The Influence of Serotonin on Personality, Career, and Longevity

Serotonin (5-hydroxytryptamine) is an indole derivative, abbreviated 5-HT, with the chemical formula C10H12N2O, and is converted from tryptophan. It was first discovered in blood serum, hence the name serum tonin. Serotonin is widely present in mammalian tissues and is highly concentrated in the cerebral cortex and within nerve synapses. It is a monoamine and an inhibitory neurotransmitter that influences the personality of humans and animals.

People with excessively high serotonin levels in the brain often tend toward obsessive-compulsive traits: they like tidiness, are cautious and meticulous, and can even be somewhat neurotic. Those with very low brain serotonin tend to be impulsive and depressed; impulsive violent offenders and suicide victims usually have low serotonin levels.

The antidepressant Prozac (fluoxetine) acts through the serotonin system. Prozac selectively inhibits the serotonin transporter, blocks presynaptic reuptake of serotonin, and prolongs and enhances serotonin's action, thereby producing an antidepressant effect.

Prozac is often used by psychiatrists to treat depression and its accompanying anxiety, and is especially suitable for late-life depression. It can also treat obsessive-compulsive disorder (though the dose should be correspondingly increased), bulimia nervosa, panic disorder, and generalized anxiety disorder.

Serotonin is often nicknamed the "happy gene." When brain serotonin is relatively high (not excessively high), a person tends to be an optimist. Compared with average people, those with higher serotonin are less neurotic and more easygoing—and this difference is independent of sex, race, education, and income. Such people are the proverbial "joy bringers": easily content, feeling good, and always spreading happiness. Famous optimists in history such as Su Dongpo, Tao Yuanming, and Zhuangzi probably all belonged to the high-serotonin type.

On human chromosome 17 there is a serotonin-related gene called the serotonin transporter gene. Upstream of this gene is an activation sequence: a 22-base sequence repeated 14 times (short allele) or 16 times (long allele). About one-third of people carry two copies of the long allele, which makes them slightly less efficient at shutting down gene expression; this means they have more serotonin transporters and higher brain serotonin levels.

So some lucky people are born optimists. No matter what family a person is born into, as long as he carries this long allele he is more easily happy and content than others. Such people are truly blessed by heaven; without striving as others do, they can still attain great well-being. I myself may be one of these lucky ones: my mother and I are both natural optimists, able to live carefree even in utter poverty, and I may have inherited this gene from her.

Serotonin can produce melatonin. Some depressed patients are hypersomnic, related to excessive conversion of their serotonin into melatonin. If a person is unusually sleepy, it deserves attention. Interestingly, one of the main symptoms of TCM lesser-yin syndrome is "but desire to sleep" (listlessness and somnolence), which resembles depression. I have treated cancer patients with depressive symptoms who were drowsy and fatigued using Mahuang Fuzi Gancao Tang (Ephedra, Aconite, and Licorice Decoction), the TCM treatment for lesser-yin syndrome, with some effect.

Other depressed patients may have inherently too little serotonin, depriving them of the raw material for melatonin, and therefore become irritable and unable to sleep. I have treated such insomnia, described as "vexation in the heart and inability to sleep" due to lesser-yin yin deficiency, with Huanglian Ejiao Jizihuang Tang (Coptis, Ass Hide Glue, and Chicken Yolk Decoction), also effectively. Jizihuang is egg yolk, a high-cholesterol food; a high-cholesterol diet raises brain serotonin levels.

The above experience is offered for reference. The medical and pharmacological reasoning I propose for Mahuang Fuzi Gancao Tang and Huanglian Ejiao Jizihuang Tang is only my own speculation and requires further research and stronger data.

Many people like snacking, partly because of serotonin. Eating carbohydrate-rich snacks quickly prompts the pancreas to secrete insulin; rapid insulin secretion carries more tryptophan to the brain, where tryptophan is converted into serotonin, producing a pleasurable feeling. Some depressed patients have a tendency to binge eating because bingeing relieves depression.

Drugs and diets that lower blood cholesterol (low-cholesterol diets) have the opposite effect: they lower brain serotonin, making people more impulsive and depressed, and prone to antisocial acts. Pooling all findings, researchers found that while cholesterol-lowering treatment reduced the risk of heart disease by 14%, the risk of death by violence rose markedly by 78%.

So treating high-cholesterol patients carries certain risks, and people with normal cholesterol are not suited to low-cholesterol diets for weight loss either. Cholesterol is not the lower the better: people with below-normal cholesterol tend to have extreme personalities, be impulsive and depressed, be aggressive, and face higher risks of suicide and violent crime. Those with very low cholesterol are four times as likely to commit suicide as those with higher cholesterol.

Higher serotonin levels make people see the positive side of things. The writer Franz Kafka had a classic line—"Every difficulty can defeat me"—which is typical language of someone with low serotonin, who tends to see the negative side. For those with high serotonin, this saying would usually be revised to: "My fate is ruled by me, not by heaven," or "I can overcome every difficulty."

Because of their positive mindset, high-serotonin people also tend to be more successful in their careers and live longer. Having dealt with all kinds of cancer patients for years, I find that among cancer patients, those who are relatively active (not extreme) in associations or online—often the leaders or spiritual leaders of such groups—live longer, because these people belong to the high-serotonin type. When struck by cancer, low-serotonin people collapse quickly, while high-serotonin people face it optimistically and respond actively.

Serotonin is related to human social relationships and status. Animal experiments show that monkey leaders have high serotonin levels, but when a leader is pulled down and controlled by other monkeys, its serotonin drops sharply. Experiments in university student clubs show that club leaders have high serotonin, but after being removed from office their serotonin falls accordingly. This may explain why some people have such a strong lust for power, because holding power really does make people happier. Generally speaking, the stronger the self-esteem and the higher the social status, the higher the serotonin level.

Many people in power or academic elites become more depressed after retirement. The classic case is Australia's oldest scientist, 104-year-old Professor David Goodall: after being dismissed by the university for being too old, he fell into depression and ultimately chose euthanasia. If he could have continued working at the university, he might not have chosen this path. That is why I often urge cancer patients to return to society and to work.

The finding that social behavior can alter serotonin overturned most people's existing biological worldview. Once people discovered that social relationships and social status can change serotonin levels, they were no longer controlled by "biological determinism" and "genetic determinism"; depressed people can improve their symptoms by raising their social status and changing their social relationships. In fact, many emotionally depressed people become lively and cheerful in religious groups and charitable social organizations, because they gain recognition there.

For most people, social recognition is an important route to happiness. Professor Seligman, the father of positive psychology, found that those who gain social praise through public causes become happier than before; so the folk saying "helping others brings joy" conforms to biological law. Beyond that, doing work one loves and spending a lifetime with a beloved partner both raise brain serotonin, and such people also tend to find happiness.

Of course, more serotonin is not always better. As noted, people with excessively high serotonin are prone to obsessive-compulsive disorder. Excessively high serotonin excites the sympathetic nervous system while inhibiting the autonomic nervous system, producing a range of autonomic symptoms such as palpitations, chest tightness, fatigue, sweating, dizziness, headache, insomnia, anxiety, irritability, depression, abdominal pain, diarrhea, or constipation.

In recent years some scholars have also detected excess serotonin in the serum of liver cancer and cirrhosis patients, and some have even suggested serotonin as a tumor marker for liver cancer. The excessively high serotonin in liver cancer patients may be related to cholesterol, though relevant research has not yet received general academic attention.