I remember one classic one is the "no coffee when pregnant", the study says this causes problems, the test was performed on rats and by feeding them coffee in the amount of 3/4 of their body weight. We can agree that with this amount, it's reasonable it could cause problems. Very different from one cup of coffee though.
The other study that was done is about Amniocentesis, this one is more interesting the chance of miscarriage is considered 0.1% but this was before the operation was performed with a live ultrasound to look at the needle while performing it, which (probably) makes a big difference. Before, doctors performed an ultrasound and then went in blind.
There was also a serious bias towards a certain type of population. But of course doctors don't bring this up at all.
Last thing is sids, it's a terrible type of diagnosis that pushes parents against the instinct of sleeping with their children, even though this is commonly done in non-western cultures and can save a lot of pain to the parents and give a lot of security to the child. Do your research though, medical community reports risks and I'm no doctor, just a dad who read a few books.
Glad my children are healthy. Every time I read about some illness for children I feel an incredible weight on my heart
Honestly I don't know which study you're talking about, and I'm not trying to question what you're saying (such studies indeed often use exaggerated amounts because it's more likely to show effects, but it can skew the results of course) but I just found it interesting that depending on what "feeding them coffee in the amount of 3/4 of their body weight" means, well over a pregnancy it's easy to consume 3/4 of one's body weight in coffee.
It means about 150 mL coffee per day for a woman weighing 55 kg, over 9 months.
About SIDS and sleeping with the children in the same bed, if I remember correctly (it's been some time since I had to read about this) the very large majority of cases happened with parents who either smoke or are obese. I think I couldn't find precise stats just for non-smoking, non-obese parents but it seems like SIDS basically didn't happen in this case when co-sleeping. It also almost never happens with immigrant parents for some reason (even though they are statistically more likely to practice co-sleeping, here in Europe).