A new study finds that feeding infant girls soy formula may lead to severe menstrual pain when they become young adults. It’s the latest indication that soy formula in infancy may have harmful effects on the reproductive system.
The study found that women who were given soy formula as babies were 50 percent more likely to have experienced moderate or severe menstrual discomfort between the ages of 18 and 22, and 40 percent more likely to have used hormonal contraception to help alleviate menstrual pain. Earlier studies have linked soy formula to endometriosis.
The study, published online in the journal Human Reproduction, was conducted by scientists at the National Institute of Environmental Health Sciences (NIEHS), part of the National Institutes of Health, along with collaborators from Vanderbilt University Medical Center and the Henry Ford Health System. They examined data from 1,553 African-American women, aged 23-35.
Why would soy formula be so harmful?
The study’s lead author, Kristen Upson, Ph.D., said evidence points to genistein, a naturally occurring component in soy formula, which she said interferes with the development of the reproductive system, including factors involved in menstrual pain. She said these studies have also shown that developmental changes can continue into adulthood.
Upson’s earlier research linked soy formula feeding to endometriosis, and NIEHS senior scientist Donna Baird, Ph.D., has linked infant soy formula to larger fibroids among woman with fibroids and to heavy menstrual bleeding.
Other studies by NIEHS scientists found that girl infants fed soy formula had changes in the cells of the vagina, including differences in how specific genes are turned on and off.
A 2001 study by scientists at the University of Pennsylvania and the University of Iowa, which primarily included white young adults who participated in feeding studies when they were infants, also found an association between soy formula feeding and severe menstrual pain in the women.
“The results of both studies indicate that the findings may apply to all women, but further research is warranted before any changes are made to soy formula feeding recommendations,” said Baird in a news release. She noted that since the study is observational it is not able to show that soy formula causes the menstrual pain in adulthood, only that it is linked to it.
The American Academy of Pediatrics (AAP) promotes human milk as the ideal source of nutrition for infants. It does not recommend soy formula for babies born prematurely. For full term infants, the AAP recommends soy formula in rare cases where the child’s body cannot break down the sugars in milk or if the family prefers a vegetarian diet.
Upson said some estimates put the prevalence of menstrual pain in women of reproductive age at 60 percent. She added that menstrual pain can have a substantial impact on the quality of life, affecting school performance, work productivity, and relationships.
“Given how common menstrual pain is and the impact it can have on women’s lives, the next steps in research should examine exposures, even those that occur earlier in life that may increase a women’s risk of experiencing menstrual pain,” said Upson.