Because of the roles described for vitamin A on Th17 and Treg cells, we hypothesized that (1) vitamin A would be lower in MS patients than in healthy controls, and (2) MS patients with higher vitamin A levels would have a lower relapse risk. To investigate this, we performed two studies: a case-control study of vitamin A levels, and a prospective longitudinal study of vitamin A levels in relapsing-remitting MS (RRMS) patients to investigate the association between vitamin A and relapse risk. Because of possible synergistic effects, we also looked at the associations of vitamin A and vitamin D in the longitudinal study.

      2. Patients and methods

      2.1 Case control study on vitamin A and MS

      2.1.1 Patients and controls

      We randomly selected 31 patients with RRMS from our pool of MS patients, subsequently selecting 29 controls matched for age and sex. All controls had signed for informed consent, and all patients were aware that serum would be stored for later use. The Medical Ethical Committee of the Erasmus Medical Center University Hospital approved the use of these materials.

      2.1.2 Measurement of vitamin A

      All-trans retinol was measured because this is the main form of retinol in the circulation (
      • Royal 3rd, W.
      • et al.
      Retinol measurements and retinoid receptor gene expression in patients with multiple sclerosis.
      ,
      • Theodosiou M.
      • et al.
      From carrot to clinic: an overview of the retinoic acid signaling pathway.
      ;

      Tanumihardjo, SA. Biomarkers of vitamin A status: what do they mean? In: World Health Organization. Report: Priorities in the assessment of vitamin A and iron status in populations, Panama City, Panama, 15-17 September 2010, 2012.

      ), and also the best measure of vitamin A status. For analysis of retinol levels, the samples were extracted with hexane and, after evaporation, dissolved in methanol. Retinol levels were measured through reverse-phase high-performance liquid chromatography (HPLC) (column: 150×4.8 mm, Polaris C18A, Waters Alliance HT2795; detector: Waters 2475 [Waters, Milford, MA]), with excitation at 328 nm and detection of emission at 468 nm. The intra-assay variability of retinol measurements was 3.9% and the inter-assay variability was 5.1%.

      2.1.3 Statistical analysis

      Student’s T-test was used to compare mean all-trans retinol levels between RRMS patients and healthy controls. ANOVA was used to adjust for age. p=0.05 (two-sided) was considered the limit of significance in all analyses. All calculations were done using SPSS 20.0 for Windows.

      2.2 Longitudinal study on vitamin A and exacerbations

      2.2.1 Patients

      For the longitudinal study, data and samples were collected in the Rotterdam Study on Exacerbations in MS, a prospective study in patients with relapsing-remitting MS (
      • Buljevac D.
      • et al.
      Prospective study on the relationship between infections and multiple sclerosis exacerbations.
      ). Patients aged 18–55 years could be included in the study if they had clinically definite MS with a relapsing-remitting disease course and at least two exacerbations in the previous 2 years. Patients were excluded from participation if they suffered from another serious disease. All patients signed for informed consent. The study protocol was approved by the Medical Ethical Committee of the Erasmus Medical Center University Hospital.

      2.2.2 Definitions

      Exacerbation was defined as a worsening of existing symptoms or the appearance of new symptoms lasting for more than 24 h after a period of more than 30 days of improvement or stability, if confirmed by neurologic examination (
      • Schumacker G.A.
      • et al.
      Problems of experimental trials of therapy in multiple sclerosis: report by the panel on the evaluation of experimental trials of therapy in multiple sclerosis.
      ). A temporary neurological deterioration associated with fever was not considered to be an exacerbation.
      Because infection is a known risk factor for exacerbations in multiple sclerosis, the ‘at risk period’ around infection was used as a covariate in this study, as described previously (
      • Buljevac D.
      • et al.
      Prospective study on the relationship between infections and multiple sclerosis exacerbations.
      ).

      2.2.3 Visits, samples and measurement of exacerbations

      All patients visited the outpatient clinic of the Erasmus Medical Centre University Hospital regularly every 8 weeks. At every visit, blood samples were taken and disability was measured using the Kurtzke Expanded Disability Status Scale (EDSS) (
      • Kurtzke J.F.
      Rating neurologic impairment in multiple sclerosis: an expanded disability status scale (EDSS).
      ). In the event of a suspected exacerbation or infection, additional visits were arranged within 3 days. Serum samples were stored at −80 °C until serum vitamin A measurement.

      2.2.4 Measurement of vitamin A and vitamin D

      Measurements of all-trans retinol were as described above. To investigate the association between vitamin A and D, we used a RIA method (DiaSorin, USA) using an extraction method, to measure 25-OH-vitamin D levels. The inter-assay variation coefficient at a concentration of 62 nmol/L was 11.6%; at 109 nmol/L it was 10.3%. The respective intra-assay variation coefficients at these levels were 5.7 and 6.6%. Only serum samples taken at the regular eight-weekly visits were used for the measurement of all-trans retinol and 25-OH-vitamin D; samples taken during exacerbation visits were not evaluated.

      2.2.5 Statistical analysis

      To assess the association between individual serum all-trans retinol concentrations and the incidence rate of exacerbations, we split the follow-up time for each patient, which covered a maximum period of 2.3 years, into intervals of one week each. The number of exacerbations was determined for each of these intervals. The individual exacerbation rate was assumed to depend on the mean serum all-trans retinol concentration over the previous 4 weeks. To obtain this mean level, the weekly levels between measurements were determined per individual using interpolated values. These interpolated values were subsequently averaged. During the period of 4 weeks that followed an exacerbation, an individual was not considered to be at risk for another exacerbation. It was decided a priori to categorize the mean serum levels of the 4 preceding weeks into tertiles: low (<2.9 μmol/l), medium (2.9–3.7 μmol/l) and high (>3.7 μmol/l). The relationship between serum all-trans retinol concentrations and the incidence rate of exacerbations was assessed using the Poisson regression models with the mean individual serum levels as a time-dependent variable. In the calculations we used generalized estimating equations with an exchangeable covariance matrix for the subsequent study weeks. The effect of other factors, including gender, age, EDSS, number of exacerbations before study entry and use of interferon-β during the study, was also estimated using a multivariable generalized linear model with a log-link function. Associations between measured vitamin A and vitamin D concentrations, the latter log-transformed to get an approximate normal distribution, were calculated using mixed model regression analysis for repeated measurements. p=0.05 (two-sided) was considered the limit of significance in all analyses. All calculations were done using SPSS 20.0 for Windows.

      3. Results

      3.1 Case control study on vitamin A concentrations and MS

      3.1.1 Patient characteristics

      The baseline characteristics of the 31 patients and 29 controls included are shown in Table 1. We had no information on the use of vitamin supplements of patients and controls. None of the patients were using interferon β at the time of blood sampling, because sampling was done during a clinical workup for therapy advice within our MS center.
      Table 1Characteristics of patients and controls of the case-control study.
      CharacteristicPatientsSDControlsSD
      Sex (f/m)22/724/7
      Age mean (range)35.4 (19–56)10.335.9 (19–56)10.4
      Ethnicity (%)
      White caucasion77.489.7
      Mediterranean16.110.3
      Black6.5
      Disease duration (years) mean (range)4.5 (0–29)5.4

      3.1.2 Serum vitamin A concentrations

      For most patients and controls, serum all-trans retinol concentrations fell within the normal range. None of the patients and none of the controls were vitamin-A deficient. As Fig. 1 shows, all-trans retinol concentrations where somewhat lower in patients than in controls (mean 2.16±0.55 μmol/l vs. 2.44±0.52 μmol/l), but this difference was only borderline significant (p=0.050). Vitamin A depended on age in the case-control study, but not in the longitudinal study. It did not depend on sex. When adjusting for age, there was no significant difference between patients and controls (p=0.070).
      Figure thumbnail gr1
      Fig. 1Serum all-trans retinol concentrations of relapsing-remitting MS patients and healthy controls.

      3.2 Longitudinal study on vitamin A and exacerbations

      3.2.1 Patient characteristics

      73 patients were included in this study. The mean follow-up time of all patients was 1.7 years (range 0.4–2.3). Nine patients had dropped out of the study before the intended completion date, one due to participation in another study, the other eight for unknown reasons. All patients were Dutch Caucasians; their baseline characteristics are shown in Table 2. In addition to the 13 patients who used interferon-β at study entry, 15 started to use interferon-β during follow-up; these 28 patients used interferon-β at some point during an average of 56 weeks. Vitamin supplements were not widely used among the patients: five used vitamin B complex (without vitamin A) and two used multivitamin pills, one of which contained 6 mg of beta-carotene.
      Table 2Characteristics of patients of the longitudinal study at baseline.
      Variable (n=73)Mean (range)Std. deviation
      Age, years39.4 (19–55)9.1
      Disease duration, years5.2 (0–25)4.1
      Disability (EDSS)
      EDSS is a method for quantifying disability in MS, ranging from 0.0 (normal neurological exam) to 10.0 (death due to MS).
      2.5 (0–6.0)1.6
      Exacerbations in previous 2 years2.2 (1–8)1.3
      Variable (n=73)Proportion (%)
      Gender, F/M77/23
      IFN use, N/Y82/18
      a EDSS is a method for quantifying disability in MS, ranging from 0.0 (normal neurological exam) to 10.0 (death due to MS).
      58 patients experienced a total of 139 exacerbations during this study. Median time from inclusion to first exacerbation was 20 weeks. Thirty-three patients had more than one exacerbation; the average exacerbation rate was 1.2 per year (range 0–6.2 per year). Three patients experienced a sixth exacerbation during follow-up.

      3.2.2 Serum vitamin A concentrations

      Serum all-trans retinol concentrations fluctuated considerably, without a seasonal pattern or other clear pattern. Mean serum all-trans retinol concentration was 3.31±1.14 μmol/l. Mean levels varied substantially between patients (Anova: P<0.001). Within patients there was also a considerable variation between measurement occasions. Of the total variation in levels 40% was due to differences between patients while 60% was due to differences within patients.

      3.2.3 Association between serum vitamin A concentrations and exacerbation risk

      Univariate analysis did not show exacerbation rates to be associated with serum all-trans retinol levels (p>0.2).
      As shown previously(

      Runia, T.F., et al., 2012. Lower serum vitamin D levels are associated with a higher relapse risk in multiple sclerosis. Neurology.

      ), infections were associated with the risk of an exacerbation, the exacerbation rate within an “at risk period” being 2.1-fold higher (95% CI 1.6 to 2.8, P<0.001). Also, vitamin D (25-OH-D) serum levels were found to be associated with exacerbation risk. In the multivariate model including 25-OH-D and infections, infections and 25-OH-D were both still related to the exacerbation rate, whereas all-trans retinol was not (Table 3). Adding gender or the use of interferon-β to the model did not alter these results. Also age, EDSS and the number of exacerbations in the 2 year period before entry into the study were not significantly associated with the exacerbation rates (all p>0.18).
      Table 3Association between exacerbation rate and categorized serum all-trans retinol concentrations according to the multivariable analysis including infection and 25-OH-vitamin D concentrations. ARP infection=at risk period for infection.
      Relative exacerbation rate95% CIP-value
      All-trans retinol concentrationsLow <2.9 μmol/l1.20.8–1.80.329
      Overall p-value: 0.489.
      Medium 2.9–3.7 μmol/l1.30.8–1.90.254
      Overall p-value: 0.489.
      High >3.7 μmol/l1 (reference)
      ARP infectionYes1 (reference)
      No0.40.3–0.6<0.001
      25-OH-D concentrationsLow <50 nmol/l2.01.2–3.40.012
      p-value for trend: 0.010.
      Medium 50–100 nmol/l1.30.8–2.20.281
      p-value for trend: 0.010.
      High >100 nmol/l1 (reference)
      a Overall p-value: 0.489.
      b p-value for trend: 0.010.

      3.2.4 Association between vitamin A and vitamin D

      Serum concentrations of all-trans retinol and 25-OH-D had a significant linear correlation. Mixed model regression analysis showed that for every doubling of serum 25-OH-D concentration the mean all-trans retinol level increased by 0.59 μmol/l (P<0.001). The correlation however was weak (r=0.15).

      4. Discussion

      This case-control study shows that vitamin A concentrations are not significantly lower in MS patients than in healthy controls. Our longitudinal study also shows that vitamin A is not associated with relapse risk in MS patients. We also found that vitamin A and vitamin D were associated in a linear manner.
      There are several reasons to hypothesize that vitamin A is involved in MS. In the past, it has been hypothesized that the susceptibility period in multiple sclerosis lies in early childhood (
      • Pugliatti M.
      • et al.
      Evidence of early childhood as the susceptibility period in multiple sclerosis: space-time cluster analysis in a Sardinian population.
      ) and that the element responsible was (a deficiency in) vitamin A (
      • Warren T.R.
      Multiple sclerosis and infants fed on diets deficient in vitamin A or in selenium and vitamin E.
      ). This hypothesis was based mainly on epidemiological evidence, and the mechanisms through which vitamin A deficiency was thought to cause MS were effects on normal CNS myelination and effects on skull and bone growth affecting normal CNS growth. Since knowledge of the functions of vitamin A in immunity has grown in the last decades (
      • Hall J.A.
      • et al.
      The role of retinoic acid in tolerance and immunity.
      ) (inhibiting Th17 cell formation (
      • Mucida D.
      • et al.
      Reciprocal TH17 and regulatory T cell differentiation mediated by retinoic acid.
      ) and promoting Treg formation (
      • Coombes J.L.
      • et al.
      A functionally specialized population of mucosal CD103+ DCs induces Foxp3+ regulatory T cells via a TGF-beta and retinoic acid-dependent mechanism.
      ;
      • Mucida D.
      • et al.
      Reciprocal TH17 and regulatory T cell differentiation mediated by retinoic acid.
      ;
      • Schambach F.
      • et al.
      Activation of retinoic acid receptor-alpha favours regulatory T cell induction at the expense of IL-17-secreting T helper cell differentiation.
      )), the hypothesis that vitamin A might be involved in the development and disease course of MS has become stronger. Recently, it was also found that RXR agonists can stimulate remyelination (
      • Huang J.K.
      • et al.
      Retinoid X receptor gamma signaling accelerates CNS remyelination.
      ). Vitamin A has even been suggested as a (supplementary) treatment option in MS (
      • Royal 3rd, W.
      • et al.
      Retinol measurements and retinoid receptor gene expression in patients with multiple sclerosis.
      ,
      • Klemann C.
      • et al.
      Synthetic retinoid AM80 inhibits Th17 cells and ameliorates experimental autoimmune encephalomyelitis.
      ). However, in the present case-control and longitudinal studies we cannot provide any evidence that vitamin A is really involved in MS.
      In the case-control study, we found somewhat lower retinol concentrations in patients than in controls, but this was not significant. Other studies that addressed this topic had conflicting results. One study also did not find lower levels than in controls (
      • de Bustos F.
      • et al.
      Serum levels of alpha-carotene, beta-carotene, and retinol in patients with multiple sclerosis.
      ). Another study found lower levels in MS patients than in controls (
      • Besler H.T.
      • et al.
      Serum levels of antioxidant vitamins and lipid peroxidation in multiple sclerosis.
      ). Differences with our study were that all patients had a secondary progressive disease course, and that a different technique was used for the measurements (Neeld–Pearson with trifluoroacetic acid instead of HPLC). A third study compared retinol levels in patients and controls, finding significant differences only between subgroups (
      • Royal 3rd, W.
      • et al.
      Retinol measurements and retinoid receptor gene expression in patients with multiple sclerosis.
      ). It should be noted that in that study retinol levels were slightly higher in interferon-β treated patients.
      The borderline significance in our results suggests that our groups might have been too small. On the other hand, as Fig. 1 shows, the mean levels of vitamin A in patients and controls are not far apart, and confidence intervals are wide, suggesting substantial variation within the patient and control group. In our longitudinal study, we also found substantial within-patient variation of retinol levels. We found that vitamin A was also dependent on age, which has been described before by
      • Looker A.C.
      • et al.
      Serum retinol levels of persons aged 4-74 years from three Hispanic groups.
      but was not found by
      • Hallfrisch J.
      • et al.
      Vitamin A and E intakes and plasma concentrations of retinol, beta-carotene, and alpha-tocopherol in men and women of the Baltimore Longitudinal Study of Aging.
      . Because our control group was age- and sex matched, this has not influenced our conclusions.
      In the longitudinal study we found no association between vitamin A and exacerbation rate. One recent study using the same technique for retinol assessment, found an inverse association between new lesion formation on MRI and vitamin A levels (
      • Loken-Amsrud K.I.
      • et al.
      Retinol levels are associated with magnetic resonance imaging outcomes in multiple sclerosis.
      ). We could not confirm an association between vitamin A and clinical disease activity in MS in our study. But although our longitudinal study with its frequent serum sampling provides a robust way of studying this topic, the fact that we found no association does not totally exclude a role for vitamin A in MS relapses. There might be local function or production of RA in the CNS associated with relapses, that cannot be measured systemically, for example by tissue-specific expression of retinoid receptors or retinaldehyde dehydrogenase (RALDH) (
      • Hall J.A.
      • et al.
      The role of retinoic acid in tolerance and immunity.
      ).
      A limitation of our study is that none of the patients in the case-control study used interferon-β. In the longitudinal study, the use of interferon-β did not influence our results. In studies by others on this topic conflicting results have been found: some found a synergistic effect of RA with interferon-β on T suppressor cell augmentation (
      • Qu Z.X.
      • et al.
      All-trans retinoic acid potentiates the ability of interferon beta-1b to augment suppressor cell function in multiple sclerosis.
      ), others found the association between vitamin A and MRI outcomes to be non-significant during interferon-β use (
      • Loken-Amsrud K.I.
      • et al.
      Retinol levels are associated with magnetic resonance imaging outcomes in multiple sclerosis.
      ). We were unable to confirm any of this here.
      We found an association between serum levels of vitamin A and D. Vitamin A can be absorbed from food, but its levels can also be increased via a rise in hepatic production as a result of exposure to light (
      • Pang W.
      • et al.
      The environmental light influences the circulatory levels of retinoic acid and associates with hepatic lipid metabolism.
      ,
      • Mehta B.K.
      New hypotheses on sunlight and the geographic variability of multiple sclerosis prevalence.
      ). Because vitamin D is also a fat-soluble vitamin that can be absorbed from food and can also be synthesized under the influence of sun light, it is not surprising that the concentrations of both vitamins increase and decrease simultaneously. However, we did not find synergistic action in this study: whereas a higher vitamin D level was associated with a lower relapse risk, vitamin A was not.
      For our analyses of retinol levels, we used random serum samples and not fasting samples. This is justified because retinol is derived from hepatic and other body stores and is a good measure of vitamin-A status, unlike retinyl-esters, which are absorbed after a vitamin-A rich meal (
      • Royal 3rd, W.
      • et al.
      Retinol measurements and retinoid receptor gene expression in patients with multiple sclerosis.
      ).
      In recent years, several studies on the relation between vitamin A and MS have been performed, using different techniques and markers, sometimes with conflicting results (
      • de Bustos F.
      • et al.
      Serum levels of alpha-carotene, beta-carotene, and retinol in patients with multiple sclerosis.
      ,
      • Besler H.T.
      • et al.
      Serum levels of antioxidant vitamins and lipid peroxidation in multiple sclerosis.
      ,
      • Royal 3rd, W.
      • et al.
      Retinol measurements and retinoid receptor gene expression in patients with multiple sclerosis.
      ,
      • Munger K.L.
      • Zhang S.M.
      • O’Reilly E.
      • Hernan M.A.
      • Olek M.J.
      • Willett W.C.
      • et al.
      Vitamin D intake and incidence of multiple sclerosis.
      ,
      • Loken-Amsrud K.I.
      • et al.
      Retinol levels are associated with magnetic resonance imaging outcomes in multiple sclerosis.
      ,
      • Salzer J.
      • Hallmans G.
      • Nystrom M.
      • Stenlund H.
      • Wadell G.
      • Sundstrom P.
      Vitamin A and systemic inflammation as protective factors in multiple sclerosis.
      ). Routine measurement of vitamin A and carotenoids is now generally done using high performance liquid chromatography (HPLC). Lately, the use of plasma RBP as a surrogate marker for retinol is increasing. It should be realized that this is only valid in the absence of infection or when adjusted for CRP levels (2012;
      • Salzer J.
      • Hallmans G.
      • Nystrom M.
      • Stenlund H.
      • Wadell G.
      • Sundstrom P.
      Vitamin A and systemic inflammation as protective factors in multiple sclerosis.
      ).
      In conclusion, there are several reasons to hypothesize that vitamin A has a role in the development and disease course of MS. Here we did not observe differences in retinol levels between patients and controls. In addition, in the prospective study on exacerbations, we found no association with disease activity. These results do not feed the perception that vitamin A could be a useful treatment for MS patients (
      • Royal 3rd, W.
      • et al.
      Retinol measurements and retinoid receptor gene expression in patients with multiple sclerosis.
      ,
      • Klemann C.
      • et al.
      Synthetic retinoid AM80 inhibits Th17 cells and ameliorates experimental autoimmune encephalomyelitis.
      ).

      Conflicts of interest

      The authors declare no conflicts of interest.

      Acknowledgment

      All research of ErasMS is supported by the Dutch MS Research Foundation. The Dutch MS Research Foundation had no role in the study design or in the collection, analysis or interpretation of data.

      References

        • Besler H.T.
        • et al.
        Serum levels of antioxidant vitamins and lipid peroxidation in multiple sclerosis.
        Nutr Neurosci. 2002; 5: 215-220
        • Blomhoff R.
        • Blomhoff H.K.
        Overview of retinoid metabolism and function.
        J Neurobiol. 2006; 66: 606-630
        • Buljevac D.
        • et al.
        Prospective study on the relationship between infections and multiple sclerosis exacerbations.
        Brain. 2002; 125: 952-960
        • Coombes J.L.
        • et al.
        A functionally specialized population of mucosal CD103+ DCs induces Foxp3+ regulatory T cells via a TGF-beta and retinoic acid-dependent mechanism.
        Journal of Experimental Medicine. 2007; 204: 1757-1764
        • de Bustos F.
        • et al.
        Serum levels of alpha-carotene, beta-carotene, and retinol in patients with multiple sclerosis.
        Acta Neurologica Belgica. 2000; 100: 41-43
        • Elias K.M.
        • et al.
        Retinoic acid inhibits Th17 polarization and enhances FoxP3 expression through a Stat-3/Stat-5 independent signaling pathway.
        Blood. 2008; 111: 1013-1020
        • Hall J.A.
        • et al.
        The role of retinoic acid in tolerance and immunity.
        Immunity. 2011; 35: 13-22
        • Hallfrisch J.
        • et al.
        Vitamin A and E intakes and plasma concentrations of retinol, beta-carotene, and alpha-tocopherol in men and women of the Baltimore Longitudinal Study of Aging.
        American Journal of Clinical Nutrition. 1994; 60: 176-182
        • Hirahara K.
        • et al.
        Signal transduction pathways and transcriptional regulation in Th17 cell differentiation.
        Cytokine and Growth Factor Reviews. 2010; 21: 425-434
        • Huang J.K.
        • et al.
        Retinoid X receptor gamma signaling accelerates CNS remyelination.
        Nature Neuroscience. 2011; 14: 45-53
        • Ikeda U.
        • et al.
        1alpha,25-Dihydroxyvitamin D3 and all-trans retinoic acid synergistically inhibit the differentiation and expansion of Th17 cells.
        Immunology Letters. 2010; 134: 7-16
        • Klemann C.
        • et al.
        Synthetic retinoid AM80 inhibits Th17 cells and ameliorates experimental autoimmune encephalomyelitis.
        American Journal of Pathology. 2009; 174: 2234-2245
        • Kurtzke J.F.
        Rating neurologic impairment in multiple sclerosis: an expanded disability status scale (EDSS).
        Neurology. 1983; 33: 1444-1452
        • Loken-Amsrud K.I.
        • et al.
        Retinol levels are associated with magnetic resonance imaging outcomes in multiple sclerosis.
        Multiple Sclerosis. 2012;
        • Looker A.C.
        • et al.
        Serum retinol levels of persons aged 4-74 years from three Hispanic groups.
        American Journal of Clinical Nutrition. 1988; 48: 1490-1496
        • Mehta B.K.
        New hypotheses on sunlight and the geographic variability of multiple sclerosis prevalence.
        Journal of the Neurological Sciences. 2010; 292: 5-10
        • Mucida D.
        • et al.
        Reciprocal TH17 and regulatory T cell differentiation mediated by retinoic acid.
        Science. 2007; 317: 256-260
        • Munger K.L.
        • Zhang S.M.
        • O’Reilly E.
        • Hernan M.A.
        • Olek M.J.
        • Willett W.C.
        • et al.
        Vitamin D intake and incidence of multiple sclerosis.
        Neurology. 2004; 62: 60-65
        • Pang W.
        • et al.
        The environmental light influences the circulatory levels of retinoic acid and associates with hepatic lipid metabolism.
        Endocrinology. 2008; 149: 6336-6342
        • Pugliatti M.
        • et al.
        Evidence of early childhood as the susceptibility period in multiple sclerosis: space-time cluster analysis in a Sardinian population.
        American Journal of Epidemiology. 2006; 164: 326-333
        • Qu Z.X.
        • et al.
        All-trans retinoic acid potentiates the ability of interferon beta-1b to augment suppressor cell function in multiple sclerosis.
        Archives of Neurology. 1998; 55: 315-321
        • Royal 3rd, W.
        • et al.
        Retinol measurements and retinoid receptor gene expression in patients with multiple sclerosis.
        Multiple Sclerosis. 2002; 8: 452-458
      1. Runia, T.F., et al., 2012. Lower serum vitamin D levels are associated with a higher relapse risk in multiple sclerosis. Neurology.

        • Salzer J.
        • Hallmans G.
        • Nystrom M.
        • Stenlund H.
        • Wadell G.
        • Sundstrom P.
        Vitamin A and systemic inflammation as protective factors in multiple sclerosis.
        Multiple Sclerosis. 2013; : 18
        • Schambach F.
        • et al.
        Activation of retinoic acid receptor-alpha favours regulatory T cell induction at the expense of IL-17-secreting T helper cell differentiation.
        European Journal of Immunology. 2007; 37: 2396-2399
        • Schumacker G.A.
        • et al.
        Problems of experimental trials of therapy in multiple sclerosis: report by the panel on the evaluation of experimental trials of therapy in multiple sclerosis.
        Annals of the New York Academy of Sciences. 1965; 122: 552-568
        • Steinman L.
        A rush to judgment on Th17.
        Journal of Experimental Medicine. 2008; 205: 1517-1522
      2. Tanumihardjo, SA. Biomarkers of vitamin A status: what do they mean? In: World Health Organization. Report: Priorities in the assessment of vitamin A and iron status in populations, Panama City, Panama, 15-17 September 2010, 2012.

        • Theodosiou M.
        • et al.
        From carrot to clinic: an overview of the retinoic acid signaling pathway.
        Cellular and Molecular Life Sciences. 2010; 67: 1423-1445
        • Warren T.R.
        Multiple sclerosis and infants fed on diets deficient in vitamin A or in selenium and vitamin E.
        Medical Hypotheses. 1982; 8: 443-454
        • Wolf G.
        A history of vitamin A and retinoids.
        FASEB Journal. 1996; 10: 1102-1107