Serologic Response to the Epstein-Barr Virus Peptidome and the Risk for Multiple Sclerosis.

Importance: It remains unclear why only a small proportion of individuals infected with the Epstein-Barr virus (EBV) develop multiple sclerosis (MS) and what the underlying mechanisms are. Objective: To assess the serologic response to all EBV peptides before the first symptoms of MS occur, determine whether the disease is associated with a distinct immune response to EBV, and evaluate whether specific EBV epitopes drive this response. Design, Setting, and Participants: In this prospective, nested case-control study, individuals were selected among US military personnel with serum samples stored in the US Department of Defense Serum Repository. Individuals with MS had serum collected at a median 1 year before onset (reported to the military in 2000-2011) and were matched to controls for age, sex, race and ethnicity, blood collection, and military branch. No individuals were excluded. The data were analyzed between September 1, 2022, and August 31, 2023. Exposure: Antibodies (enrichment z scores) to the human virome measured using VirScan (phage-displayed immunoprecipitation and sequencing). Main Outcome and Measure: Rate ratios (RRs) for MS for antibodies to 2263 EBV peptides (the EBV peptidome) were estimated using conditional logistic regression, adjusting for total anti-EBV nuclear antigen 1 (EBNA-1) antibodies, which have consistently been associated with a higher MS risk. The role of antibodies against other viral peptides was also explored. Results: A total of 30 individuals with MS were matched with 30 controls. Mean (SD) age at sample collection was 27.8 (6.5) years; 46 of 60 participants (76.7%) were male. The antibody response to the EBV peptidome was stronger in individuals with MS, but without a discernible pattern. The antibody responses to 66 EBV peptides, the majority mapping to EBNA antigens, were significantly higher in preonset sera from individuals with MS (RR of highest vs lowest tertile of antibody enrichment, 33.4; 95% CI, 2.5-448.4; P for trend = .008). Higher total anti-EBNA-1 antibodies were also associated with an elevated MS risk (top vs bottom tertile: RR, 27.6; 95% CI, 2.3-327.6; P for trend = .008). After adjusting for total anti-EBNA-1 antibodies, risk estimates from most EBV peptides analyses were attenuated, with 4 remaining significantly associated with MS, the strongest within EBNA-6/EBNA-3C, while the association between total anti-EBNA-1 antibodies and MS persisted. Conclusion and Relevance: These findings suggest that antibody response to EBNA-1 may be the strongest serologic risk factor for MS. No single EBV peptide stood out as being selectively targeted in individuals with MS but not controls. Larger investigations are needed to explore possible heterogeneity of anti-EBV humoral immunity in MS.

Smoking and multiple sclerosis risk in black people: A nested case-control study.

BACKGROUND: Smoking is a well-established risk factor for MS; however, it is not known whether its effect on disease risk varies by race/ethnicity. METHODS: We conducted a nested case-control study among US military personnel who have serum samples stored at the Department of Defense Serum Repository. We measured serum cotinine levels, a marker of tobacco smoke exposure, in 157 Black and 23 White individuals who developed MS during follow-up. Controls were randomly selected and matched to each case by age, sex, race/ethnicity, dates of sample collection, and branch of military service. RESULTS: Smoking was not associated with an increased risk of MS in Black people (RR: 1.08, 95 % CI: 0.63-1.85). The results remained similar in analyses restricted to smoking status at baseline, to samples collected 5 years before symptom onset, and using different cut-off levels in cotinine to define smoking status. Smoking was not statistically significantly associated with MS risk in White people, but the point estimate was similar to what has previously been reported in other studies (RR: 1.85, 95 % CI: 0.56-6.16). CONCLUSIONS: Smoking was not associated with MS risk in Black people. Given the consistent association between smoking and MS risk in predominantly White populations, this may suggest that the association between smoking and MS varies by race/ethnicity.

Longitudinal analysis reveals high prevalence of Epstein-Barr virus associated with multiple sclerosis.

Multiple sclerosis (MS) is a chronic inflammatory demyelinating disease of the central nervous system of unknown etiology. We tested the hypothesis that MS is caused by Epstein-Barr virus (EBV) in a cohort comprising more than 10 million young adults on active duty in the US military, 955 of whom were diagnosed with MS during their period of service. Risk of MS increased 32-fold after infection with EBV but was not increased after infection with other viruses, including the similarly transmitted cytomegalovirus. Serum levels of neurofilament light chain, a biomarker of neuroaxonal degeneration, increased only after EBV seroconversion. These findings cannot be explained by any known risk factor for MS and suggest EBV as the leading cause of MS.

Long-term effects of latitude, ambient temperature, and ultraviolet radiation on the incidence of multiple sclerosis in two cohorts of US women.

BACKGROUND: Differences in multiple sclerosis (MS) risk by latitude have been observed worldwide; however, the exposures driving these associations are unknown. Ultraviolet radiation (UV) has been explored as a risk factor, and ambient temperature has been correlated with disease progression. However, no study has examined the impact of all three exposures. We examined the association between these exposures and incidence of MS within two nationwide prospective cohorts of women, the Nurses' Health Study (NHS) and Nurses' Health Study II (NHSII). METHODS: Both cohorts were followed with biennial questionnaires to ascertain new diagnoses and risk factors. Time-varying exposures to latitude, cumulative average July temperature (°C), and cumulative average July erythemal UV (mW/m2) were predicted at each participant's biennially updated residential addresses. Using Cox proportional hazards models adjusted for MS risk factors, we calculated hazard ratios (HR) and 95% confidence intervals (CIs) within each cohort and pooled via meta-analyses. RESULTS: In multivariable models, there were suggestions that decreasing latitude (meta-analysis multivariable-adjusted HR = 0.72; 95% CI 0.55, 0.94 for women living <35.73° compared with those ≥42.15°, P-for-trend = 0.007) and increasing cumulative average July temperature (meta-analysis multivariable-adjusted HR = 0.81; 95% CI 0.72, 0.91 for each interquartile range increase [3.91°]) were associated with decreasing risk of MS. There was no evidence of heterogeneity between cohorts. We did not observe consistent associations with cumulative average UV. CONCLUSION: Our results suggest that adult exposures to decreasing latitude and increasing temperature, but not UV, were associated with reduced MS risk in these two cohorts of women. Studies of MS incidence may want to consider temperature as a risk factor.

Vitamin D, smoking, EBV, and long-term cognitive performance in MS: 11-year follow-up of BENEFIT.

OBJECTIVE: To investigate whether vitamin D, smoking, and anti-Epstein-Barr virus (EBV) antibody concentrations predict long-term cognitive status and neuroaxonal injury in multiple sclerosis (MS). METHODS: This study was conducted among 278 patients with clinically isolated syndrome who participated in the clinical trial BENEFIT (Betaferon/Betaseron in Newly Emerging Multiple Sclerosis for Initial Treatment) and completed the 11-year assessment (BENEFIT-11). We measured serum 25-hydroxyvitamin-D (25(OH)D), cotinine (smoking biomarker), and anti-Epstein-Barr virus nuclear antigen 1 (EBNA-1) immunoglobulin G (IgG) at baseline and at months 6, 12, and 24 and examined whether these biomarkers contributed to predict Paced Auditory Serial Addition Test (PASAT)-3 scores and serum neurofilament light chain (NfL) concentrations at 11 years. Linear and logistic regression models were adjusted for sex, baseline age, treatment allocation, steroid treatment, multifocal symptoms, T2 lesions, and body mass index. RESULTS: Higher vitamin D predicted better, whereas smoking predicted worse cognitive performance. A 50-nmol/L higher mean 25(OH)D in the first 2 years was related to 65% lower odds of poorer PASAT performance at year 11 (95% confidence intervals [95% CIs]: 0.14-0.89). Standardized PASAT scores were lower in smokers and heavy smokers than nonsmokers (p trend = 0.026). Baseline anti-EBNA-1 IgG levels did not predict cognitive performance (p trend = 0.88). Associations with NfL concentrations at year 11 corroborated these findings-a 50-nmol/L higher mean 25(OH)D in the first 2 years was associated with 20% lower NfL (95% CI: -36% to 0%), whereas smokers had 20% higher NfL levels than nonsmokers (95% CI: 2%-40%). Anti-EBNA-1 antibodies were not associated with NfL. CONCLUSIONS: Lower vitamin D and smoking after clinical onset predicted worse long-term cognitive function and neuronal integrity in patients with MS.

Epstein-barr virus and multiple sclerosis risk in the finnish maternity cohort.

OBJECTIVE: To determine whether maternal Epstein-Barr virus (EBV) IgG antibody levels are associated with risk of multiple sclerosis (MS) in the offspring. METHODS: We conducted a prospective nested case-control study in the Finnish Maternity Cohort (FMC) with serum samples from >800,000 women collected during pregnancy since 1983. Cases of MS among offspring born between 1983 and 1991 were identified via hospital and prescription registries; 176 cases were matched to up to 3 controls (n = 326) on region and dates of birth, sample collection, and mother's birth. We used conditional logistic regression to estimate relative risks (RRs) and adjusted models for sex of the child, gestational age at sample collection, and maternal serum 25-hydroxyvitamin D and cotinine levels. Similar analyses were conducted among 1,049 women with MS and 1,867 matched controls in the FMC. RESULTS: Maternal viral capsid antigen IgG levels during pregnancy were associated with an increased MS risk among offspring (RRtop vs bottom quintile = 2.44, 95% confidence interval [CI] = 1.20-5.00, p trend = 0.004); no associations were found between maternal EBV nuclear antigen 1 (EBNA-1), diffuse early antigen, or cytomegalovirus IgG levels and offspring MS risk. Among women in the FMC, those in the highest versus lowest quintile of EBNA-1 IgG levels had a 3-fold higher risk of MS (RR = 3.21, 95% CI = 2.37-4.35, p trend <1.11e-16). These associations were not confounded or modified by 25-hydroxyvitamin D. INTERPRETATION: Offspring of mothers with high viral capsid antigen IgG during pregnancy appear to have an increased risk of MS. The increase in MS risk among women with elevated prediagnostic EBNA-1 IgG levels is consistent with previous results. ANN NEUROL 2019;86:436-442.

Total intake of different minerals and the risk of multiple sclerosis.

OBJECTIVE: To investigate the association between mineral intake (potassium, magnesium, calcium, phosphorus, iron, zinc, manganese, copper) and multiple sclerosis (MS) risk. METHODS: In a prospective cohort study, we assessed dietary and supplemental mineral intake by a validated food frequency questionnaire administered every 4 years to 80,920 nurses in the Nurses' Health Study (1984-2002) and 94,511 in the Nurses' Health Study II (1991-2007). There were 479 new MS cases during follow-up. We estimated hazard ratios and 95% confidence intervals for the association of energy-adjusted mineral intake with MS risk using Cox regression, adjusting for age, residence latitude at age 15, ancestry, body mass index at age 18, supplemental vitamin D, smoking, and total energy intake. RESULTS: We did not find any association between the minerals and MS risk, either for baseline or cumulative intake during follow-up. The associations were null comparing women with highest to those with lowest intakes in quintiles or deciles and there was no significant trend for higher intakes (p trend across baseline quintiles: potassium 0.35, magnesium 0.13, calcium 0.22, phosphorus 0.97, iron 0.85, zinc 0.67, manganese 0.48, copper 0.59). CONCLUSIONS: Our findings suggest that mineral intake is not an important determinant of MS risk.

Diet quality and risk of multiple sclerosis in two cohorts of US women.

OBJECTIVE: To determine the association between measures of overall diet quality (dietary indices/patterns) and risk of multiple sclerosis (MS). METHODS: Over 185,000 women in the Nurses' Health Study (NHS) and Nurses' Health Study II (NHSII) completed semiquantitative food frequency questionnaires every 4 years. There were 480 MS incident cases. Diet quality was assessed using the Alternative Healthy Eating Index-2010 (AHEI-2010), Alternate Mediterranean Diet (aMED) index, and Dietary Approaches to Stop Hypertension (DASH) index. Principal component analysis was used to determine major dietary patterns. We calculated the hazard ratio (HR) of MS with Cox multivariate models adjusted for age, latitude of residence at age 15, body mass index at age 18, supplemental vitamin D intake, and cigarette smoking. RESULTS: None of the dietary indices, AHEI-2010, aMED, or DASH, at baseline was statistically significantly related to the risk of MS. The principal component analysis identified "Western" and "prudent" dietary patterns, neither of which was associated with MS risk (HR, top vs bottom quintile: Western, 0.81 (p = 0.31) and prudent, 0.96 (p = 0.94)). When the analysis was repeated using cumulative average dietary pattern scores, the results were unchanged. CONCLUSION: There was no evidence of an association between overall diet quality and risk of developing MS among women.

Sun exposure over the life course and associations with multiple sclerosis.

OBJECTIVE: To examine sun exposure and multiple sclerosis (MS) over the life course (ages 5-15 and 16-20 years, every 10 years thereafter). METHODS: Cases with MS (n = 151) and age-matched controls (n = 235) from the Nurses' Health Study cohorts completed summer, winter, and lifetime sun exposure history questionnaires. Cumulative ambient ultraviolet (UV)-B (based on latitude, altitude, cloud cover) exposure before MS onset was expressed as tertiles. Seasonal sun exposure was defined as low vs high hours per week (summer [≤9 vs >10 h/wk]; winter [≤3 vs >4 h/wk]). Relative risks (RRs) and 95% confidence intervals (CIs) were estimated via conditional logistic regression with adjustment for body mass index, ancestry, smoking, and vitamin D supplementation. RESULTS: Most participants were white (98%); the mean age at MS onset was 39.5 years. Living in high (vs low) UV-B areas before MS onset was associated with a 45% lower MS risk (adjusted RR 0.55, 95% CI 0.42-0.73). Similar reduced risks (51%-52%) for medium or high exposure were observed at ages 5 to 15 years and at 5 to 15 years before MS onset (adjusted p < 0.05). At age 5 to 15 years, living in a high (vs low) UV-B area and having high (vs low) summer sun exposure were associated with a lower MS risk (RR 0.45, 95% CI 0.21-0.96). CONCLUSION: Living in high ambient UV-B areas during childhood and the years leading up to MS onset was associated with a lower MS risk. High summer sun exposure in high ambient UV-B areas was also associated with a reduced risk.

No association between dietary sodium intake and the risk of multiple sclerosis.

OBJECTIVE: To prospectively investigate the association between dietary sodium intake and multiple sclerosis (MS) risk. METHODS: In this cohort study, we assessed dietary sodium intake by a validated food frequency questionnaire administered every 4 years to 80,920 nurses in the Nurses' Health Study (NHS) (1984-2002) and to 94,511 in the Nurses' Health Study II (NHSII) (1991-2007), and calibrated it using data from a validation study. There were 479 new MS cases during follow-up. We used Cox proportional hazards models to estimate hazard ratios (HR) and 95% confidence intervals (CI) for the effect of energy-adjusted dietary sodium on MS risk, adjusting also for age, latitude of residence at age 15, ancestry, body mass index at age 18, supplemental vitamin D intake, cigarette smoking, and total energy intake in each cohort. The results in both cohorts were pooled using fixed effects models. RESULTS: Total dietary intake of sodium at baseline was not associated with MS risk (highest [medians: 3.2 g/d NHS; 3.5 g/d NHSII] vs lowest [medians: 2.5 g/d NHS; 2.8 g/d NHSII] quintile: HRpooled 0.98, 95% CI 0.74-1.30, p for trend = 0.75). Cumulative average sodium intake during follow-up was also not associated with MS risk (highest [medians: 3.3 g/d NHS; 3.4 g/d NHSII] vs lowest [medians: 2.7 g/d NHS; 2.8 g/d NHSII] quintile: HRpooled 1.02, 95% CI 0.76-1.37, p for trend = 0.76). Comparing more extreme sodium intake in deciles yielded similar results (p for trend = 0.95). CONCLUSIONS: Our findings suggest that higher dietary sodium intake does not increase the risk of developing MS.

Polyunsaturated fatty acids and the risk of multiple sclerosis.

BACKGROUND: Results from previous studies on polyunsaturated fatty acid (PUFA) intake and multiple sclerosis (MS) risk are conflicting. OBJECTIVE: To prospectively investigate the association between dietary intake of PUFA and MS risk. METHODS: We followed 80,920 women from Nurses' Health Study (1984-2004) and 94,511 women from Nurses' Health Study II (1991-2009) who reported on diet using a validated food frequency questionnaire every 4 years and identified 479 incident MS cases during follow-up. We used Cox regression to estimate hazard ratios (HRs) and 95% confidence intervals (CIs), for the effect of PUFA intake on MS risk adjusting for age, latitude of residence at age 15, ancestry, cigarette smoking, supplemental vitamin D intake, body mass index, and total energy intake. RESULTS: Higher intake of total PUFA at baseline was associated with a lower risk of MS (HR top vs bottom quintile: 0.67, 95% CI: 0.49-0.90, p trend = 0.01). Among the specific types of PUFA, only α-linolenic acid (ALA) was inversely associated with MS risk (HR top vs bottom quintile: 0.61, 95% CI: 0.45-0.83, p trend = 0.001). The long-chain fatty acids eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA) were not associated with MS risk. CONCLUSION: Low dietary PUFA intake may be another modifiable risk factor for MS.

Physical activity and the incidence of multiple sclerosis.

OBJECTIVE: To study whether physical activity during adulthood or early life is associated with multiple sclerosis (MS) incidence in 2 prospective cohorts of women. METHODS: Women in the Nurses' Health Study (NHS) (n = 81,723; 1986-2004) and NHS II (n = 111,804; 1989-2009) reported recent physical activity at baseline and in selected follow-up questionnaires. Using this information, we calculated total metabolic equivalent hours of physical activity per week, a measure of energy expenditure. There were 341 confirmed MS cases with first symptoms after baseline. Participants also reported early-life activity. To estimate relative rates (RRs) and 95% confidence intervals (CIs), we used Cox proportional hazards models, adjusting for age, latitude of residence at age 15, ethnicity, smoking, supplemental vitamin D, and body mass index at age 18. RESULTS: Compared with women in the lowest baseline physical activity quartile, women in the highest quartile had a 27% reduced rate of MS (RRpooled = 0.73, 95% CI 0.55-0.98; p-trend 0.08); this trend was not present in 6-year lagged analyses. Change in physical activity analyses suggested that women reduced activity before onset of MS symptoms. In NHS and NHS II, higher strenuous activity at ages 18-22 years was weakly associated with a decreased MS rate. However, in NHS II, total early-life activity at ages 12-22 was not associated with MS. CONCLUSIONS: Though higher physical activity at baseline was weakly associated with lower MS risk, this may have been due to women reducing physical activity in response to subclinical MS.

Epidemiology of Major Neurodegenerative Diseases in Women: Contribution of the Nurses' Health Study.

OBJECTIVES: To review the contribution of the Nurses' Health Study (NHS) to identifying the role of lifestyle, diet, and genetic or biological factors in several neurodegenerative diseases, including cognitive decline, multiple sclerosis, Parkinson's disease, and amyotrophic lateral sclerosis. METHODS: We completed a narrative review of the publications of the NHS and NHS II between 1976 and 2016. RESULTS: In primary findings for cognitive function, higher intake of nuts, moderate alcohol consumption, and higher physical activity levels were associated with better cognitive function. Flavonoids, physical activity, and postmenopausal hormone therapy were related to cognitive decline over 2 to 6 years. The NHS also has been integral in establishing Epstein-Barr virus infection, inadequate vitamin D nutrition, cigarette smoking, and obesity as risk factors for multiple sclerosis and inverse associations between cigarette smoking and caffeine and risk of Parkinson's disease. Increased risk of amyotrophic lateral sclerosis has been associated with cigarette smoking and decreased risk associated with obesity. CONCLUSIONS: The NHS has provided invaluable resources on neurodegenerative diseases and contributed to their etiological understanding. We anticipate that the NHS cohorts will continue to make important contributions to the field of neurodegenerative diseases.

Epidemiology of Multiple Sclerosis: From Risk Factors to Prevention-An Update.

Although genetic susceptibility explains the clustering of multiple sclerosis (MS) within families and the sharp decline in risk with increasing genetic distance, it cannot fully explain the geographical variations in MS frequency and the changes in risk that occur with migration, which support the action of strong environmental factors. Among these, vitamin D status, obesity in early life, infection with the Epstein-Barr virus, and cigarette smoking are the most consistent environmental predictors of MS risk. The authors review the epidemiological data, critically discuss the evidence for causality of these and other associations, and briefly review the possibility of interventions to reduce MS risk.

EBV and Autoimmunity.

Although a role of EBV in autoimmunity is biologically plausible and evidence of altered immune responses to EBV is abundant in several autoimmune diseases, inference on causality requires the determination that disease risk is higher in individuals infected with EBV than in those uninfected and that in the latter it increases following EBV infection. This determination has so far been possible only for multiple sclerosis (MS) and, to some extent, for systemic lupus erythematosus (SLE), whereas evidence is either lacking or not supportive for other autoimmune conditions. In this chapter, we present the main epidemiological findings that justify the conclusion that EBV is a component cause of MS and SLE and possible mechanisms underlying these effects.

No association of multiple sclerosis activity and progression with EBV or tobacco use in BENEFIT.

OBJECTIVE: To evaluate whether Epstein-Barr virus (EBV) immunoglobulin G (IgG) antibody levels or tobacco use were associated with conversion to multiple sclerosis (MS) or MS progression/activity in patients presenting with clinically isolated syndrome (CIS). METHODS: In this prospective, longitudinal study, we measured EBV IgG antibody and cotinine (biomarker of tobacco use) levels at up to 4 time points (baseline, months 6, 12, and 24) among 468 participants with CIS enrolled in the BENEFIT (Betaferon/Betaseron in Newly Emerging Multiple Sclerosis for Initial Treatment) clinical trial. Outcomes included time to conversion to clinically definite or McDonald MS, number of relapses, Expanded Disability Status Scale (EDSS) changes, brain and T2 lesion volume changes, and number of new active lesions over 5 years. Analyses were adjusted for age, sex, treatment allocation, baseline serum 25-hydroxyvitamin D level, number of T2 lesions, body mass index, EDSS, steroid treatment, and CIS onset type. RESULTS: We found no associations between any EBV IgG antibody or cotinine levels with conversion from CIS to MS or MS progression as measured by EDSS or activity clinically or on MRI. The relative risk of conversion from CIS to clinically definite MS was 1.14 (95% confidence interval 0.76-1.72) for the highest vs the lowest quintile of EBNA-1 IgG levels, and 0.96 (95% confidence interval 0.71-1.31) for cotinine levels >25 ng/mL vs <10. CONCLUSIONS: Neither increased levels of EBV IgG antibodies, including against EBNA-1, nor elevated cotinine levels indicative of tobacco use, were associated with an increased risk of CIS conversion to MS, or MS activity or progression over a 5-year follow-up.

The initiation and prevention of multiple sclerosis.

Although strong genetic determinants of multiple sclerosis (MS) exist, the findings of migration studies support a role for environmental factors in this disease. Through rigorous epidemiological investigation, Epstein-Barr virus infection, vitamin D nutrition and cigarette smoking have been identified as likely causal factors in MS. In this Review, the strength of this evidence is discussed, as well as the potential biological mechanisms underlying the associations between MS and environmental, lifestyle and dietary factors. Both vitamin D nutrition and cigarette smoking are modifiable; as such, increasing vitamin D levels and smoking avoidance have the potential to substantially reduce MS risk and influence disease progression. Improving our understanding of the environmental factors involved in MS will lead to new and more-effective approaches to prevent this disease.

Epstein-Barr virus neutralizing antibody levels and risk of multiple sclerosis.

Previous infection with Epstein-Barr virus (EBV) and infectious mononucleosis are established multiple sclerosis (MS) risk factors, and elevated serum titers of anti-EBV nuclear antigen (anti-EBNA) antibodies in healthy adults are strongly correlated with future MS risk. In this prospective study, we investigated the association between EBV neutralizing antibodies and MS risk. MS risk tended to be higher in individuals with high titers of neutralizing antibodies compared to those with low titers (relative risk [RR] = 2.2, 95% confidence interval [CI] 0.97-5.1). This association was attenuated after adjustment for anti-EBNA1 IgG Ab titers (RR = 1.4, 95% CI 0.5-3.5). This preliminary finding warrants further study in a larger population.

XVI European Charcot Foundation lecture: nutrition and environment: can MS be prevented?

Multiple sclerosis (MS) is a relatively common debilitating neurologic disease that affects people in early adulthood. While the characteristic pathology of MS has been well described, the etiology of the disease is not well understood, despite decades of research and the identification of strong genetic and environmental candidates for susceptibility. A question central to all diseases, but posed specifically for MS at the XVI European Charcot Foundation Lecture, was 'Can MS be prevented?' To address this question, we have evaluated the available data regarding nutritional and environmental factors that may be related to MS susceptibility and suggest the extent to which a potential intervention may reduce disease burden. It is our opinion that intervention, particularly supplementation with vitamin D, could have a dramatic impact on disease prevalence. Understanding that any intervention or behavioral modification will surely act in the context of genetic susceptibility and unidentified stochastic events, it is likely that not all MS is 'preventable'. Epidemiologic observation has provided key insights into environmental and nutritional factors that may alter one's susceptibility to MS, however, there are still many questions in unraveling the etiology of this complex disease.