Season of birth is associated with multiple sclerosis and disease severity.

BACKGROUND: The latitude gradient in multiple sclerosis incidence indicates that low sun exposure and therefore vitamin D deficiency is associated with multiple sclerosis risk. OBJECTIVE: Investigation of the effect of month of birth, which influences postnatal vitamin D levels, on multiple sclerosis risk and severity in Sweden. METHODS: Patients and population-based controls were included from three nationwide cohorts. Differences in month of birth between cases and controls were analyzed using logistic regression and examined for effect modification by calendar year and geographic region at birth. RESULTS: Males had a reduced risk of multiple sclerosis if born in the winter and increased risk if born in the early fall. Individuals born before 1960 had an increased risk if born in summer or fall. Being born in late summer and early fall was associated with more severe disease. CONCLUSIONS: We identified a birth cohort effect on the association between the month of birth and multiple sclerosis, with a more significant effects for births before 1960. This coincides with a period of lower breastfeeding rates, recommended intake of vitamin D, and sun exposure, resulting in a lower vitamin D exposure during the fall/winter season for infants born in the summer.

Smoking and worsening disability in multiple sclerosis: A meta-analysis.

OBJECTIVES: Multiple sclerosis (MS) is a chronic demyelinating disorder affecting young adults. Environmental factors and lifestyle behaviors are pivotal in MS pathophysiology. Smoking has been considered as an important risk factor in MS. Various recent studies have been conducted to measure the role of smoking on worsening disability in patients with MS, thus we intended to systematically assess effect of smoking on evolution of disability in this study. MATERIALS & METHODS: We queried MEDLINE, EMBASE and Cochrane Library with following keywords "Multiple Sclerosis, Smoking, Tobacco Use, Disability" on December 1st 2016. Original articles were included when smoking history was mentioned, disability was measured via expanded disability status scale (EDSS) or multiple sclerosis severity score (MSSS). Studies with insufficient outcome data, non-human, or in other languages than English were excluded. RESULTS: Through literature review after duplicate removals, 268 articles were retrieved. A total of 56 articles were screened and 15 articles were assessed for eligibility, finally, eleven articles were included in this systematic review and meta-analysis. Ever smoking was significantly associated with increased EDSS (standardized mean difference (SMD) = 0.15, 95% CI = 0.01-0.28), but had no significant association with risk of reaching EDSS 4 (HR = 1.24, 95% CI = 0.89-1.72) or EDSS 6 (HR = 1.17, 95% CI = 0.88-1.57). Smoking had no effect on MSSS (SMD = 0.14, 95% CI = -0.04-0.32) or T2 lesion volume (SMD = 0.07, 95% CI = -0.08-0.22). CONCLUSIONS: This meta-analysis showed smoking increased EDSS, insignificant findings were possibly due to the small number of studies, significant differences in methodologies, and variations in reporting of disability outcomes.