Finally wrangling with the complexity of female bodies benefits us all

Women aren’t just “little men”. And yet, it has long been convenient for medical science to act as if they are, focusing studies on male rodents and men because they lack the complicated hormone cycles of females, and then transferring any findings over onto women. Thankfully, in recent decades, there has been widespread acceptance that neglecting the study of female bodies in this way has harmed women’s health, by producing treatments that don’t work as well for them as for men.

Now, studying how sex chromosomes shape our immune systems has brought a further twist to the story – ignoring the complexity of female bodies hasn’t just hurt women, but everyone (see “Women have supercharged immune systems and we now know why“).

Much of the problem comes from the power of averages. Statistical tools give us the ability to smooth out variation and draw powerful discoveries from data. But when overused, they erase signals that have much to teach us. Women typically have stronger, more responsive immune systems than the average man, showing, for example, more durable responses to vaccines and lower rates of death from infectious diseases in older age.

But by lumping male and female participants together in medical research trials – admittedly better than not studying women at all – sex differences in response to antiviral drugs and new vaccines have been blended and lost. This can ultimately lead to the average woman receiving too high a dose of a drug, at the same time as the average man is given too little for optimum treatment. Research into how these differences might affect transgender people has received even less attention.

Finally though, researchers are unpicking how the X chromosome and hormones underpin these sex differences, and the insights from this work should enable us to better personalise treatments for everything from long covid to cancer – and for everyone. We all benefit from abandoning the concept of “little men”.