Part 13: Sunlight and human health

The relationship between sunlight and human health has long been scientifically studied.
Sunlight has various effects on our bodies, and among these, the relationship with substances such as vitamin D, melatonin, and serotonin has received particular attention.
This column explains how sunlight and these substances affect human health.

Vitamin D and sunlight

In recent years, as health awareness has increased, the relationship between vitamin D and sunlight has been attracting attention.
Vitamin D is an important nutrient essential to our health, and sunlight plays an essential role in its production.
Vitamin D plays an essential role in helping absorb calcium and phosphorus.
This not only maintains bone health, but also contributes to the normal functioning of the immune system and cell growth.
Vitamin D is also being studied for a wide range of health benefits, including prevention of cardiovascular disease and cancer, and anti-inflammatory effects.

The primary source of vitamin D is skin exposure to ultraviolet B (UVB) radiation from sunlight.
When UVB light hits the skin, cholesterol changes into the precursor 7-dehydrocholesterol, which is converted to vitamin D in the body.
Therefore, exposure to adequate amounts of sunlight is an essential element for vitamin D production.

・Vitamin D deficiency and countermeasures

In recent years, vitamin D deficiency has become a problem due to people spending more time indoors and taking thorough measures against UV rays to avoid sunburn.
Vitamin D deficiency can lead to health problems such as osteoporosis and weakened immune system.

Vitamin D can also be obtained from food.
Good food sources of vitamin D include fatty fish (salmon and tuna), egg yolks, and mushrooms.
Vitamin D supplements may also be considered, but it is important to seek professional advice.

However, excessive exposure to UV rays over a long period of time can have a negative effect on skin health.
It is important to avoid sunburns that are so intense that your skin turns red, and to expose yourself to adequate amounts of UV rays at appropriate times.
Especially in the summer, there is a risk of heatstroke and sunburn, so be careful not to expose yourself to too much sunlight.

・Melatonin and sleep rhythm

Good sleep is an essential element for living a healthy life.
In order to improve the quality of your sleep, it is important to understand the role of the hormone melatonin.
Melatonin is a hormone that plays a role in regulating the body's internal clock and day/night rhythm.

The human body clock is tuned to the natural solar cycle.
Melatonin is mainly produced in the hypothalamus of the optic nervous system, and its secretion amount is adjusted under the influence of sunlight.
In the morning, it becomes brighter, melatonin secretion decreases, and the body shifts to a state of wakefulness.
At night, when it gets dark, melatonin secretion increases and induces sleep.
This rhythm is also called the "circulatory rhythm", and the proper functioning of the body's internal clock supports healthy sleep.

How to balance melatonin

・Light management

Exposure to sufficient light during the day resets the body's internal clock.
On the other hand, it is important to avoid excessive brightness and refrain from using electronic devices at night.

・Regular lifestyle habits In order to adjust your sleep rhythm, it is important to go to bed and wake up at the same time every day.
Irregular lifestyle habits can disrupt your body's internal clock and affect melatonin secretion.

・Sleeping in a dark environment

Avoiding bright light before bed supports proper melatonin secretion.
Sleeping in a dark environment promotes quality sleep.

・Regular exercise

Exercise helps regulate your body clock and improves the quality of your sleep.
However, you need to be careful about strenuous exercise before going to bed, as it may have the opposite effect.

Melatonin is an important hormone that supports sleep quality and is closely related to your body clock.
Achieve healthy sleep while maintaining the balance of melatonin through appropriate brightness management and lifestyle changes.
Good quality sleep is directly connected to physical and mental health, and is the foundation for a fulfilling life.

Serotonin and mental health

Mental health is an important factor that has a significant impact on your sense of well-being and quality of life.
Among them, serotonin is also called the "happiness hormone", and its proper balance plays an important role in mental health.

Serotonin is one of the neurotransmitters controlled by the central nervous system.
This chemical affects a variety of physiological processes, including emotions, mood, sleep, appetite, and sexual desire.
When serotonin is present at appropriate levels, the following psychological effects are observed:

・Feeling happy and stable
Increased serotonin promotes feelings of well-being and positive mood.
Conversely, a lack of serotonin can increase symptoms of depression and anxiety.

・Resistance to stress

The presence of serotonin has the effect of increasing resistance to stress.
It is believed that when an appropriate serotonin balance is maintained, it becomes easier to deal with stress.

・Sleep adjustment

Serotonin also influences sleep regulation.
Serotonin is converted to melatonin at night, which maintains a normal sleep rhythm.

How to support your mental health

・Balanced diet

Serotonin is produced from the amino acid tryptophan.
Eating foods rich in tryptophan (bananas, nuts, fish, dairy products, etc.) can support serotonin production.

・Motion

Exercise has the effect of promoting the secretion of serotonin.
Moderate exercise makes you feel good and helps reduce stress.

・Use of sunlight

Exposure to sunlight stimulates the production of serotonin in the body.
We recommend going outside and soaking up natural light at appropriate times.

・Stress management

Stress causes an imbalance in serotonin.
Incorporate relaxation techniques and mindfulness to reduce stress and support stable serotonin levels.

Serotonin is a neurotransmitter that is deeply involved in mental health, influencing a sense of well-being and mental stability.
It is important to maintain appropriate levels of serotonin through a balanced diet, exercise, and stress management.
To support your mental health, understand the role of serotonin and take proactive care of it.

The role of sunlight in a healthy life

Sunbathing is one way to have a positive effect on your health, but the right method and timing are important.
Exposure to direct sunlight for long periods of time can lead to overexposure to UV rays, so appropriate time and UV protection are necessary.
Exposure to sunlight in the morning promotes vitamin D synthesis and melatonin reset.

Vitamin D, melatonin, and serotonin are interconnected to support healthy living.
Exposure to the right amount of sunlight helps balance these substances, improving bone health, sleep quality, and mental health.
Additionally, in today's society where we spend more and more time indoors, it is important to consciously go outside and let in some sunlight.






Written by: BARREL Editorial Department
Supervised by: Yuki Oe (Lecturer, Department of Lifestyle Design, Faculty of Human Culture, University of Shiga Prefecture)
Lecturer at the University of Shiga Prefecture, Faculty of Human Culture (Department of Lifestyle Design).
She specializes in architectural environments, light environments, lighting environments, and color environments.
She is a member of the Architectural Institute of Japan/Illumination Institute of Japan.
After completing her doctoral course at Nara Women's University Graduate School of Humanities, she worked in technology planning at Sharp.
She worked as an assistant professor in the Faculty of Science and Technology at Tokyo University of Science and as a part-time lecturer at Osaka Jonan Women's Junior College before reaching her current position.