¡Hágase la luz! Aprovechar al máximo su serotonina y melatonina
Los seres humanos evolucionaron viviendo al aire libre, expuestos a la luz natural brillante durante el día y a la oscuridad total durante la noche. Los sistemas de nuestro cuerpo dependen de la luz natural para mantenernos saludables; nuestros ojos y piel realmente necesitan estar expuestos a la luz del día para que nuestros cerebros y cuerpos funcionen de manera óptima. También necesitamos la oscuridad, para que nuestro reloj circadiano pueda regular nuestro ciclo de sueño y otras funciones corporales.
Yet sadly, a 2019 study showed that we spend just 2% of our time (94 minutes per week) outdoors. And it’s not just adults; children spend just 4 hours per week playing outside.
Spending our lives indoors has led to increasing rates of depression, poor cardiovascular health, nearsightedness, asthma, and insomnia. Childhood rates of mental illness, nearsightedness, asthma, and poor cardiovascular fitness have increased significantly in recent years as well, and children reportedly experience symptoms of seasonal affective disorder during summer months simply because they spend most of their day indoors.
Parte de la razón del aumento de estas condiciones es que necesitamos la exposición a la luz del día para producir la serotonina adecuada, un neurotransmisor involucrado en una amplia gama de procesos fisiológicos. Y la serotonina es el precursor de la melatonina: se convierte en melatonina en la oscuridad. La melatonina es necesaria para regular nuestro ciclo de sueño-vigilia, así como nuestro sistema inmunológico. Si no pasa tiempo al aire libre todos los días, es probable que su salud se vea afectada por ello.
En esta publicación, hablaré sobre lo que hacen la serotonina y la melatonina en nuestro cerebro y nuestro cuerpo, cómo las producimos, qué sucede cuando sus niveles son bajos y cómo aumentar naturalmente la serotonina y la melatonina.
¿Qué es la serotonina y cómo la producimos?
La serotonina es un neurotransmisor que ayuda a regular el estado de ánimo, el comportamiento social, el aprendizaje, la cognición, la memoria, la función cardiovascular, la función sensoriomotora, la sensación de dolor, el apetito, la motilidad intestinal, el control de la vejiga, el sueño y el deseo sexual. ¡Uf!
Serotonina is found in the central nervous system, blood platelets, and the mucosa of the gastrointestinal (GI) tract. Approximately 95% of our body’s serotonin is in our gut. Enterochromaffin cells in our gut lining release serotonin, which regulates peristaltic waves (movements of muscles that move food through our digestive tract) and enzyme secretion. Our gut produces the serotonin that it needs locally. So if you have any issues with gut motility, you should make healing your gut a priority; a healthy gut is necessary in order to produce healthy levels of serotonin.
Figures 1 and 2 from The Expanded Biology of Serotonin, marzo 2018.
The brain also produces the serotonin that it needs locally. Serotonin is produced in the brain by the raphe nuclei in the brainstem, as shown in Figure 1 above. When bright light enters the eyes, retinal ganglion cells send signals to serotonin-producing neurons in the raphe nuclei (RN); this is referred to as the retino-raphe tract (see diagram below).
Figure 1. Effects of light on human circadian rhythms, sleep and mood, agosto 2019.
The more bright sunlight we’re exposed to, the more serotonin we produce. But the retino-raphe tract isn’t the only reason. Scientists have found that our skin produces serotonin when exposed to sunlight as well. Like our gut and brain, our skin produces serotonin for local use: serotonin helps to regulate the immune and vascular systems of the skin.
Researchers in Germany found that photostimulation (stimulation by light) of serotonin by the skin also increases levels of serotonin in the blood. Their study participants wore opaque goggles in order to eliminate photostimulation of serotonin through the retino-raphe tract. The study showed that just 15-20 minutes of UVA exposure resulted in increased levels of serotonin in the blood.
¿Es esta una de las razones por las que tomar el sol nos hace sentir bien? Bueno, los niveles saludables de serotonina en la sangre ayudan a regular muchas funciones fisiológicas, como se muestra en la Figura 2 anterior. Pero la serotonina no puede atravesar la barrera hematoencefálica; es por eso que la serotonina oral directa no se receta para la depresión. En cambio, los inhibidores selectivos de la recaptación de serotonina (ISRS) se utilizan para inhibir la reabsorción de serotonina por las neuronas en el cerebro, lo que aumenta los niveles de serotonina circulante y mejora el estado de ánimo.
However, rat experiments demonstrate how the serotonin transporter (SERT), which is present in the blood-brain barrier, may allow serotonin (5-HT) levels in the brain to affect levels in the body, and vice versa. The science of how this works is not completely understood yet. For now, if you want to increase your serotonin levels naturally, it’s probably best to address each area of synthesis—brain, skin, and gut—so that each area can produce the serotonin that it needs locally, and potentially all contribute to your overall health.
¿Qué sucede cuando los niveles de serotonina son bajos?
Since serotonin helps to regulate so many functions of our brain and body, lower than normal levels (serotonin deficiency) can cause or contribute to a wide range of symptoms. Higher than normal levels of serotonin are dangerous too; this is referred to as serotonin syndrome or toxicity, and it’s typically caused by taking medications that cause serotonin to build up in the body.
Los síntomas de la deficiencia de serotonina incluyen:
- Depresión estacional o crónica
- Ansiedad y preocupación
- Ataques de pánico
- Fobias, obsesiones y comportamiento compulsivo o impulsivo
- Baja autoestima
- Agresividad e irritabilidad
- Hiperactividad
- Insomnio y alteraciones del ciclo del sueño.
- Intestino irritable y malestar gastrointestinal
- PMS y disfunción hormonal
- Aumento de peso y antojos de carbohidratos
- Trastornos de la alimentación
- Fatiga
- Fibromialgia
- Dolor crónico y dolor muscular.
- Migrañas
- Mala memoria y deterioro cognitivo
- Abuso de alcohol
Serotonin helps to regulate virtually all aspects of human behavior, including mood, anger, aggression, reward, appetite, memory, perception, sexuality, attention, and more. This is why drugs targeting serotonergic activity and serotonin receptors in the central nervous system are prescribed or in development for the treatment of nearly every neuropsychiatric disorder.
Researchers have shown how bright light stimulates serotonin production through the retino-raphe tract, resulting in similar reduction of depressive behavior as SSRIs. They’ve also shown the reverse—that light deprivation produces depressive behavior. Serotonin production is one of the reasons why bright light therapy (BLT) is now used to treat seasonal and non-seasonal depression.
Depression, bipolar disorder, anxiety, and rates of completed suicide tend to increase during the winter months when people get less exposure to sunlight. Mood disorders are complex, but it’s clear that low serotonin levels play a role in these seasonal swings.
The relationship between neurotransmitters and mood is most often researched by examining how imbalanced levels of these chemicals affect mood. But researchers in Montreal did an interesting study to explore the opposite: how mood affects levels of serotonin. They asked study participants to recall memories in which they felt sad, happy, and neutral. Positron emission tomography (PET) scans showed that reported levels of happiness correlated with increased serotonin synthesis, and reported levels of sadness correlated with decreased serotonin synthesis. The participants’ self-induced moods directly affected their serotonin levels. This study suggests that the relationship between serotonin and mood may be two-way, with each affecting the other.
Of particular interest to the readers of this blog is how serotonin levels affect pain perception. Serotonin plays a fundamental role in pain perception in both the central and peripheral nervous systems. Serotonin regulates pain information sent from peripheral nerve fibers to the spinal cord and brain, and helps to modulate the psychological perception of pain in the cortical and limbic regions of the brain. This is why serotonergic drugs can be effective in managing chronic pain disorders. For example, women with Fibromialgia have significantly low serum serotonin levels, which helps to explain their heightened pain sensation, related symptoms such as gastrointestinal and sleep issues, and positive response to SSRIs.
¿Qué es la melatonina y cómo la producimos?
La melatonina es una hormona mejor conocida por regular nuestro ciclo de sueño-vigilia. También funciona como antioxidante y antiinflamatorio, y ayuda a regular la presión arterial y la función reproductiva.
Our brain produces melatonin in response to darkness—this is called “dim-light melatonin onset.” When our retinas detect darkness, a signal is sent through the retinohypothalamic tract to the suprachiasmatic nuclei, a brain region that controls circadian rhythms. From there, a signal is sent to the pineal gland, a small endocrine gland in our brain (see diagram of the retino-raphe tract above) that produces melatonin. This is why dimming the lights in your house and avoiding the blue light of televisions is recommended before going to bed: blue light suppresses melatonin synthesis. While melatonin doesn’t actually make us fall asleep, it plays the essential role of letting our brain know that it’s time to go to sleep.
La serotonina es un precursor de la melatonina; la glándula pineal usa serotonina para sintetizar melatonina. Cuanto más saludables sean nuestros niveles de serotonina, más probable es que también tengamos niveles saludables de melatonina.
When the pineal gland produces melatonin, it is then released into the bloodstream and distributed throughout the body. Research shows that melatonin reaches maximum levels between 2:00am and 4:00am in healthy individuals. As daylight approaches and our retinas detect increasing levels of light, melatonin levels fall. During the daytime, melatonin levels are low or undetectable.
In addition to the pineal gland, melatonin is produced throughout the body for local use. Photoreceptors of the retina produce melatonin to help protect the health and function of the eye. The gastrointestinal tract produces melatonin to regulate the health and function of the intestinal epithelium (gut lining), enhance the immune system of the gut, and relax the GI muscles. And melatonin produced by the skin protects against oxidative stress and ultraviolet radiation-induced damage to the skin.
¿Qué sucede cuando los niveles de melatonina son bajos?
As you would expect, melatonin deficiency or dysfunction is associated with circadian rhythm sleep disorders. These disorders typically involve difficulty falling asleep, frequent waking and inability to stay asleep, and waking up too early and not being able to fall back to sleep.
Low levels of melatonin play a role in stress and mood disorders as well. Low serotonin levels contribute to depressive symptoms and melatonin deficiency. The resulting lack of sleep contributes to increased levels of cortisol (a stress hormone) and depressive symptoms.
Melatonin secretion is altered in neurodegenerative conditions including Alzheimer’s disease and Parkinson’s disease. Production of the hormone also naturally decreases with age, and this decline in melatonin levels has been suggested to be one of the major causes of age-related neurodegeneration. In the central nervous system, melatonin regulates antioxidant and prooxidant enzymes, prevents damage caused by free radicals, promotes survival of neurons under increased oxidative stress, and prevents buildup and toxicity of amyloid plaques. Studies show that melatonin may slow progression of neurodegenerative diseases as well as improve sleep efficiency and cognitive function.
Melatonin deficiency weakens the immune system, making us more susceptible to viral and bacterial infections, autoimmune conditions, inflammation, and even cancer. Melatonin is an antioxidant and free radical scavenger, and plays an important role in our innate immune system, our first line of defense against attack. Melatonin can inhibit growth of cancerous tumors, and may help prevent breast cancer, prostate cancer, gastric cancer, and colorectal cancer. It also protects healthy cells from radiation-induced and chemotherapy-induced toxicity, so it can be used as an adjuvant of cancer therapies.
While we tend to be most aware of melatonin’s function in the brain—its effect on our sleep patterns—about 500 times more melatonin is produced in our gut than in our brain. As such, local melatonin deficiency may lead to health problems in the gastrointestinal tract. In the GI tract, melatonin acts as a free radical scavenger, reduces secretion of hydrochloric acid, stimulates the immune system, and increases microcirculation. It protects the mucosa (protective lining of the GI tract) against various irritants, and heals lesions including stomatitis, esophagitis, gastritis, and peptic ulcers. Because of its many benefits, researchers suggest that melatonin can be used for prevention or treatment of colorectal cancer, ulcerative colitis, gastric ulcers, irritable bowel syndrome, and childhood colic.
Cómo aumentar sus niveles de serotonina y melatonina de forma natural
If you want to improve your mood, regulate your pain perception, regulate your sleep cycle and improve your sleep quality, boosting your brain’s production of serotonin and melatonin should be at the top of your list. And by now you know the best way to do it—go outside!
Timing is important: Being exposed to natural light in the morning—without sunglasses—advances our circadian clock, stimulating melatonin production earlier in the evening and making it easier to fall asleep at night. Daylight exposure later in the day has not been shown to have the same positive effects on circadian rhythms. In addition to regulating our sleep-wake cycle, our circadian rhythms also regulate hormone production, appetite, core body temperature, brain wave activity, and cell regeneration. Keeping our circadian clock properly set is important for our overall health.
¿Cuánto tiempo debes pasar al aire libre? Bueno, considere que los humanos evolucionaron viviendo completamente al aire libre, por lo que los sistemas de nuestro cerebro y nuestro cuerpo están diseñados para funcionar mejor con mucha luz natural. Y hasta hace relativamente poco, gran parte de la población mundial se dedicaba a la agricultura y pasaba gran parte del día al aire libre. El cambio a la vida en interiores es reciente y es un gran contribuyente a las enfermedades crónicas. La mayoría de nosotros vivimos nuestra vida privados de la luz natural brillante que es esencial para nuestra salud. Por lo tanto, cuanto más, mejor, siempre y cuando tome las medidas necesarias para protegerse contra el cáncer de piel.
Since we’ve depleted the ozone layer, we’re exposed to more ultraviolet rays, increasing our risk of skin cancer. However, this does not mean you should avoid the sun completely—it’s all about moderation. Protect your skin and avoid long periods of time in direct sunlight, especially during midday when sunlight is most intense. And remember, you can sit in the shade while still exposing your eyes to daylight, which is critical for serotonin production.
Another way to boost serotonin levels is with exercise. Exercise increases levels of tryptophan (the precursor to serotonin) in the brain, and these elevated levels persist after exercise. Exercise also increases the firing rate of serotonin neurons, resulting in an increase in release and synthesis of serotonin.
Termine su día atenuando las luces de su casa por la noche antes de acostarse. Una vez que se acueste, evite mirar televisión o dispositivos móviles; su luz azul inhibirá la producción de melatonina. En su lugar, lea un libro o deje que una de las muchas meditaciones guiadas gratuitas en YouTube lo adormezca.
If you spend much of the day indoors, find ways to make getting outside part of your regular routine. Get in touch with your primal need for daylight and darkness and their effects on your biological rhythms. Your brain and body will thank you for it!
Lectura recomendada:
The Pain Relief Secret: How to Retrain Your Nervous System, Heal Your Body, and Overcome Chronic Pain by Sarah Warren, CSE
Somatics: Reawakening the Mind’s Control of Movement, Flexibility and Health by Thomas Hanna
