That was the finding of a recent study that has been reported by the media in recent days.
The NHS have provided some interesting information about the research itself. Several questions came to mind whilst reading all of this.
Firstly, the study found that women who do not breastfeed were more likely to have heightened androgen levels. It has been suggested this could be because testosterone inhibits milk production, and women who have higher levels may have less desire to breastfeed in the first place. I find this extremely simplistic. Norway is a country where 99% of women initiate breastfeeding, so culturally things are different there to the UK or the US, where they are many, many reasons why a woman may choose not to breastfeed, including lack of support from family, friends or health professionals, bad advice given, social reasons, unsupportive employer/little to no maternity leave, history of sexual assault or abuse, etc.
It also does not take into consideration mothers that have intense struggles with breastfeeding yet doggedly persevere with it.
To really examine whether poorer health among formula fed infants is due to the formula or higher levels of androgens in the mother's body before birth, they needed to compare health outcomes between babies whose mothers that formula fed because of medical inability to breastfeed with women that formula fed by choice or for reasons such as work constraints and sabotage that would have otherwise been able to successfully breastfeed.
Secondly, I feel this research could be very useful in potentially identifying potential breastfeeding issues pre-birth by testing hormone levels and then offering them additional support and help to enable them to breastfeed. To make the jump to "Formula milk is as good as breastmilk" is vastly irresponsible and would do mothers and babies a disservice.