(Reuters Health) - Feeding infant girls baby formula containing soy may set them up for more painful menstrual periods as young women, a new study suggests.

The research, which included information on more than 1,500 African American women, reinforces findings in earlier studies that included mostly Caucasian women.

“We observed that soy formula feeding during infancy was associated with several indicators of severe menstrual pain in reproductive age women,” said Kristen Upson, a postdoctoral fellow in the epidemiology branch at the National Institute of Environmental Health Sciences (NIEHS) in Research Triangle Park, North Carolina.

“This included a 40 percent increased risk of ever using hormonal contraception for menstrual pain and a 50 percent increased risk of moderate to severe menstrual discomfort with most periods during adulthood,” Upson noted.

The researchers analyzed data from 1,553 African American women who live in Detroit and who have been participating in a larger NIEHS study of environmental health effects. The women were all aged 23 to 35 when they enrolled in that study, which was designed to look at risk factors for developing benign uterine tumors, called fibroids. All were free of fibroids at the start of the bigger study.

At the start of the study, women were all asked to complete and return by mail an early-life survey that included questions for their mothers on early-life exposures. If the mothers weren’t available, the women were instructed to ask a relative or a close friend of the mother.

Among the questions, women were asked whether they had been fed soy formula as a baby (yes or no), how long they had been fed soy (less than a month, one to three months, four to six months), and whether the soy was introduced during the first two months after they were born (yes or no).

Overall, researchers found that women who had ever been fed soy formula as babies were, at ages 18-22 years, 50 percent more likely than those not fed soy to experience moderate or severe cramping during most periods when they were not using hormonal contraception.

Women fed soy as babies were also 40 percent more likely to have used hormonal contraception at some point to alleviate menstrual pain, the study team reports in Human Reproduction.

While the results don’t explain why soy formula might be linked to painful cramping during menses, Upson has some theories. “The link between soy formula feeding in infancy and menstrual pain in adulthood may be biologically plausible given that in the early months after birth, an infant’s reproductive system continues to develop and an infant’s nutrition primarily consists of breast milk and/or formula,” Upson said in an email.

“This can lead to a substantial exposure to the components in formula, including phytoestrogens (plant compounds that are structurally similar to estrogen) in soy formula during a critical window of development.”

There’s some evidence of what can happen from animal models, Upson said. “Data from animal studies have shown that genistein, one of the phytoestrogens in soy formula, given after birth has effects on the development of the reproductive system that persist into adulthood, including the parts of the reproductive system involved in menstrual pain.”

While the new research won’t help women already experiencing severe cramping, Upson hopes that it will prevent another generation of women from developing the same problem.

“Given how common menstrual pain is and the impact it can have on women’s lives, our findings point to the need for a greater understanding of exposures, even those that occur earlier in life, which may increase a woman’s risk of experiencing menstrual pain,” she said. “This information can be used to inform prevention efforts to improve women’s health in the future.”

SOURCE: bit.ly/2AXXFzk Human Reproduction, online November 9, 2018.