Effect of occupation on risk of developing MS: an insurance cohort study

Allopurinol use and risk of multiple sclerosis

BACKGROUND

Low uric acid levels have been observed in patients with multiple sclerosis (MS). As allopurinol is commonly used to lower uric acid in gout patients, this study examined allopurinol use in individuals with MS during the five years before diagnosis, compared to a matched control group.

METHODS

This nationwide case-control study used Danish health registry data. 9,063 individuals diagnosed with MS between 2008 and 2023 were included on the day of MS diagnosis, while 90,630 controls, were matched from the general population. Controls were matched on age, gender, place of residence, and inclusion date. Allopurinol prescriptions were tracked annually for five years prior to the inclusion date. The primary outcome was the odds ratio of allopurinol use in MS patients compared to controls, analyzed using conditional logistic regression.

RESULTS

In the five years prior to the MS diagnosis or matching date for controls, allopurinol use was consistently lower in MS cases. In total, 0.30% (n = 27) of MS cases had at least one allopurinol prescription, compared to 0.62% (n = 558) of controls, corresponding to an odds ratio of 0.48 (95% CI: 0.33-0.71).

CONCLUSIONS

Individuals diagnosed with MS had significantly lower allopurinol use in the five years preceding their diagnosis, suggesting an inverse relationship between uric acid levels and MS risk. Reduced uric acid levels may be associated with early MS development, possibly due to its antioxidant properties or metabolic changes. Alternatively, these findings suggest a possible protective effect of allopurinol against MS, warranting further investigation.

Leveraging Administrative Health Databases to Address Health Challenges in Farming Populations: Scoping Review and Bibliometric Analysis (1975-2024)

BACKGROUND

Although agricultural health has gained importance, to date, much of the existing research relies on traditional epidemiological approaches that often face limitations related to sample size, geographic scope, temporal coverage, and the range of health events examined. To address these challenges, a complementary approach involves leveraging and reusing data beyond its original purpose. Administrative health databases (AHDs) are increasingly reused in population-based research and digital public health, especially for populations such as farmers, who face distinct environmental risks.

OBJECTIVE

We aimed to explore the reuse of AHDs in addressing health issues within farming populations by summarizing the current landscape of AHD-based research and identifying key areas of interest, research gaps, and unmet needs.

METHODS

We conducted a scoping review and bibliometric analysis using PubMed and Web of Science. Building upon previous reviews of AHD-based public health research, we conducted a comprehensive literature search using 72 terms related to the farming population and AHDs. To identify research hot spots, directions, and gaps, we used keyword frequency, co-occurrence, and thematic mapping. We also explored the bibliometric profile of the farming exposome by mapping keyword co-occurrences between environmental factors and health outcomes.

RESULTS

Between 1975 and April 2024, 296 publications across 118 journals, predominantly from high-income countries, were identified. Nearly one-third of these publications were associated with well-established cohorts, such as Agriculture and Cancer and Agricultural Health Study. The most frequently used AHDs included disease registers (158/296, 53.4%), electronic health records (124/296, 41.9%), insurance claims (106/296, 35.8%), population registers (95/296, 32.1%), and hospital discharge databases (41/296, 13.9%). Fifty (16.9%) of 296 studies involved >1 million participants. Although a broad range of exposure proxies were used, most studies (254/296, 85.8%) relied on broad proxies, which failed to capture the specifics of farming tasks. Research on the farming exposome remains underexplored, with a predominant focus on the specific external exposome, particularly pesticide exposure. A limited range of health events have been examined, primarily cancer, mortality, and injuries.

CONCLUSIONS

The increasing use of AHDs holds major potential to advance public health research within farming populations. However, substantial research gaps persist, particularly in low-income regions and among underrepresented farming subgroups, such as women, children, and contingent workers. Emerging issues, including exposure to per- and polyfluoroalkyl substances, biological agents, microbiome, microplastics, and climate change, warrant further research. Major gaps also persist in understanding various health conditions, including cardiovascular, reproductive, ocular, sleep-related, age-related, and autoimmune diseases. Addressing these overlooked areas is essential for comprehending the health risks faced by farming communities and guiding public health policies. Within this context, promoting AHD-based research, in conjunction with other digital data sources (eg, mobile health, social health data, and wearables) and artificial intelligence approaches, represents a promising avenue for future exploration.

Low Sun Exposure Is Associated with Both Progressive-Onset and Relapse-Onset Multiple Sclerosis Risk: A Case-Control Study

BACKGROUND

Sun exposure has consistently been associated with multiple sclerosis (MS) onset, but case samples are predominantly relapse-onset MS (ROMS), and risk estimates have rarely been reported separately for ROMS and progressive-onset MS (POMS). We aimed to determine whether sun exposure prior to disease onset was associated with POMS and whether the effect differed between POMS and ROMS.

METHODS

This nationwide case-control study included 153 POMS cases, 204 incident ROMS cases, and 558 community controls with data from two separate datasets: the PPMS Study (2015-2021) and the Ausimmune Study (2003-2006). Information on time spent in the sun before the first MS symptom, skin phenotype, and sun protection behavior was collected. Satellite data on ambient ultraviolet radiation (UVR) were used to calculate cumulative UVR dose. Unconditional logistic regression was used with adjustment for covariates.

RESULTS

There were consistent dose-response associations, with higher levels of UVR exposure associated with a reduced risk of POMS, both for leisure-time and occupational UVR from age 6 to symptom onset. Associations were overall stronger for POMS than ROMS. For example, cumulative leisure-time UVR dose (per 100 kJ/m2 increment) was associated with POMS (aOR 0.93, 95% CI: 0.91-0.95) and the association was slightly weaker for ROMS (aOR 0.96, 95% CI: 0.94-0.99) for age 6 to symptom onset (test for interaction p < 0.001).

CONCLUSIONS

Low levels of sun exposure, throughout the whole lifespan, are associated with an increased risk of POMS and ROMS onset. The sun effects are usually stronger for POMS than ROMS.

Causal effects of dietary composition on multiple sclerosis risk and severity: a Mendelian randomization study

Objectives

Observational studies have found potential associations between dietary intake and multiple sclerosis (MS). However, these associations are inconsistent, and the causal relationship remains unclear. In this study, we aim to examine the causal relationship between genetically predicted dietary composition and the risk and severity of MS using two-sample Mendelian randomization.

Method

Genetic instruments for 30 different dietary compositions were extracted from large-scale genome-wide association studies (GWAS), mainly from the UK Biobank dataset. The GWAS data for MS risk and severity were obtained from the International Multiple Sclerosis Genetics Consortium. The primary analysis employed either the inverse variance weighted method or the Wald ratio method to evaluate the causal association. Several sensitivity analyses were also performed.

Results

Genetically predicted higher pork intake was causally associated with an increased risk of MS (odds ratio [OR] = 6.76; p = 0.005), while genetically driven higher cereal intake (OR = 0.43, p = 0.016), vitamin C supplement (OR < 0.01; p = 4.34 × 10-5), folic acid supplement (OR < 0.01; p = 4.91 × 10-71), and fish oil supplement (OR = 0.04; p = 0.017) were causally linked to a decreased risk of MS. In addition, genetically predicted higher alcoholic intake (OR = 1.17; p = 0.041) was causally associated with an increase in MS severity, while folic acid supplement (OR < 0.01; p = 0.015) was causally linked to a decrease in MS severity.

Interpretation

This study found that increased consumption of cereal, vitamin C, folic acid, and fish oil, coupled with reduced pork and alcohol intake, may potentially decrease the risk and severity of MS. These findings inform the development of dietary-based strategies for MS prevention and treatment.

Milk and multiple sclerosis: A possible link?

Despite having been formally defined over 150 years ago, the etiology of multiple sclerosis (MS) is still relatively unknown. However, it is now recognized as a multifactorial disease in which genetics, infection, immune function, and environment play a role. We propose an additional piece to the puzzle: milk. In this review, milk is highlighted as a potential risk factor for MS. We examine the overall correlation between bovine milk consumption and the incidence of MS. We then discuss possible mechanisms that may explain the positive association between milk consumption and the development of MS. For instance, butyrophilin (BTN), a milk glycoprotein, can provide molecular mimicry of myelin oligodendrocyte glycoprotein and induce an autoinflammatory response against myelin. Other milk components such as casein, gangliosides, xanthine oxidase, and saturated fats are also analyzed for their potential involvement in the pathophysiology of MS. Finally, we fit milk alongside other well known risk factors of MS: vitamin D levels, Epstein Barr virus infection, and gut dysbiosis. In conclusion, this review summarizes potential mechanisms linking milk as an underappreciated potential risk factor for the development of MS.

The risk of multiple sclerosis on the Orkney islands. A review of the search for distinctively Orcadian risks, with a hypothesis for further investigations

The most extensive and meticulous epidemiological study yet to be published on the frequency of multiple sclerosis (MS) across the regions of Scotland has confirmed that the high incidence of MS on the Orcadian islands is unique and is most probably the highest in the world. Environmental and genetic studies of Orcadian MS have been carried out over many years but the results have been discouragingly inconclusive; no convincing explanation of the distinctively high Orcadian MS risks has come to light. However, studies of both prevalence and incidence of MS over a time line of approximately five decades, show that Orcadian MS has steadily increased to significantly exceed the neighbouring genetically related populations including North Eastern Scotland and the Shetland islands. Over this period the islands have progressively expanded occupations related to agriculture and have simultaneously acquired the highest concentration of cattle in Europe. Coinciding high and increasing Orcadian MS risk with increasing agricultural activities including bovine density and dairying, points towards a potential but unexpected causal risk. Raised incidence of MS with farming and in particular with dairy farming have been documented in Australia, Denmark, and more recently in Norway, further pointing to a possible MS risk associated with agricultural activities. A clue to the cause of this curious association has unexpectedly emerged from laboratory studies. Using very rarely available tissues from patients coming to autopsy during an MS attack, a toxin known as beta-haemolysin (sphingomyelinase), which is produced by the bacterium Staphylococcus aureus, has been identified in the affected tissues. Staph aureus is a common inhabitant of the mucosal linings of the human nasal sinuses and sinus mucosal inflammations have been shown to be closely associated with attacks of MS and optic neuritis. Irrespective of origin, human or animal, all strains of Staph aureus carry the beta haemolysin gene. However, the toxin is only sporadically expressed by the strains most commonly isolated from human carriers. Strains carried by bovines nearly always express toxin. Has the increasing high risk of MS in Orcadians been promoted by the nasal transmission and subsequent establishment of the high secreting bovine genotypes of Staph aureus in the Orcadian population? To demonstrate that bovine associated strains of Staph aureus are carried more frequently in the Orcadian population (or even specifically in Orcadian MS cases), would not of itself necessarily explain the high prevalence of Orcadian MS. It would however clearly justify an in-depth exploration of the nasal bacterial microbiome of MS cases. This should include the incidence of beta-toxin secreting Staph aureus genotypes. If MS cases are shown to have a distinctive nasal bacterial microbiome, including beta-toxin secretors, this finding would open up an almost entirely new range of investigations and approaches to the understanding of the pathogenesis of MS.

Occupational risk factors for multiple sclerosis: a systematic review with meta-analysis

Objective

We decided to conduct the first systematic review with meta-analysis to provide the highest level of up-to-date evidence on the occupational risk factors for Multiple Sclerosis.

Methods

A systematic, comprehensive literature search was performed in four electronic academic databases. We included any case-control study that enrolled working-age subjects and compared the proportion of MS cases with controls who were not exposed to an occupational risk factor. The primary outcome was the occurrence of MS. The quality assessment was performed with the Critical Appraisal Checklist for Case Control Studies, developed, and validated by the Joanna Briggs Institute. All the selection process was also carried out by two independent and previously trained researchers.

Results

Overall, the total sample included 19,004 people with MS and 4,164,162 controls. Agricultural workers (OR = 1.44, 95% CI 1.13-1.83), offshore workers (OR = 3.56, 95% CI 2.74-4.61), and hairdressers (OR = 8.25, 95% CI 1.02-66.52) were associated with a higher probability of being diagnosed with MS. In parallel, workers exposed to toxic fumes from oil wells (OR = 16.80, 95% CI 8.33-33.90), low-frequency magnetic fields (OR = 1.71, 95% CI 1.03-2.72), and pesticides (OR = 3.17, 95% CI = 2.53-3.99) also had an increased likelihood of having MS.

Conclusion

Our study has the potential to influence more assertive public policies. Nevertheless, future studies on how the occupational setting may contribute to the incidence of MS are highly recommended.

Systematic review registration

The protocol was registered in the international prospective register of systematic reviews (PROSPERO- CRD42023443257).

Nasal Microbiota and Neuroinflammation: Relationship between Nasal Flora and Multiple Sclerosis Onset/Progression

The role of nasal microbiota in contributing to neuroinflammation is gradually emerging. Multiple sclerosis and chronic rhinosinusitis share important clinical and epidemiological similarities, and the hypothetical connection among these two pathological entities should be carefully investigated. This editorial is based on a review of available literature on this topic. The main international databases were searched using the following keywords: neuroinflammation, nasal microbiota, multiple sclerosis, chronic rhino-sinusal disorders, chronic sinusitis. Four fully-consistent articles that investigated nasal microbiota alteration and/or chronic rhinosinusitis presence in subjects affected by multiple sclerosis were identified. Overall, these studies showed a significant connection between nasal microbiota dysbiosis and the presence of multiple sclerosis. New specific studies to analyze the nasal microbiota and its metabolism in patients affected by multiple sclerosis should be performed. In fact, a series of treatments able to change this flora could improve the rhino-sinusal state with consequent reduction of recurrent episodes of neuro-inflammation.

Medicinal herbs and multiple sclerosis: Overview on the hard balance between new therapeutic strategy and occupational health risk

Multiple sclerosis (MS) is an autoimmune disease characterized by demyelination and axonal loss of the central nervous system (CNS). Despite its spread throughout the world, the mechanisms that determine its onset are still to be defined. Immunological, genetic, viral, and environmental factors and exposure to chemicals may trigger MS. Many studies have highlighted the anti-inflammatory and anti-oxidant effects of medicinal herbs, which make them a natural and complementary treatment for neurodegenerative diseases. A severe reduction of several MS symptoms occurs with herbal therapy. Thus, the request for medicinal plants with potential beneficial effects, for MS patients, is constantly increasing. Consequently, a production increase needs. Unfortunately, many medicinal herbs were untested and their action mechanism, possible adverse effects, contraindications, or interactions with other drugs, are poorly or not investigated. Keeping in mind the pathological mechanisms of MS and the oxidative damages and mitochondrial dysfunctions induced by pesticides, it is important to understand if pesticides used to increase agricultural productivity and their residues in medicinal plants, may increase the risk of developing MS in both workers and consumers. Studies providing some indication about the relationship between environmental exposure to pesticides and MS disease incidence are few, fragmentary, and discordant. The aim of this article is to provide a glance at the therapeutic potential of medicinal plants and at the risk for MS onset of pesticides used by medicinal plant growers and present in medicinal herbs.

Bacterial transportable toxins of the nasopharyngeal microbiota in multiple sclerosis. Nose-to-brain direct

Intranasal administration delivers molecules directly to the brain bypassing the blood-brain barrier. Three distinct routes of access have been identified; olfactory, trigeminal and via the paranasal sub-mucosa of the posterior sinuses. Consequently, environmental toxins may access the CNS directly to induce inflammatory and degenerative disease. They may also activate bacterial species of the nasal mucosal microbiome to release both immune-deviating cell wall antigens and transportable neurotoxins with local direct access to the CNS. Evidence is reviewed that toxins of the nasal bacterial microbiota may be directly implicated in the inflammatory and degenerative pathogenesis of multiple sclerosis.

Mortalità per patologie neurologiche e prodotti fitosanitari: ipotesi eziologiche da un’analisi spaziale della provincia di Pavia

BACKGROUND

Neurological and neurodegenerative diseases are multifactorial and their causes are not well understood yet. Among the relevant risk factors, pesticides and the productive activities in which they are used are included.

OBJECTIVES

To evaluate the association of mortality from neurological diseases within the Province of Pavia (Italy) with the agricultural activities, as a proxy of pesticides exposure.

METHODS

Population data for 2012 were provided by the local health unit (ATS) and by the registry office of the Regional Health Service. Spatial analyses were carried out by both a classical and Bayesian approach, to obtain a mortality map of the relative risk for neurological diseases in the Province of Pavia. Spatial distribution of main agricultural activities within the same territory, used as proxy of pesticides use, was made possible by data from the Geoportale Territoriale of the Lombardy region. Finally, a comparison between spatial distribution of mortality from neurological diseases and spatial distribution of main agricultural activities has been conducted.

RESULTS

Mortality for neurological diseases in the Province of Pavia in 2012 was 4.41 for men and 6.53 for women per 10,000 subjects living in this area. Female mortality for neurological diseases showed a cluster in the Oltrepò district, where viticulture and fruit/horticulture are more common than elsewhere. More precisely, Bayesian relative risk (RR) had higher values in comparison with the median RR of the Province (100.8), with a posterior probability (PP) between 0.75 and 0.95 (not significant). Similarly, mortality for Parkinson's disease in women showed RR greater than the median value of the Province (100.6), with PP between 0.25 and 0.75 (not significant).

CONCLUSIONS

Notwithstanding the ecological nature of the study, our results suggest the need to further investigate the possible link between pesticides exposure or related activities and neurological and neurodegenerative diseases, particularly Parkinson's disease. An ad hoc study on a random sample of the population living in the Province of Pavia, with the collection of individual data by means of standardized questionnaire, would allow to control for biases usually present when an ecological study design is applied.

Mortalità per patologie neurologiche e prodotti fitosanitari: ipotesi eziologiche da un’analisi spaziale della provincia di Pavia

BACKGROUND

Neurological and neurodegenerative diseases are multifactorial and their causes are not well understood yet. Among the relevant risk factors, pesticides and the productive activities in which they are used are included.

OBJECTIVES

To evaluate the association of mortality from neurological diseases within the Province of Pavia (Italy) with the agricultural activities, as a proxy of pesticides exposure.

METHODS

Population data for 2012 were provided by the local health unit (ATS) and by the registry office of the Regional Health Service. Spatial analyses were carried out by both a classical and Bayesian approach, to obtain a mortality map of the relative risk for neurological diseases in the Province of Pavia. Spatial distribution of main agricultural activities within the same territory, used as proxy of pesticides use, was made possible by data from the Geoportale Territoriale of the Lombardy region. Finally, a comparison between spatial distribution of mortality from neurological diseases and spatial distribution of main agricultural activities has been conducted.

RESULTS

Mortality for neurological diseases in the Province of Pavia in 2012 was 4.41 for men and 6.53 for women per 10,000 subjects living in this area. Female mortality for neurological diseases showed a cluster in the Oltrepò district, where viticulture and fruit/horticulture are more common than elsewhere. More precisely, Bayesian relative risk (RR) had higher values in comparison with the median RR of the Province (100.8), with a posterior probability (PP) between 0.75 and 0.95 (not significant). Similarly, mortality for Parkinson's disease in women showed RR greater than the median value of the Province (100.6), with PP between 0.25 and 0.75 (not significant).

CONCLUSIONS

Notwithstanding the ecological nature of the study, our results suggest the need to further investigate the possible link between pesticides exposure or related activities and neurological and neurodegenerative diseases, particularly Parkinson's disease. An ad hoc study on a random sample of the population living in the Province of Pavia, with the collection of individual data by means of standardized questionnaire, would allow to control for biases usually present when an ecological study design is applied.

The Autoimmune Ecology

Autoimmune diseases (ADs) represent a heterogeneous group of disorders that affect specific target organs or multiple organ systems. These conditions share common immunopathogenic mechanisms (i.e., the autoimmune tautology), which explain the clinical similarities they have among them as well as their familial clustering (i.e., coaggregation). As part of the autoimmune tautology, the influence of environmental exposure on the risk of developing ADs is paramount (i.e., the autoimmune ecology). In fact, environment, more than genetics, shapes immune system. Autoimmune ecology is akin to exposome, that is all the exposures - internal and external - across the lifespan, interacting with hereditary factors (both genetics and epigenetics) to favor or protect against autoimmunity and its outcomes. Herein, we provide an overview of the autoimmune ecology, focusing on the immune response to environmental agents in general, and microbiota, cigarette smoking, alcohol and coffee consumption, socioeconomic status (SES), gender and sex hormones, vitamin D, organic solvents, and vaccines in particular. Inclusion of the autoimmune ecology in disease etiology and health will improve the way personalized medicine is currently conceived and applied.

Role of socio-economic and reproductive factors in the risk of multiple sclerosis

The incidence of multiple sclerosis is increasing in Danish women. Their risk of developing multiple sclerosis has more than doubled in 25 years while it has remained virtually unchanged for men. The explanation for these epidemiological changes should be sought in the environment as they are too rapid to be explained by gene alterations. We investigated the effect of numerous biological social physical and chemical environmental exposures in different periods of life. These data were available from population-based registries and were used in a case-control approach. This study database included all multiple sclerosis cases (n = 1403) from the Danish MS Registry with clinical onset between 2000 and 2004 as well as 35,045 controls drawn by random from the Danish Civil Registration System and matched by sex year of birth and residential municipality at the reference year. Having newborn children reduced the risk of multiple sclerosis (MS) in women but not in men. Childbirths reduced the risk of MS by about 46% during the following 5 years. Even pregnancies terminated early had a protective effect on the risk of developing MS suggesting a temporary immunosuppression during pregnancy. Our data on social behaviour regarding educational level income and relationship stability did not indicate reverse causality. A greater likelihood to be exposed to common infections did not show any effect on the risk of MS neither in puberty nor in adulthood. Socio-economic status and lifestyle expressed in educational level and sanitary conditions in youth were not associated with the risk of MS.

Socio-economic factors and immigrant population studies of multiple sclerosis

The uneven geographical distribution of multiple sclerosis (MS) and the differences in disease severity observed between different ethnic groups indicate a complex interplay between genetic and environmental risk factors involved in the disease pathogenesis. Changes in MS risk after migration suggest influence of environmental factors on disease susceptibility. Whether the risk of MS is affected by socio-economic status (SES) is still controversial. In the present review, the combined knowledge from studies of migration and SES in MS is discussed.

Physical and social environment and the risk of multiple sclerosis

BACKGROUND

The incidence of multiple sclerosis (MS) in Denmark has doubled in women since 1970, whereas it has been almost unchanged in men. The rapid epidemiological changes suggest that environmental factors may modify the risk of MS.

OBJECTIVES

To investigate whether occupational, physical, or social environmental influence the risk of MS differently in women than in men.

METHODS

The cohort consists of all 1403 patients (939 women, 464 men) identified through Danish Multiple Sclerosis Registry aged 1-55 of years at clinical onset between 2000 and 2004, and up to 25 control persons for each case, matched by sex, year of birth and residential municipality. The same cohort was previously used to investigate the influence of the reproductive factors on the risk of MS.

RESULTS

By linkage to Danish population registers we found a slight albeit statistically significant excess for 6 female MS patients who had been employed in agriculture: OR 3.52; 95% CI 1.38-9.00, p=0.008 (0.046 when corrected for multiple significance) and a trend for exposure to outdoor work in 12 : OR 1.94, 95% CI 1.06-3.55, p=0.03 (0.09 when corrected for multiple significance), but the numbers of cases were small, and the effects were not found in men. Educational level, housing conditions in youth, or the presence of children unrelated by blood in the household did not influence the risk of MS.

CONCLUSIONS

Our study did not reveal any additional factors beyond the previously published childbirths which could explain the extent of the MS incidence increase in women.