Outdoor light can reach 3000 lux on a bright sunny day. Researchers in Finland found that rats who were exposed to natural daylight had significantly higher evening melatonin levels than another group of rats who had an equal amount of exposure to artificial light. Evening light suppresses melatonin production in humans. In Western nations, the habit of staying up late at night is generally associated with significant amounts of light exposure during those hours. From the standpoint of melatonin production, it would be better to go to bed early.
Research suggests that controlling stress can improve melatonin production.
It cut melatonin production in half for 6 hours. Alcohol also depresses melatonin levels. An early study by Carr and colleagues looked at seven healthy persons. They demonstrated that one hour of exercise on a stationary bicycle could double or triple melatonin levels. Other studies have also demonstrated that physical exercise can boost melatonin levels.