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

Mode of delivery and lactation are among the earliest factors influencing gut microbiota composition and potentially MS risk, but their contribution to MS susceptibility has been controversial. We investigated whether these factors could influence age at MS onset (AAO) on 2055 RRMS patients (mean age 28.4 years). Patients born by means of a caesarean section (10.9%) had an earlier AAO than those born through natural delivery (- 5.2 years, p < 0.001). Patients fed with infant formula had an earlier AAO compared to patients breastfed, particularly considering those breastfed for at least 6 months (- 4.2 years, p < 0.001). The association of vaginal delivery and natural breastfeeding with a later AAO of MS was particularly apparent in patients without a family history of MS, while disappeared in patients with familiarity for MS. The results suggest these modifiable environmental factors which act at the population level may have an influence on the onset of the disease.