Study co-author Mary C. Noonan, an associate professor of sociology at the University of Iowa, and Phyllis L.F. Rippeyoung of Acadia University in Canada, said many breastfeeding proponents argue breastfeeding has financial advantages over formula-feeding because it is free.
"Breastfeeding for six months or longer -- the time mothers are recommended they breastfeed for a minimum -- is only free if a mother's time is worth absolutely nothing," Noonan said in a statement.
The study involved a nationally representative sample of 1,313 first-time U.S. mothers, who were in their 20s or 30s when they gave birth between 1980 and 1993 and were employed in the year before their first children were born.
The study published in the American Sociological Review found the long-duration breastfeeders sacrificed considerable income after giving birth compared to short-duration breastfeeders and formula-feeders, largely because long-duration breastfeeders were more likely to switch to part-time work or to leave the workforce entirely.
"When people say breastfeeding is free, I think their perspective is that one doesn't have to buy anything to breastfeed whereas one needs to purchase formula and bottles to formula-feed," Rippeyoung said. "But, this simplistic view doesn't take into consideration the hidden cost: the substantial income women often lose when they breastfeed for a long duration. To me, I see it as being highly related to how women's unpaid work has always been undervalued."
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