Of course, that's assuming that those genes don't influence anything else. As an editorial accompanying this study points out, this is an important caveat for all Mendelian randomization studies. "For example," psychiatrist Adam Chekroud writes, "if the exercise gene variants also relate to low energy, and low energy relates to depression, this relationship would represent another path through which exercise gene variants might affect depression risk." But he goes on to note that the study authors were aware of this potential misstep and did everything they could to minimize it. Even after removing genes associated with traits like body mass index or education level from the equation, their finding still held.