The reduction in blood pressure found in the study "is of clinically important magnitude and surprising," Dr. Lori Feldman-Winter told CNN in an email. Feldman-Winter, who was not involved in the study, is the chair of the American Academy of Pediatrics Section on Breastfeeding.
"I may have expected a difference to be apparent just prior to or during adolescence, but the fact that these differences were seen as early as three years of age indicates that breastfeeding participates in metabolic programming that spans the life cycle," wrote Feldman-Winter, who is a professor of pediatrics at Rowan University's Cooper Medical School.
The study, published Wednesday in the Journal of the American Heart Association, used data from almost 2,400 children who are part of the CHILD (Canadian Healthy Infant Longitudinal Development) Cohort Study. CHILD is a longitudinal study that tracks the health of thousands of Canadian mothers and their children born between 2009 and 2012.
The study analyzed data on the length of time infants were breastfed and compared it to their blood pressure at age 3. Across the board, breastfed children had lower blood pressure regardless of the amount of time spent breastfeeding.
The finding was unexpected, said senior study author Meghan Azad, deputy director of the CHILD Cohort Study, an associate professor of pediatrics and child health at the University of Manitoba in Winnipeg, Canada.
"We found, contrary to our expectations, it did not matter how long you were breastfed, whether it was two days, two weeks, two months or two years," Azad said. "We saw an improvement of blood pressure profiles from any breastfeeding at all."
Prior research shows extended breastfeeding from six months to over a year lowers an infant's risk of obesity, diabetes, gastrointestinal infections and more, according to the US Centers for Disease Control and Prevention. It also reduces the mother's risk of some cancers, diabetes and high blood pressure.
A "dose response" is often seen, meaning "the longer, the better" in relation to protecting against infections and asthma, Azad said.
The official recommendation from the American Academy of Pediatrics is to breastfeed exclusively for the first six months, then continued with complementary foods such as infant cereals, fruits and vegetables for a year or more.
The World Health Organization recommends the same for the first six months, with continued breastfeeding and complementary foods for up to two years of age or longer.
Previous studies attempting to examine the link between breastfeeding and children's blood pressure have been inconsistent, likely due to varying definitions of breastfeeding, the study noted.
Researchers for the current study categorized the children based on the duration of breastfeeding in the first days of life. One such category was "early limited breastfeeding," defined as breastfeeding that only occurred in the hospital.
Unlike previous research on the subject, Azad said the study was unique because they had this very detailed information about breastfeeding during the hospital stay after birth. This information allowed them to come to the conclusion that even breastfeeding only for the limited one to three days in the hospital is linked with lower blood pressure at age 3.
In these early days of breastfeeding, the mothers are producing colostrum, known to be especially nutritious and immunity-boosting for the infant.
"The first few days are really crucial," Azad said.
The reduction in blood pressure seen in the breastfed children is significant when comparing it to the levels of blood pressure in adults that are associated with lower risk of conditions such as hypertension and stroke, said lead study author Dr. Kozeta Miliku, a postdoctoral fellow at McMaster University in Hamilton, Ontario, Canada and a clinical science officer at the CHILD Cohort Study.
"The findings that we see on breastfeeding and blood pressure could be clinically relevant," Miliku said. "As a new mom-to-be, this research means a lot to me because it's important to understand that every drop counts."
Though any amount helps, sustained breastfeeding should still be supported, Miliku added.
Azad recognized different reasons women do not breastfeed: They may not be educated on its impacts, they may feel shamed from societal attitudes toward breastfeeding in public, and some may have clinical reasons for not breastfeeding, among other factors. These must all be acknowledged and tackled by policy makers and health care providers, she said.
In light of its findings, the study authors emphasized the need for immediate postpartum lactation support and increased education about breastfeeding to new and expecting mothers.
Similarly, Feldman-Winter said the study makes the case for policies that "work to improve maternity care practices that support breastfeeding initiation."
Azad and Miliku hope to continue following this cohort and monitoring whether these differences in blood pressure levels at age 3 impact the participants' health into adulthood. They also seek to learn more about colostrum and breast milk to understand why they are linked to reduced negative health outcomes.
For new mothers who are breastfeeding, the American Academy of Pediatrics recommends knowing the signs of correct nursing:
Incorrect nursing signs include your baby's head not being in line with their body, your baby is sucking on the nipple only but not on the areola and your baby's cheeks being puckered inward.
If you aren't hearing your baby swallow regularly or if you experience pain or nipple damage, you may want to seek advice from your pediatrician or or a lactation consultant such as La Leche League, a non-profit agency dedicated to providing education and support for breastfeeding mothers.
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