Multiple sclerosis (MS) is a chronic, autoimmune inflammatory disease of the central nervous system (CNS) with increasing prevalence. It is a progressive condition, which often worsens over time.

MS is the most common debilitating neurodegenerative disease among young adults. Symptoms typically appear between the ages of 20 and 40, but they can manifest at any age.

Experts believe that genetic and environmental factors, such as smoking, obesity, and exposure to ultraviolet B (UVB) light, may increase the likelihood of MS onset.

Researchers at the Università del Piemonte Orientale in Novaro, Italy, analyzed the extensive UK Biobank to investigate links between diet, lifestyle factors, and MS. Their findings were published in the journal Nutrients.

The Connection Between MS and Gut Health

MS is a neurodegenerative disease that causes the immune system to attack myelin, a substance that coats nerve fibers. This results in lesions in the CNS, which can lead to physical or cognitive impairments, including sensory disturbances, visual impairments, lack of coordination, and paralysis. MS subtypes include clinically isolated syndrome, primary progressive MS, relapsing-remitting MS, and secondary progressive MS. Women with MS outnumber men two to one.

Researchers have long been studying MS to identify interventions that could reduce the risk of developing the disease. Diet has been a significant focus of this research, particularly concerning its impact on gut health and, consequently, CNS health.

The researchers noted that a pro-inflammatory gut environment might elevate neuroinflammation and increase MS risk. They emphasized the importance of considering diet as a crucial modulator of gut homeostasis and CNS health.

Dietary Data from the UK Biobank

The study's authors used data from the UK Biobank, one of the largest biomedical databases available, to address the lack of large-scale prospective studies on dietary exposures in the general population. The initial study cohort included 502,507 UK residents aged 40-69. MS presence was determined by hospital admissions with MS diagnoses or self-reported MS diagnoses.

In 2006, participants completed a food frequency questionnaire (FFQ), reporting their usual consumption of 29 different food groups and alcohol over the previous year. They answered questions about their daily intake of cooked vegetables, raw vegetables, fresh and dried fruits, and their weekly intake of fatty fish, processed meats, beef, lamb, poultry, cheese, added salt, and other foods. A subsample also completed online interviews recalling their dietary choices over the previous 24 hours.

The dietary data allowed researchers to evaluate the impact of single micro- or macronutrient intake on disease risk and calculate participants’ Mediterranean Diet scores. After excluding participants due to retractions or missing information, the final cohort included 499,563 people.

Fatty Fish Consumption and MS Risk

During an average of 12 years of follow-up, 478 MS cases were identified, indicating a prevalence rate of 7.78 MS cases per 100,000 person-years. Increased MS risk was observed among individuals who smoked, had a vitamin D deficiency, or had a history of Epstein-Barr virus infection. Genetic determinants for obesity, including childhood obesity, were also linked to higher MS risk.

The study found an inverse correlation between adherence to a Mediterranean diet and MS onset, suggesting that a healthy, plant- and whole-food-rich diet, including moderate fatty fish consumption, may protect against MS. Interestingly, consuming fatty fish once a week appeared to be more protective than more frequent consumption.

Study Implications and Limitations

The study's findings were discussed with registered dietitians Kelsey Costa, MS, RDN, and Sarah Hormachea, MS, RD, BC-ADM, CDCES. Costa highlighted the strength of using the comprehensive UK Biobank database. However, both dietitians expressed concerns about the study's limitations.

Hormachea noted that the UK Biobank cohort consists mainly of white, high-income individuals, which may not represent the general population. She cautioned that participants who volunteer for such studies often have different health behaviors and socio-economic statuses compared to those who do not participate. Costa pointed out the underrepresentation of ethnic minority groups, which might limit the findings' applicability to those populations.

Recall bias was another concern, as participants might not accurately remember or report their food intake. Costa also mentioned that the small number of MS cases could reduce the statistical power of the analysis, making it difficult to observe small effects accurately. Potential confounding factors, such as nutrient density and cooking methods, were not assessed.

Lastly, due to the study's observational nature, causality cannot be established. Hormachea suggested that reverse causality might be an issue, as people diagnosed with MS could have changed their eating habits subsequently.