Serotonin is a neural chemical that is responsible for sending signals across the brain. Though this type of neurotransmitter is synthesized in the brain, where its major functions are performed, about 90% of serotonin supply is found in digestive tract and blood platelets. It is estimated that an average adult body has five to 10 milligrams of serotonin.
Serotonin Production
Serotonin is synthesized through a unique biochemical conversion process involving tryptophan, the building blocks of proteins. Tryptophan hydroxylase is used by serotonin-producing cells along with tryptophan to form serotonin, otherwise known as 5-hydoxytryptamine.
How Serotonin Affects Health
A neurotransmitter facilitates the transmission of messages from one brain region to another. Cells of neurotransmitters like serotonin are widely distributed, thus they are assumed to be capable of affecting psychological processes and physiological functions. Serotonin directly or indirectly influences most of the 40 million brain cells, such as those responsible for mood changes, sexual urge, sleep, memory, appetite, temperature regulation, cognition, and some social behavior.
Serotonin can affect the functioning of muscles, heart, and several components of the endocrine system. Research data reveal that there is a correlation between serotonin production and level of milk production in the breast and likelihood of sudden infant death syndrome (SIDS).
How Serotonin Causes Depression
Many scientists are linking abnormal production or transmission of serotonin to mood problems that lead to depression. Depression may be caused by underproduction of serotonin in the brain, lack of serotonin receptor sites, failure of serotonin to reach receptor sites, or low level of tryptophan, the building blocks of serotonin. Any one of these abnormalities can lead to psychological problems other than depression, such as obsessive-compulsive disorder, panic, too much anger, and anxiety.
One of the newest theories on the pathology of depression attributes the disease to poor brain cell production. This theory emphasizes the link between depression and serotonin, as the neurotransmitter regulates brain cell production. Antidepressant medications like Prozac, Celexa, Lexapro, and Paxil work by increasing the level of serotonin, which in turn stimulates the synthesis of brain cells.
Despite the popularity of the theory that links low serotonin level and depression, there has been no research conducted to prove that serotonin deficiency causes depression. Serotonin level in the brain cannot be measured, and even if blood test shows that serotonin count is lower in depressed people, it does not confirm whether serotonin deficiency causes the depression or whether the depression causes serotonin deficiency.
The mechanism underlying antidepressant medications that work on serotonin levels, namely selective serotonin reuptake inhibitors (SSRIs) and serotonin and norepinephrine reuptake inhibitors (SNRI), are not fully understood, though they are believed to be effective in alleviating the symptoms of depression.
Food and Serotonin Level
Foods can indirectly affect the level of serotonin in the body. Unlike nutrient-rich foods, which can directly boost the level of nutrients in the body, there are no foods that can directly increase serotonin supply. Serotonin-stimulating foods work by increasing the level of tryptophan, the amino acid that constitutes serotonin. Trytophans are found in protein-rich foods such as meat. Dairy foods, nuts, and fowl are also good sources of trytophans. Ironically, both tryptophan and serotonin levels will decrease if a protein-packed meal is eaten. Too much amino acid in the bloodstream will restrict the entry of tryptophan into the brain. If only a small percentage of tryptophans reach the brain, serotonin production is unlikely to increase significantly.
To prevent other amino acids from competing with tryptophan on its way to the brain, eat carbohydrate-rich foods. This will stimulate the production of insulin, causing amino acids other than tryptophan to be absorbed by the body, but not by the brain. This means that tryptophan will remain at high levels in the bloodstream. Consequently, tryptophans will travel smoothly to the brain, prompting the production of more serotonin.
Another way to boost serotonin level is to take more vitamin B-6, which causes tryptophan to be converted to serotonin faster.
Exercise and Serotonin Level
Scientific findings showed that exercise can be as effective as antidepressants and psychotherapy in elevating mood. Recently, researchers at the University of Texas at Austin have disproved the old belief that depressed people need to do several weeks of exercise before they can notice improvements in depression. The researchers reported that just 40 minutes of exercise could elevate mood.
Given these conflicting claims, the anti-depression effect of exercise warrants further investigation. While some attributes the mood elevating effect of exercise to its possible role in serotonin regulation, to date there are no scientific data available to back this claim.
Gender Differences in Serotonin Levels and Behavioral Response
Scientific data show that men’s serotonin level is slightly higher than that of women, though some suggest that the difference is negligible. However, a study published in “Biological Psychiatry” suggested that men and women respond very differently to reduction in serotonin. This may explain why women are more vulnerable to depression than men.
The study examined behavioral changes among male and female subjects in response to tryptophan depletion. Men were found to be more compulsive, though not necessarily depressed when serotonin level in the brain was decreased. On the other hand, women showed significant mood decline and became more cautious. These responses are commonly associated with depression. While there seemed to be no notable difference in serotonin process in both sexes, researchers suggested that each sex used serotonin differently.
While sex-specific serotonin research is still in its infancy stage, a number of researchers are expressing interest in the differences in the way each sex responds to the decline in serotonin level. Gender-specific research on such response may explain why anxiety and mood disorders are more common in women, while ADHD, impulse control disorders, and alcoholism are more common in men.
There are scientific data suggesting that the interaction of female hormones and serotonin causes some symptoms to occur or worsen during premenstrual and postpartum periods or around menopausal age. Sex hormones are at high levels during these three periods. Unlike women, men generally have steady level of sex hormones until middle age, which marks the gradual decline of hormonal levels.
Serotonin Deficiency Among Dementia and Alzheimer’s Disease Patients
It seems that serotonin at least plays a role in memory-related problems. Several researchers propose that serotonin level, like bone mass, decreases with age. A scientific paper published in 2006 cited cases of serotonin deficiency in brains of Alzheimer’s patients. This deficiency may be the result of reduction in receptor sites, the cells that receive serotonin. To date there is no proof that serotonin-increasing therapy will work with Alzheimer’s disease or dementia. However, future research may establish the relationship between serotonin and memory loss.
Serotonin Syndrome
Serotonin syndrome is a rare side-effect of SSRI antidepressants. These drugs are generally safe, though its serotonin-increasing effect seldom leads to health complications. Serotonin syndrome is marked by extremely high level of neurochemicals in the body. This happens often when two or more antidepressants and other serotonin-increasing drugs are taken simultaneously. For example, anti-migraine medicines like Triptans, when taken with an SSRI drug for depression, are likely to boost serotonin level beyond normal limit. Serotonin overload is to be expected also when St. John’s wort and other SSRI supplements are taken along with other serotonin drugs.
Serotonin syndrome is to be expected when you first start a medication or increase the dosage. Combining older depression medications (called MAOIs) and recreational drugs like ecstasy or LSD with SSRIs should also be avoided to prevent serotonin syndrome.
Common symptoms of serotonin syndrome are hallucinations, restlessness, vomiting, rapid heartbeat, rise in body temperature, sweating, nausea, poor muscle coordination, diarrhea, spasm, and abrupt changes in blood pressure.
Serotonin syndrome seldom happens, but this condition could be dangerous and lead to medical emergency. Treatment includes drug withdrawal, muscle relaxers, IV fluids and serotonin blockers.
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