Serotonin… your happy hormone!

It regulates mood, appetite, emotions, memory and learning, sleep, and digestion.

95% of our serotonin is produced by endocrine cells in the intestines (gut) and acts as a hormone. Gut serotonin helps control peristalsis (motility), pushing food in the right direction through the digestive tract. It also helps fluid secretion and the chemical breakdown of food.

Gut serotonin cannot cross the blood-brain barrier (BBB). So the central nervous system (brain) produces about 5% of our serotonin. To do this, your gut needs to breakdown protein you have eaten into amino acids (think of these as single proteins). From there, tryptophan (an amino acid) is converted by your gut bacteria into 5-htp. This metabolite can cross the BBB to create serotonin in the brain. Serotonin produced in the brain acts as a chemical communicator (neurotransmitter). It carries signals between nerve cells. Serotonin directly or indirectly affects around forty million brain cells. Pretty important huh?

How does sunshine come into the picture?

Sunlight directly affects how much serotonin you produce. This is known as the photostimulation of serotonin. For example, when sunlight enters your eyes, it stimulates a part of your retina (back of your eye), that signals your brain to produce serotonin. Serotonin is also found in cutaneous tissue, suggesting a skin serotonergic system. This means that serotonin is produced in your skin, in response to sunlight. (Think similarly to Vitamin D).

Do you need another excuse to get outside?

Serotonin levels are lowest in winter and brain serotonin turnover correlates significantly with the amount of bright sunlight. Do you ever feel weirdly down or unmotivated when it’s a dark, dismal day? There is a very fitting term for this; SAD – seasonal affective disorder. The winter blues, shorter days, more time spent indoors, and little exposure to natural sunlight. The Nordic countries see more intense depressive and anxious symptoms, and general lower moods between November and March.
Kind of SAD, hey?

So what can you do about this?

• My biggest tip is to get outside shortly after waking up. This will help regulate your sleep/wake cycle (your circadian rhythm). Try to expose both skin and eyes (yes, that means no shades first thing in the morning) to natural light for 10–15-minutes to stimulate serotonin production. This then helps your body produce melatonin later in the day. Melatonin helps induce sleepiness (more on this later).

• If you work indoors, it’s important to get outside.  Do you eat lunch at your desk? Do you stay in the shared kitchen, and only leave the office at home time? I promise you that popping out for 10-15 minutes during your lunch break (again, exposing eyes and skin to sunlight) will do you a world of good. Probably even keep you more focused for the rest of the afternoon. Why do you want to spend all day indoors anyway? Get outside, clock up some steps, and get back to your desk feeling refreshed. 

We could deep-dive into serotonin, melatonin, and Vitamin D… but for now, look up from your phone. Pop it in your pocket, and enjoy the view.

References:

1. Sunshine, Serotonin, and Skin
2. Serotonin in the gut
3. Benefits of Sunlight
4. Effect of sunlight and season on serotonin turnover in the brain