It is not possible to prove an assertion of non-existence, in this case the non-existence of risk. These faux-studies are just taxpaid grant drains for underemployed clinicians.
Proof of non-existence requires examination of the entire universe of discussion. In a fractally complex reality (after Taleb and Mandelbrot) that is not possible, there is always Taleb's BLACK SWAN.
He tells the Thanksgiving Turkey story; for 1000 days the farmer feeds the turkey, each feeding a datum in the turkey's confidence in Utopia. On the 1001 day the turkey meets his BLACK SWAN - the axe!