For decades, the sun has been presented almost exclusively as a risk. However, from a biological perspective, sunlight is a fundamental regulatory signal for the human body.
Life on Earth would not exist without the sun. And our body is not designed to live completely apart from it.
Vitamin D: more than a vitamin
Sun exposure is the main pathway for vitamin D synthesis in humans. When the skin receives UVB radiation, it triggers the production of vitamin D3, which is later converted into its active form in the body.
Vitamin D does not act only on the bones. It behaves as a regulatory hormone involved in multiple systems.
A review study published in The New England Journal of Medicine (Holick, 2007) indicated that vitamin D deficiency is associated with a higher risk of:
Cardiovascular disease
Autoimmune diseases
Infections
and some types of cancer
Holick MF. Vitamin D deficiency. N Engl J Med. 2007;357:266–281.
Likewise, a review in The Lancet Diabetes & Endocrinology (Autier et al., 2014) highlighted the widespread global prevalence of vitamin D insufficiency and its relationship with immune alterations.
Autier P et al. Vitamin D status and ill health. Lancet Diabetes Endocrinol. 2014;2(1):76–89.
Sunlight and mitochondrial function
Beyond vitamin D, natural light directly influences mitochondrial function.
Research in photobiomodulation has shown that certain wavelengths (especially red and near-infrared) can:
Increase ATP production
Reduce oxidative stress
Improve cellular repair
A study published in Seminars in Cell & Developmental Biology (Hamblin, 2016) describes how light acts on cytochrome c oxidase in the mitochondria, modulating cellular metabolism.
Hamblin MR. Mechanisms and applications of the anti-inflammatory effects of photobiomodulation. Semin Cell Dev Biol. 2016;56:73–82.
Although natural sunlight exposure is not identical to clinical light therapy, these studies support the idea that light is a relevant metabolic variable.
Sunscreen and vitamin D synthesis
High-SPF sunscreens are designed to block UVB radiation, precisely the type needed to synthesize vitamin D.
A study published in The American Journal of Clinical Nutrition (Matsuoka et al., 1987) showed that proper sunscreen use can significantly reduce the skin’s production of vitamin D.
Matsuoka LY et al. Sunscreens suppress cutaneous vitamin D3 synthesis. Am J Clin Nutr. 1987;46(5):1024–1027.
However, under real-life conditions, many people do not apply sunscreen in sufficient amounts to completely block synthesis.
Balance is key:
brief and conscious exposure without reaching skin redness, followed by appropriate protection during prolonged exposure.
Responsible exposure
Various experts in endocrinology and public health suggest that short and regular exposures may be sufficient to maintain adequate vitamin D levels.
The required time depends on:
Skin phototype
Latitude
Season
Time of day
In general, between 10 and 20 minutes of exposure during lower-intensity sunlight hours may be sufficient for many light-skinned individuals, without reaching skin damage.
The sun as a systemic regulator
In addition to vitamin D, natural light regulates:
Circadian rhythms (Czeisler et al., Science, 1999)
Melatonin production
Mood (linked to seasonal affective disorder)
Adequate exposure to daylight is associated with better sleep quality and hormonal regulation.
Note of responsibility
Sun exposure should be adapted to each individual. Personal history, dermatological background, and specific medical conditions require individual evaluation.
The goal is not to promote prolonged exposure without protection or to ignore the risks associated with excessive sun exposure. Rather, it is about restoring a conscious and balanced relationship with natural light, which is an essential part of the proper functioning of our organism.
This article does not aim to offer absolute truths, but to open a direction of inquiry. You are invited to do your own research, to stay informed, to contrast sources, and to explore which habits are most appropriate for you according to your context, your health, and your environment.
Personal experience
In my personal experience, more than ten years ago, a blood test revealed that I had a vitamin D deficiency. My doctor mentioned that they were encountering many similar cases, which was striking—especially considering that I was born in the Canary Islands, known for their abundant sunlight, and that I had spent years enjoying the outdoors. However, I had stopped exposing myself to the sun without protection.
From that moment, I began supplementing vitamin D under the guidance of specialists and, at the same time, incorporating short periods of sun exposure without sunscreen (20–30 minutes), mainly in the morning or late afternoon, avoiding peak intensity hours. Over time, I noticed significant changes in my overall well-being.
Each body is different. Listening, observing, and acting with awareness is part of holistic care.