> “Worse insomnia, depression/anxiety or the use of other sleep-enhancing medicines might be linked to both melatonin use and heart risk,” Nnadi said. “Also, while the association we found raises safety concerns about the widely used supplement, our study cannot prove a direct cause-and-effect relationship. This means more research is needed to test melatonin’s safety for the heart.”

This seems pretty critical, no? I would assume that melatonin use increases with the severity of insomnia, and persistent lack of sleep has a whole host of long-term health implications. So insomnia a priori seems highly likely to cause both increased melatonin consumption and heart disease. Given how obviously confounded this causal system is, it's practically negligent to not at least control for severity of insomnia or something. Ideally they should have done a matched study or DID or something, but without any attempt to account for the confounding this study is just clickbait.