Is Breastfeeding Bad for Your Bones?

A new study shows that bone density declines the longer you breastfeed. But is there anything you can do about it and should this stop you from breastfeeding longer?

Is Breastfeeding Bad for Your Bones? Nina Buday/Shutterstock

You probably know that breastfeeding holds many benefits for baby as well as for mom—but there may be one downside to it. A recent study has found that the bone density in nursing women decreased the longer they breastfed. So what does this mean for your long-term bone health if you are breastfeeding?

Researchers at the University of Gothenburg in Sweden studied the bone density of 95 women from late pregnancy to 18 months after birth and compared them to a group of women who weren't pregnant or nursing. "We found that during the first four months postpartum, bone mineral density decreased in the hip, lumbar spine and shin bone, but only in women lactating at least four months," author Petra Brembreck, a researcher at the university's Sahlgrenska Academy who recently defended this study as her doctoral thesis, tells Fit Pregnancy. "Still at 18 months after delivery, bone mineral density in the shin bone was lower than shortly after delivery, but only in women lactating at least nine months. This was a new finding." The decrease in bone density Brembeck observed was as much as four percent.

The role of vitamin D

Brembeck originally thought that the levels of vitamin D, which is crucial for bone health because it helps the body absorb calcium, might be reduced with long periods of breastfeeding. Breastmilk generally lacks vitamin D because most women today don't get enough of it themselves to pass into their milk (which is why your pediatrician may recommend you give your baby vitamin D drops). But surprisingly, when Brembeck measured the women's vitamin D levels, no decrease was found. "We found no changes in vitamin D status during the first year postpartum, and no association between duration of lactation and changes in [vitamin] D during the first year postpartum," she says. "This has not been studied before."

So if a lack of vitamin D is not the reason breastfeeding moms' bones are weakening, what is, and what can be done to prevent it? "The major determinants for changes in bone minerals postpartum was body weight—a higher body weight was related to smaller decreases in bone minerals postpartum—and duration of lactation—a longer duration of lactation was associated with larger decreases in bone minerals postpartum," Brembeck says. "It appears that the longer women breastfeed, the more time it takes for the bone mineral density to return to values shortly after delivery or pre-pregnancy values." This could have something to do with the reduction in estrogen, which also helps protect bones, that occurs during breastfeeding.

How to prevent bone loss

But these results shouldn't lead you to stop breastfeeding early. "This does not mean that there is an increased fracture risk in later life in women with long duration of lactation. Most previous studies show that the bone minerals recover also in women with longer duration of lactation," Brembeck says. "We found that a higher total calcium intake, including both dietary intake and supplements, might be a protective factor against the postpartum bone changes," so you can help protect your bones during breastfeeding by getting enough calcium. Eat foods rich in it, including dairy products and some green vegetables, and talk to your doctor about how much extra calcium you should be taking.

In addition, exercise could help strengthen your bones while you're breastfeeding. "Generally, a higher mechanical load on the skeleton, such as exercise, strengthens the skeleton," Brembeck says, although her study didn't find an association between physical activity and changes in bone density.

More research is needed to look at the long-term effects of breastfeeding on moms' bone density, especially because Brembeck employed a new high-tech method called HR-pQCT to measure bone density levels. "Since HR-pQCT has not been used in postpartum women before, we cannot yet say anything about the clinical importance of theses findings," she says. "A longer follow-up period than 18 months is needed to evaluate if women with long lactation fully recover their bone minerals after weaning, or if the postpartum bone changes could potentially lead to an increased fracture risk in later life."