When most people think of serotonin they think of the link that it has to depression, and they also think that serotonin is chemical that is only used by the brain. While it is true that serotonin is essential to proper brain function, it is present in only small amounts in the brain–just 10%. The rest of the serotonin found in our body, that other 90%, is predominantly in the blood platelets, and in the digestive tract.
Serotonin is a neurotransmitter. That means that it is a chemical that helps to relay messages within the brain from one area to another. Because serotonin is found throughout our bodies, it is thought to be responsible for the proper functioning of not only psychological functioning, but also plays a large role in sleep, sexual desire, appetite, memory, learning, and body temperature regulation. Serotonin is a chemical that is not only necessary for the prevention of depression, but so much more.
Serotonin is made through a biochemical conversion process that allows certain cells in the body to change tryptophan into serotonin. You may have heard of trytophan with regards to sleep. Tryptophan is the chemical found in turkey that makes you want a long nap after Thanksgiving dinner. It is also found in dairy product, so that is why warm milk helps many to fall asleep. Nuts also contain tryptophan.
It is thought that low serotonin levels can lead not only to depression, but panic and anxiety, and excessive anger. Since serotonin levels in the brain cannot be measured by any test, the exact role that serotonin plays in depression and other problems can only be guessed at, and theories are based on hypothesis. Some believe that certain people simply do not produce enough serotonin, and are more inclined to suffer from depression as a result. Other researchers believe that some people to not have enough receptor sites in the brain to accept the serotonin that is available.
There is also a chicken or the egg discussion one whether low serotonin levels cause depression, or if depression leads to low serotonin levels. A blood test can measure the serotonin in the blood, and people with depression do have lower blood levels, but that doesn’t provide the answer to the which-came-first question.
There are drugs that effectively treat depression, the most common of which are called serotonin uptake inhibitors, or SSRI’s. You may recognize some of the names of these antidepressant drugs, which include Celexa, Lexapro, Prozac, and Paxil. It is thought that these drugs block the uptake of serotonin, which allows the body, which may be producing too little serotonin to begin, to build up levels to within normal limits, which will relieve depression. This takes time, of course, which is why it takes SSRI’s 6 to 8 weeks to reach peak effectiveness.
Some may be thinking about now that if they are depressed and need a serotonin boost that they should eat a whole bunch of turkey, or go on high protein diet. While this sounds good in theory, it won’t work. When your body is suddenly flooded with the amino acids found in protein, it gets overwhelmed, and cannot decide which to absorb, so it just doesn’t absorb any of them, including tryotophan. On the other hand, a large meal of carbohydrates will lead to high levels of trytophan in the blood, just waiting to be absorbed into the brain, which might lead to higher brain serotonin levels. This is why we tend to crave carbohydrates when we are depressed.
Since women experience depression more often than men, some may think that women have less serotonin than men. This is not true. Serotonin levels in men and women are almost identical. However, low serotonin levels create different reactions in men versus women. A man with too little serotonin tends to become impulsive, while a woman with too little serotonin will become depressed, or anxious. It is suspected that this difference is because of the difference in the hormones produced by men and women.
As you can see, serotonin is a mysterious body chemical that, when in low amounts, can cause all sorts of problems, depression being just one of them. Since most of what we know about serotonin and how it works is based on supposition, many studies are underway to better understand the mechanism of serotonin in the body. Once that is understood, strides can be made to better treat those with low serotonin levels, and to prevent the life altering problems caused by low serotonin levels.
Brunilda Navario, MD
Serotonin and Depression