Breastfeeding’s impact on bone density could boost development of osteoporosis drugs

Pregnancies do not weaken a woman’s skeleton. Breastfeeding, however, can reduce bone density considerably. These are findings from a research report produced at Lund University in Sweden. But breastfeeding women need not worry.

“There is a dip, but the body is absolutely fantastic at making up the loss,” says Kristina Åkesson, professor of orthopedics.

Breastfeeding and pregnancy both require large amounts of calcium. That is why Lund University researchers Lisa Egund and Åkesson wanted to examine how the reproductive cycle affects the bone density of women. The study followed 750 women over a ten-year period to investigate the effect of pregnancy and breastfeeding on the skeleton.

The women were 25 years old when the study began—an age when bone density is normally highest. Ten years later, the data was collected: How many had been pregnant and had children? If so, how many children? Were the children breastfed, and if so for how long?

“The participants filled in an extensive form and part of the survey covered reproductive health. We also collected lifestyle-related information on physical activity, alcohol consumption, smoking and BMI,” says Egund, Ph.D. in Orthopedic Science, Lund University, and senior physician at the Orthopedic Department, Skåne University Hospital.

With some surprise, the researchers noted that pregnancy—one or more—did not impair the bone density of the skeleton. A short time after the pregnancy, a small difference could be seen, but among women who did not become pregnant again for three years, a difference was no longer evident.

However, among breastfeeding women it was clear that the skeleton was affected.

“Where six months or less had passed since they stopped breastfeeding, we saw a difference in bone density of 7%, which in this context is a lot,” comments Egund.

Fortunately, bone density recovered over time—and the more time that passes after breastfeeding, the more bone density returns to normal. After two years, it proved to be even slightly better than before breastfeeding.

“The study is unique in this respect. Previous studies have measured bone density for a short period after the birth or after a long time has passed, several decades later. Our study, which in international terms is much larger, fills a knowledge gap regarding the effect on the skeleton of pregnancy and breastfeeding among young women. This will enable future comparisons,” says Professor Åkesson.

The researchers measured bone density throughout the skeleton, but it is in the hips that the biggest reduction was noted. However, the orthopedists emphasize that the reduction is not felt and entails no risk of a broken hip.

Åkesson is positively surprised that the recovery is so fast.

“If we understand these mechanisms, we can use that knowledge to develop more potent drugs against osteoporosis. We also hope, of course, that the results have a positive effect on women’s choices regarding breastfeeding.”

The next step in this long-term study is to see what happens to the same women over the next ten years, from the age of 35 to 45.

“We think the skeleton’s recovery is the same during that period. The skeleton has a fantastic ability to remineralize itself,” says Åkesson.

The study was recently published in the Journal of Bone and Mineral Research.