If you have noticed something shift in your body and mood this week, you are not imagining it. As of today, the clocks have fallen back an hour. The sun will set before 5 p.m. across most of the country. And while we tend to frame this as a minor inconvenience, a scheduling adjustment, or a welcome extra hour of sleep, what is actually happening inside the body is considerably more profound. The light is changing, and your brain is responding in ways that ripple through your energy, your sleep, your appetite, and your emotional life.
The central player in this seasonal story is serotonin, a neurotransmitter that most people associate with happiness but that does far more than regulate mood. Understanding what serotonin actually does, and what happens to it as daylight diminishes, can help you work with your biology rather than against it during the months ahead.
What Serotonin Is Really Doing
Serotonin is often described as the brain's feel-good chemical, but that framing undersells it considerably. It is a neurotransmitter and hormone that regulates a remarkable range of physiological functions: sleep architecture, appetite, digestion, cognitive performance, pain perception, and emotional regulation. Roughly 90 percent of the body's serotonin is produced not in the brain but in the gut, which helps explain why gut health and emotional wellbeing are so closely linked. The 10 percent that lives in the central nervous system, however, is the portion that governs mood, motivation, and our overall sense of calm. What most people do not know is that serotonin is also a direct precursor to melatonin, the hormone that regulates sleep. As darkness increases, the pineal gland converts serotonin into melatonin. This means that the availability of serotonin in the system directly influences the quality and timing of sleep. When serotonin levels are lower, the conversion to melatonin is disrupted, which is one reason why so many people experience irregular sleep patterns as the seasons turn.
The Light-Serotonin Connection
The relationship between sunlight and serotonin is not metaphorical. It is biochemical. Light enters the retina and triggers the release of serotonin in the brain through pathways in the raphe nuclei, the cluster of neurons in the brainstem responsible for serotonin production. When light exposure decreases, so does the signaling that drives serotonin synthesis.
A landmark study published in the Archives of General Psychiatry by researchers at the University of Toronto and the Medical University of Vienna measured serotonin transporter binding in the brains of 88 healthy volunteers using PET imaging over several years. They found that transporter binding was significantly higher in the darker months of fall and winter than in spring and summer. The significance of this is counterintuitive: higher transporter binding means that serotonin is being cleared from the synaptic space more rapidly, effectively lowering the amount of serotonin available to the brain. In other words, the shorter the day, the faster the brain pulls serotonin away from the circuits that depend on it.
This mechanism, which the researchers described as previously undescribed in physiologic literature, provides a biological basis for the seasonal mood and energy shifts that millions of people report each autumn and winter. Seasonal Affective Disorder, the clinical form of this phenomenon, affects an estimated 10 million Americans. But a much larger portion of the population experiences what researchers call subsyndromal seasonal changes: lower energy, increased carbohydrate cravings, a pull toward withdrawal, and a general heaviness that does not quite rise to the level of a diagnosis but that is nonetheless real and disruptive.
Why the Body Craves More Than Rest
The seasonal serotonin dip triggers a cascade of compensatory behaviors that many people recognize but rarely trace back to their source. The craving for bread, pasta, and sweets in the fall is not weakness or habit. Carbohydrates promote the absorption of tryptophan, the amino acid precursor to serotonin, across the blood-brain barrier. The body is, in a very real sense, trying to self-medicate.
Similarly, the impulse to slow down, to hibernate, to spend evenings on the couch rather than out in the world, is partly a physiological response to the melatonin shift. As serotonin converts to melatonin earlier in the evening, the body signals rest sooner. For some people this aligns beautifully with a need for seasonal restoration. For others, it collides with the demands of a life that does not slow down in November, which is where the tension lives.
How to Support Your Serotonin
There is no single remedy for the seasonal serotonin shift, but there are meaningful interventions that the research supports. Morning light exposure, ideally within the first hour of waking, is consistently the most effective behavioral tool. Even on overcast days, outdoor light exposure registers at far higher lux levels than most indoor environments, and the retinal signals it sends are what the brain needs to maintain serotonin production. A 20-minute walk before 9 a.m. is worth more than most supplements.
Physical movement is another well-documented lever. Exercise raises serotonin synthesis and increases its availability at the synapse. The mechanism here involves the reduced competition between serotonin precursors and branched-chain amino acids for transport into the brain, a competition that exercise shifts in serotonin's favor. And then there is touch. A body of research led by Dr. Tiffany Field at the University of Miami Touch Research Institute has demonstrated that therapeutic touch, specifically massage, stimulates the vagus nerve in ways that promote serotonin release and lower cortisol, the stress hormone that competes directly with serotonin's calming influence. Multiple studies from the Institute have shown that regular massage reduces markers of stress, anxiety, and depression, and that these effects are measurable at the biochemical level. Touch is not a luxury in the physiological sense. It is a mechanism.
The Role of Reflexology
Reflexology, which applies precise pressure to specific zones on the feet that correspond to organ systems throughout the body, is a particularly well-suited practice for the seasonal transition. The feet contain some of the highest concentrations of nerve endings in the body, and the stimulation of those nerves during a reflexology session activates the parasympathetic nervous system, the branch responsible for rest, digestion, and recovery. When the parasympathetic system is engaged, cortisol drops, the vagus nerve is stimulated, and the conditions for serotonin activity are restored.
At BAO FOOT SPA, our Signature Reflexology treatments are designed to deliver exactly this kind of systemic reset. A session begins with a warm foot soak, moves through carefully applied pressure across the full reflexology map of the foot, and finishes with work on the lower leg and calf to support circulation and lymphatic movement. Many clients report a quality of settled calm after a session that is difficult to find through other means, and what they are describing is the nervous system finding a lower baseline, which is precisely what the serotonin-depleted body needs most in the fall.
Our Body Massage services, which include Swedish, deep tissue, and our restorative BAO Signature Massage, offer the broader therapeutic touch that the research connects to serotonin and cortisol regulation. For those looking to build a consistent practice through the winter months, we offer memberships at both our Santa Monica and Beverly Hills locations that make regular sessions genuinely accessible.
Work With the Season, Not Against It
The goal is not to override the seasonal shift. The body is doing something ancient and intelligent when it responds to shorter days by slowing down, conserving energy, and pulling inward. The goal is to give it what it needs to navigate that shift without the collateral costs: the flattened mood, the disrupted sleep, the low-grade depletion that accumulates across the darker months.
Morning light. Daily movement. Nourishing food. Deliberate rest. And regular, intentional touch. These are not indulgences. They are the inputs your nervous system is asking for, even when it cannot name what it needs.
SOURCES
Praschak-Rieder, N., et al. (2008). Seasonal variation in human brain serotonin transporter binding. Archives of General Psychiatry, 65(9), 1072-1078. Field, T. (2002). Massage therapy. Monitor on Psychology, American Psychological Association. Field, T. (2014). Touch (2nd ed.). MIT Press. Young, S. N. (2007). How to increase serotonin in the human brain without drugs. Journal of Psychiatry and Neuroscience, 32(6), 394-399. American Academy of Family Physicians. Seasonal Affective Disorder. familydoctor.org.
