Dubbed Mother Nature’s “feel good” chemical, serotonin is a natural body chemical messenger believed to perform most of its functions in the brain. Of all the brain chemicals, appropriate serotonin levels are probably the most important for maintaining an overall sensation of well-being. Serotonin is present in incredibly small amounts in the body and yet can create large numbers of problems when it is out of balance. It certainly impacts a host of functions, especially when there is a serotonin imbalance. Both males and females may experience serotonin deficiency although the edge here goes to females. Studies in Sweden have shown that while female brains have a greater number of the most common serotonin receptors (as compared with males), woman also have lower levels of the protein that transports serotonin back to the nerve cells that secrete it. The serotonin system in healthy woman, so called, also appears to differ from that in women with serious premenstrual mental symptoms (e.g., they don’t seem to respond as flexibly to the hormone swings of the menstrual cycle). Different types of serotonin receptors appear to be present in the brain, as well. Some are associated with migraine headaches, others with the motility of food in the intestines. Some researchers say that when sunlight enters the eyes a signal is sent from the eye to the brain to make more serotonin, which helps explain the reason people sometimes feel gloomy when the weather is cloudy and rainy. Pretty impressive little chemical, serotonin.