In Norway, as in all Nordic countries, breastfeeding is strongly recommended and supported. We believe that breastfeeding is beneficial both for the mother and child. The recommendation from the national health authorities is exclusive breastfeeding for six months.

In the mid-1990s, an international team led by Prof Michael Kramer from Canada conducted the PROBIT trial, a large randomised controlled study (RCT) of a breastfeeding intervention campaign in Belarus, in which more than 17,000 mothers and children participated. Half of the maternity hospitals and their affiliated clinics were randomised to receive the intervention (modelled on the WHO/UNICEF Baby-Friendly Hospital Initiative), while the others continued as before. Interestingly, the investigators found that in those who received intervention succeeded in increasing both the exclusivity and duration of breastfeeding but did not result in lowering of adiposity (obesity) or blood pressure 11.5 years postpartum.

Our study conducted on women with polycystic ovary syndrome (PCOS) showed that those women who did not have any increase in breast size during pregnancy had, as early as the first trimester of pregnancy, higher blood pressure, BMI, triglycerides and fasting insulin levels, compared to those with breast size increment. “No breast increment” was also associated with no or short-duration of breastfeeding. This study indicates that there might be factor(s) that affect breastfeeding, long before childbirth and the first attempts at breastfeeding.

These findings lead to the question whether breastfeeding per se has a causal impact on long-term maternal health, manifested as lower blood pressure, less obesity and less type 2 diabetes mellitus (T2DM), or whether other factors influence both the ability to breastfeed and the long-term health of the mother.

We use data from HUNT 1, HUNT 2, HUNT 3, UNGHUNT 2 and 3, and linked data from the Medical Birth Registry of Norway (MBRN). The study is funded by NTNU and St. Olavs hospital.