In life, some people are keen on sunbathing, whether it's sunbathing outdoors or at the beach, or simply enjoying the sunlight indoors daily; while others seem to rarely get sun exposure, covering up thoroughly for sun protection when going out, and drawing the curtains even when there is ample sunlight at home. So, what long-term effects does loving sun exposure versus never getting sun exposure have on the body?
Recently, a study published in the international journal Cell Metabolism made an unexpected discovery: humans might also need "photosynthesis"! Sunlight is not only a "regulator" of mood but also an invisible "operator" of the body's metabolism.
In December 2025, a study published in the international journal Cell Metabolism found that compared to artificial lighting, exposure to natural light (sunlight) during normal office hours can significantly improve the metabolic levels of patients with type 2 diabetes, leading to more stable blood sugar, increased fat utilization, and a better alignment of the human biological clock.
This study invited 13 patients with type 2 diabetes to participate. Each person worked for about 4 days in two different office environments: one with only artificial lighting, and the other filled with natural sunlight. The two experiments were separated by at least 4 weeks, with all other conditions such as diet, activity, and sleep kept completely identical. Therefore, any changes in metabolic status could only be attributed to the difference in light exposure.
The findings were surprising:
Blood sugar became more "obedient": Under natural light, the time patients spent within the target blood glucose range increased from 43.3% to 50.9%, equivalent to nearly 2 extra hours of stable blood sugar per day.
The body preferred "burning fat": In the natural light environment, the body was more willing to burn fat for energy instead of relying on carbohydrates, leading to a healthier metabolic pattern.
The biological clock was "calibrated": Evening melatonin secretion was more sufficient, sleep quality improved, and the metabolic rhythm became more harmonious.
Why can artificial light never replace sunlight?
1. Significant difference in light intensity: The illuminance outdoors on a sunny day can be as high as 100,000 lux, and even on an overcast day, it ranges from 1,000 to 10,000 lux. In contrast, the illumination from typical home lighting is only 100 to 500 lux, an intensity insufficient to be effective.
2. Difference in spectral completeness: Natural light is a continuous full-spectrum light source, containing all wavebands including ultraviolet, visible light, and infrared rays. It provides the body with complete spectral stimulation, helping to regulate physiological rhythms and promote vitamin D synthesis, among other benefits. For example, morning sunlight is rich in natural blue light, which can effectively inhibit melatonin secretion, sending a clear "it's daytime" signal to the body, thereby precisely calibrating the biological clock.
Artificial light, however, typically has a discontinuous spectrum and cannot simulate the full spectrum of natural light. Long-term use may affect the body's normal physiological response to light.
Get more sun exposure, and these 5 aspects of your body will improve imperceptibly.
Bones: Promotes vitamin D synthesis. Vitamin D plays a crucial role in protecting the skeletal system, regulating the immune system, protecting the cardiovascular system, and reducing inflammation levels. And getting sunlight is the primary way we obtain vitamin D. 90% of the vitamin D the human body needs is synthesized by the skin itself through ultraviolet exposure, with only 10% coming from food.
Mood: Improves emotions and mental health. Feeling happy when basking in the sun has a scientific basis. In 2021, a study involving over 400,000 people published in the international Journal of Affective Disorders found that lack of daylight exposure is a risk factor for depressive symptoms, low mood, and insomnia. Getting sufficient natural light daily improves a person's mood and sleep quality.
Brain: Helps improve brain cognition. In 2022, a study involving over 360,000 people with a 9-year follow-up, published in BMC Medicine, found that appropriate sun exposure helps prevent dementia. When outdoor sunlight exposure time is shorter, the risk of dementia increases significantly. Compared to people with an average daily outdoor light exposure of 1.5 hours, for every 0.5-hour reduction in outdoor light exposure time, the risk of dementia increased by 28.7%.
Lifespan: Contributes to extending healthspan. In 2016, a 20-year study of nearly 30,000 Swedish women published in the British Journal of Internal Medicine found that people who got the most sun exposure had a life expectancy 0.6 to 2.1 years longer than those who avoided the sun.
Cardiovascular: Endocrine health improves. Increased exposure to natural light enhances insulin sensitivity and lowers triglyceride levels, thereby helping to reduce the risk of type 2 diabetes and cardiovascular disease.
5 simple techniques to easily "capture" natural light in daily life:
Work or study near a window: Try to position your desk or study area close to a window. Even if you cannot get direct sunlight, the scattered natural light indoors is more metabolically friendly than artificial light sources.
Take an outdoor walk after lunch: After lunch, use 15 to 20 minutes to walk outside. This not only aids post-meal digestion and relieves drowsiness but also effectively "recharges" your midday natural light exposure.
Incorporate natural light during your commute: If you spend most of the day indoors, make full use of your commute time to get natural light exposure. Choose to walk or cycle to work, or get off one stop early to walk if time permits.
Create a sunny corner at home: When designing your home environment, choose light-colored walls and furniture to enhance indoor light reflection. If possible, set up a "sunny corner" in your home with ample natural light.
Schedule regular "light therapy": Every 1 to 2 hours, leave your work area and stand by a window or gaze into the distance for 5 minutes. This not only gives your eyes a rest but also allows your body to receive the rhythmic signals of natural light.
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