Breastfeeding, ovulatory years, and risk of multiple sclerosis

Abstract

Objective: To determine whether women who breastfeed their infants longer or have fewer ovulatory years are at lower risk of developing multiple sclerosis (MS).

Methods: We recruited women with newly diagnosed MS or its precursor, clinically isolated syndrome (CIS) (n = 397), and matched controls (n = 433) into the MS Sunshine Study from the membership of Kaiser Permanente Southern California. A structured in-person questionnaire was administered to collect the behavioral (pregnancies, breastfeeding, hormonal contraceptive use) and biological (age at menarche and menopause, amenorrhea) factors to make up ovulatory years.

Results: Among women who had live births, a cumulative duration of breastfeeding for ≥15 months was associated with a reduced risk of MS/CIS (adjusted odds ratio [OR] 0.47, 95% confidence interval [CI] 0.28-0.77; p = 0.003 compared to 0-4 months of breastfeeding). Being ≥15 years of age at menarche was also associated with a lower risk of MS/CIS (adjusted OR 0.56, 95% CI 0.33-0.96; p = 0.035). Total ovulatory years and the remaining factors that determine it, including gravidity, parity, episodes of amenorrhea, and hormonal contraceptive use, as well as age at first birth, showed no significant association with the risk of MS/CIS.

Conclusions: Mothers who breastfeed longer may be at lower subsequent risk of developing multiple sclerosis. This is consistent with the other known maternal health benefits of breastfeeding and with our previous observation that women with MS who breastfeed exclusively are at lower risk of postpartum relapses.

Figure. Duration of breastfeeding and MS

Depicted are the crude (top) and adjusted (bottom) odds ratios (ORs) and 95% confidence intervals (95% CIs) of the association between the cumulative duration of breastfeeding among women with live births before symptom onset (cases) or index date (controls) and multiple sclerosis (MS)/clinically isolated syndrome (CIS). The numbers of cases and matched controls in each analysis are listed in the right column. The cumulative duration of breastfeeding is represented in tertiles based on the distribution among the controls. ORs are adjusted for age, smoking, race/ethnicity, and parity. Cumulative duration of breastfeeding for >15 months was associated with a significantly lower risk of MS/CIS in both crude and adjusted analyses (p = 0.001 and 0.003 for trend, respectively).