Environmental risk factors of late-onset multiple sclerosis: A population-based case-control study

Late-onset multiple sclerosis (LOMS) was increasingly reported over the past two decades. Understanding the risk factors associated with LOMS can help improve early diagnosis, prevention strategies, and patients' quality of life. This study aimed to assess various environmental risk factors in the patients with late-onset disease.

This study utilized a population-based case-control study design. Primary data on verified LOMS cases were received from Iran's national MS registry, with additional information gained via telephone interviews. The potential risk factors for LOMS were examined using a questionnaire modified from global case-control studies. Age and sex-matched healthy controls were selected using face-to-face interviews. The collected data were analyzed using matched logistic regression in Stata software version 14, reporting adjusted odds ratios (OR), and 95 % confidence intervals, with a significance level set at p < 0.05.

This study examined 82 LOMS cases and 207 matched controls. The mean age of cases and controls was 61 years. The findings revealed that moderate and high sunlight exposure during adolescence were related with 0.33 (95 % CI: 0.18-0.58) and 0.15 (95 % CI: 0.04-0.46) times decreased risks of developing LOMS, respectively. Similarly, compared to those with low sunlight exposure, participants with high and moderate sunlight exposure during adulthood had a lower chance of developing MS disease (OR = 0.35, 95 % CI: 0.18-0.69) and (OR = 0.40 95 % CI: 0.18-0.85) receptively. Moreover, age at first menstruation (p = 0.45), age at first delivery (p = 0.49), abortion history (p = 0.79), and oral contraceptive consumption (p = 0.18) did not significantly differ among the groups (all p > 0.05). The odds of developing LOMS were 2.47 (95 % CI: 1.05-5.81) times higher for 10 to 90 min of heavy physical activity per week and 2.39 (95 % CI: 1.08-5.27) times higher for over 90 min. Various emotional stress, including death of a loved one (OR = 2.19, 95 % CI: 1.07-4.48), family disruption (OR = 2.93 95 % CI: 1.62-1.02), homelessness (OR = 9.1 95 % CI: 1.4-57.5), employment dismissal (OR = 4.0, 95 % CI: 1.31-12.1), and unemployment (OR = 3.1, 95 % CI: 1.25-7.62), were significantly associated with an increased risk of developing LOMS. Depression (OR = 5.5, 95 % CI: 2.7-10.9), measles (OR = 2.63, 95 % CI: 1.4-4.8), and a family history of MS (OR = 4.7, 95 % CI: 1.4-15.6) were also associated with higher risk of LOMS development.

Sunlight exposure was shown to have a strong protective impact against LOMS. Furthermore, intensive physical activity, psychological stresses such as family upheavals, medical illnesses such as depression, and a positive family history of MS may all be associated with an increased risk of LOMS. These findings emphasized the importance of preventive measures for older individuals affected by the disease.