Very unlikely these ominous correlations regarding melatonin supplementation have any clinical validity. In supplement form, melatonin has a half-life of only a few hours. As little as 0.33mg melatonin has found to be effective to trigger sleep, especially if taken at night and surroundings are dark. That’s basically what it’s good for, because of the half-life, the effect wears off a few hours later, with natural circadian rhythm ending endogenous melatonin production and ramping up cortisol as dawn approaches. Melatonin is not a sleeping pill. If use of the supplement is keep to minimally effective doses, adverse effects are probably close to zero.