The new method provides insight into how women's bones are permanently altered after childbirth

A team of anthropologists has discovered that reproduction permanently alters a woman's bones
in a way never before possible.
The findings, based on an analysis of primates, offer new ideas
about how fertility can permanently alter the body.

"Our findings provide additional evidence that reproduction has a profound effect on the female organism, further demonstrating that bone is not a static organ, but a dynamic organ that changes with life events," explains Paola Cerrito, a doctoral student in New York University's Department of Anthropology and School of Dentistry, who led the study
.

Specifically, the researchers found lower
concentrations of calcium, magnesium and phosphorus in females who had experienced reproduction.
These changes are related to
the birth itself and lactation.

However, they caution that while other clinical studies have shown calcium and phosphorus to be necessary for optimal bone strength, the new findings do not address the overall health effects
in primates or humans.
Instead, they say, the work reveals the dynamic nature
of our skeletons.

Shara Bailey, an anthropologist at New York University and one of the study's authors, points out: "Bone is not a static and dead part
of bone.
It constantly adjusts and responds to
physiological processes.
”

The study's other authors, published in the journal PLoS ONE, are Timothy Bromage, a professor at New York University School of Dentistry, Bin Hu, an adjunct professor at NYU School of Dentistry, Justin Goldstein, a doctoral student at Texas State University, and Rachel Kalisher
, a doctoral student at Brown University.

The claim that menopause has an effect on a woman's bones has long been proven
.
What's less clear is how pre-life cycle events, such as reproduction, can affect bone composition
.
To solve this problem, the researchers studied primary lamellar bone, the main type of
mature bone.
This part of the bone is an ideal examination site for the human body because it changes over time and leaves biomarkers of these changes that allow scientists to monitor changes
over the life cycle.

In the PLoS ONE study, researchers examined the rate of lamellar bone growth in
femurs or thigh bones of female and male primates who lived and died naturally at the Sabana Seca Field Station in Puerto Rico.
Veterinarians at field observatories monitor and record information about the health and reproductive histories of these primates, allowing researchers to match
changes in bone composition to life events with astonishing precision.

Cerrito and her colleagues used electron microscopy and energy-diffuse X-ray analysis, a common method for measuring the chemical composition of tissue samples, to calculate changes
in calcium, phosphorus, oxygen, magnesium and sodium concentrations in primate bones.

Their findings showed that women who gave birth had different
concentrations of certain elements in their bodies compared to women who did not have children.
Specifically, in women who give birth, bones formed during reproduction are lower
in calcium and phosphorus.
In addition, magnesium concentrations decreased
significantly during the feeding of infants by these primates.

"Our study shows that bones respond dynamically to changes in reproductive status even before they stop having children, and in addition, these findings reaffirm the significant impact of fertility on the female organism – quite simply, evidence of reproduction is 'written on the bones of life'"
.

The femur images analyzed in this study are available for download
from Google Drive.