There is indeed a lot of evidence of this but you've got the direction backwards- it's not that women avoid studies, it's that for a long time studies specifically excluded women. Ditto for people of different races. This is why these days (well, as of today, at least) the NIH has a whole set of very well-established policies around inclusion in clinical trials that include sex, race, and age: https://grants.nih.gov/policy-and-compliance/policy-topics/i...

And this isn't for "DEI" reasons, it's literally because for decades there used to be drug trials that excluded women and as a result ended up releasing drugs that gave half the population weird side effects that didn't get caught during the trials, or just plain didn't work as well on one group or another in ways that were really hard to debug once the drug was on the market. That was legit bad science, and the medical research world has worked very hard over the last thirty years to do better. We are admittedly not there yet, but things are a lot better than they used to be.

For a really interesting take on the history of racial exclusion and bias in medicine, I recommend Uché Blackstock's recent book "Legacy: A Black Physician Reckons With Racism In Medicine" which gave a great overview.

Oh! And also everybody should read Abby Norman's "Ask Me About My Uterus," it gives a fabulous history of issues around women's health.