Caesarean section and infant formula feeding are associated with an earlier age of onset of multiple sclerosis

•We studied the influence of mode of delivery and lactation on age at MS onset (AAO).•208/2055 patients (11%) were born from C-section, 563/2055 (27%) had infant formula.•C-section was associated with an earlier AAO (−5.2 yrs) than vaginal delivery.•Infant formula was associated with an earlier AAO (−4.2 yrs) than breastfeeding.•These associations were more apparent in patients without a family history of MS.