Reduced duration of breastfeeding is associated with a higher risk of multiple sclerosis in both Italian and Norwegian adult males: the EnvIMS study.

Breastfeeding for at least 4 months has been found to be associated with a reduced risk of immune-mediated diseases including multiple sclerosis (MS). Using data from a large multinational case–control study (EnvIMS), the association between MS and breastfeeding was investigated in two distinct populations. A questionnaire (EnvIMS-Q) which included a section on feeding during the first year of life was administered to MS cases and to age and sex frequency-matched controls from Italy and Norway. Logistic regression was used to estimate the odds ratio (ORs) and 95 % confidence intervals (95 % CIs) as a measure of the association between MS and exposure to prolonged breastfeeding (4 months or more, used as the reference category), vs. no breastfeeding or breastfeeding for less than 4 months (reduced exposure). Education, smoking habits, smoking in mother’s pregnancy, and other types of milk used in infant feeding were included as covariates. A total of 547 cases and 1039 controls in Italy, and 737 cases and 1335 controls in Norway were studied. The distribution of prolonged (reference) breastfeeding differed between the Norwegian (65.4 %) and the Italian (48.9 %) study participants. A significant association between MS and reduced/no exposure to breastfeeding was found overall for Italy (ORadj = 1.37; 95 % CI 1.09, 1.73), but not for Norway (ORadj = 1.14; 95 % CI 0.92, 1.40). However, only in men, significant associations were observed for both populations (ORItaly = 2.33; 95 % CI 1.50, 3.65, ORNorway = 2.13; 95 % CI 1.37, 3.30). Reduced exposure to breastfeeding in males was found to be associated with increased risk of MS in Italy and in Norway.