7 Health Truths About Sunlight Exposure
You may have been told that the sun’s ultraviolet (UV) rays are dangerous and can contribute to premature skin aging and a significant increase in your chance of developing skin cancer.
You may have also heard catchy slogans such as the 5 s’s of sun safety (slip on a t-shirt, slop on some sunblock, slap on a hat, slide on the sunglasses, and shade yourself frequently) that position the sun as an enemy that we must protect ourselves against. With skin cancer rates on the rise, it seems logical to protect yourself against the looming threat of DNA damage and wrinkly skin.
But what if avoiding the sun may be more dangerous to your health in terms of developing other types of chronic diseases?
Current research regarding sun exposure has shifted to examine the importance of sun exposure in maintaining good health, creating a need for a new definition of sun safety that optimizes the health benefits of sun exposure while minimizing the drawbacks. We’re now well aware of the importance of sun exposure in combating vitamin D deficiency. Additionally, research is beginning to explore the numerous health benefits of soaking up the sun’s rays that may not have anything to do with vitamin D.
The Skin Cancer Scare Revisited
The most convincing argument for avoiding excessive sun exposure is the direct correlation between UV exposure and the development of skin cancer.
There’s no doubt that overexposure to UV rays in the form of a sunburn greatly increases your chances of developing skin cancer.
Although it may be true that skin cancer is one of the most common types of cancer, with rates increasing yearly by 1.9%, the statistics are sometimes misleading, since there isn’t always a distinction made between non-melanoma carcinomas and melanoma.1
Non-melanoma carcinomas include basal cell carcinoma (BCC) and squamous cell carcinoma (SCC). BCC is the most common skin cancer and is rarely fatal because it doesn’t usually metastasize, meaning it doesn’t spread to other areas of the body and is usually removed and treated successfully. SCC is the second most common form of skin cancer, and although it’s more aggressive than BCC, it also rarely metastasizes.2 According to the Skin Cancer Foundation, only 2% of SCC cases were fatal.3
Cutaneous malignant melanoma (CMM) accounts for the majority of the reported fatal cases of skin cancer. However, this type of cancer only accounts for 2% of skin cancer cases. Furthermore, the Skin Cancer Foundation reports that the average survival of diagnosed melanoma cases has increased from 49% in the 1950s to about 91% today. In addition, the survival rate increases to 98% if the CMM is detected before metastasis involving the lymph nodes and distant organs occurs.3
As mentioned previously, overexposure to UV rays that results in a sunburn greatly increases your chances of developing these types of cancer. But as you’ll find out later, regular sun exposure may actually defend against sunburn and your chances of developing CMM, the most fatal form of skin cancer.
Why Sun is Essential
Despite increasing rates of skin cancer, there’s mounting evidence that sun exposure shouldn’t be avoided.
Humans have evolved in nature, with constant and sometimes unremitting exposure to sunlight. As a result, our circadian rhythms governing our metabolism, endocrine function, and sleep and wake cycles are intimately related to the cycles of the sun and consequently our health.
At some point in human evolution, natural selection favored hairlessness, yielding a predominantly naked human race and increased skin exposure to sunlight. It’s proposed that with this adaptation also came the selection of skin types with higher concentrations of melanin, otherwise known as skin pigment, as there was no longer fur to limit the penetrating UV rays.
It’s theorized that the depigmentation in human skin characteristic of Caucasians occurred approximately 60,000 years ago as we migrated from Africa to higher latitudes with less direct sunlight.4
It turns out that this was a crucial adaptation, preserving the efficiency of vitamin D3 production that’s catalyzed by penetrating UVB rays. Vitamin D3, which can be more accurately classified as a hormone, is utilized by nearly every cell in the human body and is involved in bone health, immune function, and modulating gene expression (among other regulatory processes).
As Sayer Ji, founder of GreenMedinfo.com points out, the selection for skin types with lower melanin concentrations points to the importance of vitamin D3 for our survival. Sayer Ji includes over 40 articles pointing to the therapeutic effects of vitamin D3 and sunlight exposure on his website, adding to the body of evidence that humans need the sun to thrive.
The following true facts will help to provide a more complete picture of the health benefits of sun exposure and why, to functional medical practitioners like Chris Kresser, natural sunlight exposure is not optional.
Truth #1: Sun Exposure Optimizes Vitamin D Levels
In Chris Kresser’s book The Paleo Cure, he explains that 17 types of cancer, as well as heart disease, stroke, hypertension, autoimmunity, type 1 and 2 diabetes, depression, increased risk of infection, and birth defects have all been correlated with vitamin D deficiency. Taking this into consideration, it seems necessary to consider how humans naturally obtain vitamin D.
Dr. Mark Hyman, MD, reports that at least 80% of the vitamin D utilized by our body must come from the sun.5
When skin is exposed to the UVB rays in the sun, a chemical called 7-dehydrocholesterol is converted to previtamin D3 in the epidermal and dermal cells of your skin and is then hydroxylated to form active 1,25-dihydroxyvitamin D3. This form of vitamin D exerts its effects by attaching to vitamin D receptor (VDR) sites on nearly every cell in the body.
While it’s tempting to rely on supplementation to achieve adequate levels of vitamin D3, Sayer Ji reminds us that it’s probably the synthesis of vitamin D3 in concert with other metabolic processes powered by the sun that contribute to its true therapeutic effects.
Some literature reviews on the efficacy of vitamin D supplementation show that it isn’t entirely effective in treating the diseases that are correlated to a deficiency in vitamin D.6,7,8 This observation may support the idea that the actions of vitamin D3 should be considered in the context of its synthesis from the sun.
According to Chris Kresser, it may also take high doses of vitamin D3 that are well over the recommended daily intake to optimize levels. Kresser also points out that the optimal dosage will vary from person to person and can depend on intestinal health, dietary fat intake, and VDR expression, among other factors.
Vitamin D3 levels and how well the body functions as a result may also be related to levels of circulating calcium, vitamin K2, and vitamin A.9 Although the risk of vitamin D3 toxicity is low, it’s a fat-soluble vitamin; if it’s found in excess, it’s retained in fat cells in the body. Conversely, it’s impossible for your body to overdose on vitamin D3 or to cause downstream nutritional imbalances when you get it directly from sun exposure.
Truth #2: Sun Exposure May Decrease Cancer Risk
Although decreasing UV exposure has been shown to decrease skin cancer risk, many studies have shown that lack of sun exposure may have a longer list of health implications. There have been multiple studies that correlate increasing geographical latitude to an increased incidence of most cancers.10,11,12
Since increasing latitude correlates to a decrease in direct sunlight, it would follow that the decrease in direct sunlight might correlate to an increased risk of cancer.
One literature review on the topic reported that higher latitudes increased the chances of dying of lymphoma, breast, colon, ovarian, pancreatic, and prostate cancer. This review also cited a study that showed doubling the recommended daily intake of vitamin D3 and calcium reduced the predicted incidence of developing all types of cancer evaluated by at least half in a specific group of women.12
Dr. Mark Hyman, MD, is a functional medicine practitioner who emphasizes the anti-cancer actions of vitamin D3 from sun exposure. He points out that vitamin D3 regulates the uncontrolled cell growth characteristic of cancer cells and simultaneously improves the cells’ ability to differentiate into non-cancerous cells.5
This could explain why more than one study comments on the fact that although an increased number of intermittent intense UV exposures increases the likelihood of developing CMM, there’s a protective effect of regular sun exposure by activation of the vitamin D3 pathway.11,12
Along the same lines, one study shows that indoor workers have a higher chance of developing CMM than outdoor works.13 The authors of this study attribute the discrepancy to the fact that UVA, which is able to pass through the glass windows of the indoor work environment, breaks down the vitamin D3 levels in the skin. Secondly, they propose that regular sun exposure maintains a high level of vitamin D3, which is able to mitigate UV damage to DNA, reducing the risk of a developing a fatal skin cancer.
Truth #3: Sun Exposure Defends Against Autoimmunity
The sun’s impact on autoimmune diseases adds to the potential downsides of staying out of the sun.
Studies have shown that limiting sun exposure may also exacerbate autoimmune conditions such as multiple sclerosis (MS), type 1 diabetes, psoriasis, rheumatoid arthritis, and possibly others.12,14
The sun’s UV rays can be immunosuppressive, providing a possible mechanism for the development of skin cancer. However, in cases of autoimmunity, the immune system’s overactivity is what underlies symptoms, and so the sun may prevent the onset and improve prognosis of these types of diseases.
It’s been shown that there’s a direct correlation between increasing latitude and the prevalence of MS, as well as type 1 diabetes. Although vitamin D3 is credited with having immunomodulatory effects, UVA and UVB rays can also directly suppress the action of autoimmune T-cells by upregulating specific T-regulatory cells.12
Another study reports that sunlight is able to disrupt inflammatory cytokine signaling and suppress autoimmune T-cells.14 Both studies comment on the sun-induced release of alpha melanocyte-stimulating hormone (α-MSH) by the color-producing skin cells and its anti-inflammatory and immune-regulating effect on the skin and body.
Truth #4: Sun Exposure is Beneficial for Cardiovascular Health
Sun exposure has been shown to be protective against heart attack, stroke, and the development of heart disease.
Chris Kresser, LAc, MS, attributes this protective effect to the increase in nitric oxide that results from sun exposure. Nitric oxide causes blood vessels to relax, consequently reducing blood pressure. This may be one explanation for why sun exposure decreases your risk of heart attack, heart disease, and stroke.
Kresser cites more than one study that examines the correlation between sun exposure and cardiovascular health in his book The Paleo Cure. Kresser summarizes one study that isolated UV light exposure as the only variable in an experiment set up to achieve a significant decrease in blood pressure.
A latitude correlational study (similar to the studies finding a correlation between increasing latitude and prevalence for cancers and autoimmune disorders) was also included and showed the same direct correlation between increasing latitude/less direct sunlight and an increase in the prevalence of hypertension. Kresser also includes a study from the UK that examined risk of death from heart disease with respect to latitude that found the same direct correlation. This correlation was still strong even when the authors of the study corrected for both risk and protective factors.
Not surprisingly, multiple studies cited in The Paleo Cure show the connection between vitamin D deficiency and the odds of heart disease and other heart disease-related mortality.
Truth #5: Sunlight is Important in Maintaining Healthy Circadian Rhythms
Much of the chemical signaling that takes place in our body is governed by a circadian rhythm.
A circadian rhythm is simply a characteristic pattern of change in particles in our bodies that repeats in a similar fashion with every 24-hour cycle of the sun.
For example, the production of cortisol, the stress hormone, and melatonin, the sleep hormone, both follow circadian rhythms that are inverse of one another.
The relative amounts and intensity of sunlight affects pineal gland activity and thus melatonin production. Melatonin has multiple different regulatory actions, including mitigating free radicals, modulating the immune system, and regulating endocrine activity.15 Melatonin suppresses the production of cortisol, and cortisol suppresses the production of melatonin in a negative feedback loop, regulating both daytime wakefulness and nighttime sleepiness.
One study examined the effect of appropriate daylight exposure and found an associated increase in cognition in the early evening and an easier time getting to sleep.16
Since chemicals that follow circadian rhythms are inherently dependent on the cycle of the sun, it’s obvious that lack of daytime sun exposure can interfere with the delicate dance between daytime and nighttime chemicals.
Lack of sun exposure from working indoors may affect your ability to stay awake during the day and consequently interfere with the production of melatonin at night.
To add insult to injury, artificial light exposures after sunset further delay the production of melatonin, contributing to difficulty sleeping and insomnia. Since quality sleep is important for maintaining overall health, you can see why optimizing sun exposure may be a good idea.
One review of circadian rhythm literature reports that about 10% of our genes have circadian rhythms. Interestingly, these circadian-dependent genes are predominantly the genes that maintain DNA integrity, programmed cell death, cell cycling, and differentiation processes that are important in preventing cancer.17
Truth #6: Sunlight is Important for Proper Brain Function
Sunlight can influence the brain in many different ways, including by regulating mood, lowering stress, optimizing cognition, and defending against neurodegenerative disorders such as Parkinson’s and Alzheimer’s.
Sunlight is important in maintaining adequate levels of mood-boosting chemicals such as serotonin and dopamine. Both serotonergic and dopaminergic pathways can be affected by sun exposure.18
Seasonal Affective Disorder (SAD) is the onset of depression with seasonal variations in sunlight, particularly in places at higher latitudes with significantly decreased amounts of sun exposure in the winter months. There’s evidence to suggest that the increased likelihood of depression from lack of sunlight is also accompanied by a decrease in cognitive function.19
A hospital study assessed the effect of light on the wellbeing of patients recovering from surgery and found that patients who were in rooms with the most direct sunlight were much better off than patients with less light. The study found that patients exposed to more daylight in their rooms reported lower stress and pain levels. Interestingly, the patients in the brighter rooms needed significantly less pain medication.20
Sunlight and vitamin D3 production seem to be neuroprotective.21
Vitamin D3 is involved in the regulation of the central nervous system, which would explain why some studies have found a correlation between vitamin D3 deficiency and Parkinson’s disease.22
Vitamin D3 has also been shown to induce the breakdown of the amyloid plaques involved in Alzheimer’s disease.23
One study examined vitamin D3 intake over the course of 7 years and found that the group with the highest intake of vitamin D3 had a decreased risk of developing Alzheimer’s disease.24
Truth #7: Our Bodies Have Natural Sun-Blocking Abilities
It’s obvious that the sun offers a fair amount of advantages to human health. It isn’t surprising, then, that humans have evolved defense mechanisms that are able to mitigate the damaging effects of UVR exposure while maximizing the benefits.
Aside from the protective effect of vitamin D3 synthesis, a few other factors contribute to our to UVR stress resiliency.
One of these factors is the production of melanin. Melanin, not to be confused with the sleep hormone melatonin, is the pigment produced from specialized cells in the skin called melanocytes. The melanin concentration of your skin determines the color of your skin, from white to black and everything in between. Melanocytes produce melanin and redistribute it in the top layer of your skin in response to UVR-induced DNA damage and free radical formation.
According to Sayer Ji, melanin is able convert UVR directly into heat, preventing even more DNA damage with more UVR exposure.25 This might explain why regular, less intense exposures to UVR could be protective against CMM, since this type of exposure builds melanin and minimizes burns. It follows that melanin content also reduces the production of vitamin D3, since there’s less UVB penetrating the skin.
Antioxidant levels are also important in combating oxidative stress, even when it isn’t specific to UVR exposure.
Since free radical formation is a hallmark of UVA exposure, it’s important to consider antioxidants in the diet as well as the production of glutathione, the body’s main endogenous (produced inside the body) antioxidant.
It’s been shown that dietary intake of antioxidants has a protective effect against sunburn and skin cancer.26,27,28
Melatonin, which we previously discussed in this list, also has antioxidant capabilities in response to UVR damage to the skin.15
Becoming Sun Smart
Hopefully you’ve gained some useful insights on the necessity of sun exposure and why you can’t (or shouldn’t) avoid it despite the threat of skin cancer.
So what’s the optimal dose of sunlight?
How can we reap the benefits of sunlight and simultaneously protect ourselves from the damage of UV rays?
The optimal amount of sun exposure will be different for different people. The darker your skin, the more melanin you have, and the more exposure you need to produce sufficient vitamin D3. For lighter-skinned people who generally burn easily and don’t develop tans easily, less exposure is required.
You want to aim to have enough exposure to induce the activation of melanocytes and D3 synthesis but to simultaneously avoid burning. It might take you a few tries to achieve this delicate balance.
In situations where you can’t control the amount of sun you’re exposed to, the use of sunscreen might be necessary to avoid burning, especially for people with lighter skin.
This also holds true if you’re taking medications such as antibiotics, anti-histamines, and others used in the treatment of skin conditions, cancer, diabetes, and heart disease.
It’s important to choose sunscreens that are the least toxic and have broad spectrum UV protection. However, as mentioned previously, antioxidants have proved to be efficient internal sun blockers, mitigating the effects of sun-induced DNA damage and oxidative stress. So if you’re going to be spending significant amounts of time in the sun, it might be a good idea to load up on antioxidant-dense foods. This is probably always a good idea, rain or shine.
Along these lines, Sayer Ji summarizes an interesting new study that shows chlorophyll, the substance that enables photosynthesis and gives veggies their deep green color, may actually be utilized by our cells in a process that’s similar to photosynthesis.29 This is contrary to the belief that only plants are able to convert the energy from the sun into usable energy. This study is just one example in a myriad of emerging studies shedding light on the untapped potential of the sun’s energy that may far outshine its drawbacks.