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Why is sunlight important for our well-being (and for preventing cancer)?

Published by Connealy, MD on June 6, 2024

Why is sunlight important for our well-being (and for preventing cancer)?

Full-spectrum sunlight is essential for human health. Sunlight is energy. When it touches our cells, a cascade of effects take place, influencing our entire body. 

This topic is nuanced because we are often told to stay out of the sun. However, the human body is more complex than black-and-white statements. Research suggests that what we are told to avoid might be exactly what we need the most, especially given the high rates of vitamin D deficiency these days

The Benefits of Sunlight:

Humans evolved under the sun. We spent the majority of ancient history outside, with regular exposure to its light. Our bodies are designed to receive the sun’s inputs. In the early 2000s, scientists discovered that skin cells contain photoreceptors called opsins to detect sunlight and regulate our circadian rhythms. Before, opsins were believed to be only present in the eyes.

When opsins in the skin absorb light, they send signals to active proteins. These proteins stimulate physical responses such as the activation of enzymes, hormones, and neurotransmitters, which in turn, regulate wound healing, vitamin D production, gene expression, immune cell function, etc.

Many people today avoid the sun due to concerns about skin damage and cancer. However, this topic is nuanced. 

  • Avoiding sunlight can actually increase your cancer risk—stay tuned for the upcoming slides to discover possible reasons why. Studies indicate that maintaining adequate vitamin D levels, which we primarily obtain. from sun exposure, is crucial in lowering cancer risk.
  • It’s important to note that skin cancer is often linked to severe burns rather than regular sun exposure and is highly treatable, unlike many other forms of cancer.
  • Regular sun exposure (without burning) has been associated with a significant reduction of disease, increased metabolism, healthy hormone production, immune function, sleep cycles, etc.

Insufficient Sun Exposure Has Become a Real Public Health Problem: “Studies in the past decade indicate that insufficient sun exposure may be responsible for 340,000 deaths in the United States and 480,000 deaths in Europe per year, and an increased incidence of breast cancer, colorectal cancer, hypertension, cardiovascular disease, metabolic syndrome, multiple sclerosis, Alzheimer’s disease, autism, asthma, type 1 diabetes and myopia.” (PMID: 32668607).

Sunlight and Vitamin D:

Sunlight is essential for the production of vitamin D, which is synthesized when UVB rays come into contact with the skin. Vitamin D regulates immune function, cell growth and differentiation, mood and cognitive function, calcium absorption, bone health, insulin sensitivity, and cardiovascular health. 

It is essential that we get enough vitamin D so that our cells can properly function. Vitamin D produced from the sun is used more efficiently by the body, however, supplementation is sometimes necessary.  

It’s estimated that a significant portion of the population, about 42% of adults in the US, is deficient in vitamin D. This deficiency is a major health concern, and many patients at the clinic are found to be deficient.

Low vitamin D is a major risk factor for cancer, cardiovascular disease, and other chronic conditions.

Beyond vitamin D production, sunlight is essential for:

  • A healthy circadian rhythm: Sunlight exposure influences our sleep and waking cycles, cortisol production, metabolism, and insulin levels.
  • Energy production: Sunlight exposure can enhance mitochondrial function, aiding in the efficient production of cellular energy, which is essential for overall vitality and health.
  • Hormone balance: Sunlight is essential for proper secretion of thyroid hormones, cortisol, and sex hormones like testosterone. 
  • Immune function: Exposure directly affects immune cells in the skin, contributing to a well-balanced immune response against infections and diseases.

A note on the solar spectrum:

Much of the light from the sun consists of infrared or near-infrared wavelengths. These wavelengths can penetrate deep into our skin and cells, where they stimulate various cellular processes. For example, red and near-infrared light can enhance mitochondrial function, increase cellular energy production (ATP), promote tissue repair and regeneration, and reduce inflammation. However, both ultraviolet and infrared exposure have important physiologic effects.

Tips for Sun Exposure: 

  • Avoid burning (use non-toxic sunblock, wear hats, rest in the shade, etc.)
  • Expose skin and eyes (without glasses or contacts) to natural light within an hour after waking up
  • Build a ‘sun callus’ by getting adequate exposure during the spring months so the body is less likely to burn in the summer
  • Build tolerance slowly
  • Eat a nutrient dense diet 
  • Spend time outside during sunrises and when IR exposure is highest 
  • Avoid excessive artificial blue light exposure

Tips for Choosing a Sunscreen: 

When purchasing sunscreen, I look for:

  • Micronized zinc oxide: This offers non-toxic SPF protection (needs to be at least 20%).
  • Low in titanium dioxide: Titanium dioxide usually causes a white cast.
  • Low in PUFAs: I avoid sunflower seed oil, almond oil, grapeseed oil, etc. These oils oxidize when exposed to heat and light and can cause cell damage.
  • No benzenes: Many sunscreens contain benzenes which are known carcinogens.
  • No fragrance: Fragrance has been linked to adverse reactions and usually contains undisclosed synthetic ingredients (up to 3,500 chemicals can be labeled as “fragrance” or “parfum”). 
  • Reef-safe (zinc oxide is safe)

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