Then they measured the melatonin in the blood. They found that people exposed to light at night and day had low melatonin levels compared to those who were only exposed to light in the day.
The evidence becomes a little more wobbly in proving that Melatonin slows tumor growth. The evidence that Stevens based his theory on, involves pumping blood (high and low in Melatonin) through tumors implanted in rats. I am bothered that the rats had human blood pumped through human tumors. Who knows how the rats immune systems reacted to the foreign substances. Perhaps the rats even reacted to the Melatonin and let off hormones which slowed tumors, and that process would not happen in humans.
Perhaps it is true that shift workers do have a higher risk of cancer, and melatonin levels are suppressed in shift workers ,but they may not be related. We may have a correlation, but i’m skeptical we have causation. Still as Stevens says the theory is still only in a hypothesis stage and a basis for further study.
Structure of Melatonin