The literature is replete with the adverse health effects of incorrect sun exposure, and I don't dispute them. These include sunburn and increased risk of skin cancer and eye diseases. However, summer is in full swing, and I love the additional sunlight it brings in the northern hemisphere. I crave sun exposure and feel much better when I can get it regularly. Some people have noticed that I am very tan (at least for me) and warned me that I might be jeopardizing my health. My skin type allows me to spend up to two hours in the sun, which is not enough for me to burn, even though I don't use sunscreen. I want to explain why the risks are exaggerated and why it is essential to get regular non-burning sun exposure.

Disclaimer

I am going to cite studies in this post as usual. Observational and demographic studies are ranked on the bottom when it comes to reliable conclusions. Compounding the confusion as to which factors are relevant when looking at human health is that we tend to reduce complicated biological systems into a few simple mechanisms when trying to communicate to the average person without any scientific backgrounds. Take the subject of sun exposure. Most folks believe that UV light helps us make vitamin D, which is mainly responsible for any benefits associated with sunlight exposure. Conversely, UV is considered mostly harmful, cancer-causing, and to be generally avoided. I want to broaden the subject while keeping this post as simple as possible. Just remember, as you are reading this, that correlation does not mean causation, and we still have more work to do to understand the subject of sun exposure and human health.

Our Ancestors Were Forced to Remain In the Sun For Long Periods or Perish

We could not have survived as a species without the innate ability to be in the sun for long periods. All of our food sources are outside. Whether you believe in evolution or not, both the evolutionists and creationists tell the same story. The garden of Eden was not a farm. God made it contain everything we need to sustain ourselves outside AFTER he made the sun. Do you think he goofed? I think not. Similarly, hunting and gathering are done in the great outdoors, not in huts and caves.

Not Enough Sun Is Bad

Inadequate sun exposure results in increased risks of all-cause mortality (meaning the total of EVERYTHING that will kill you), colorectal cancer, breast cancer, non-Hodgkin's lymphoma, prostate cancer, pancreatic cancer, hypertension, cardiovascular disease, metabolic syndrome, type 2 diabetes, obesity, Alzheimer disease, multiple sclerosis, type 1 diabetes, rheumatoid arthritis, psoriasis, non-alcoholic fatty liver disease, statin intolerance, macular degeneration, and myopia. Vitamin D gets all of the credit for the health benefits associated with sun exposure. How true is this?

Production of vitamin D occurs when we expose ourselves to sunlight strong enough to contain UVB rays. The benefits are numerous. I have written about it in a previous post, so click here if you need a refresher. However, a 2016 paper found that the decrease in these conditions was independent of vitamin D status, demonstrating that sun exposure does more than increase vitamin D. (1) A comprehensive analysis concluded that supplementation with vitamin D did not affect weight loss, coronary artery disease or hypertension, or reducing signs of cardiometabolic risk such as glucose tolerance, insulin sensitivity or circulating lipids. (2) The conclusion taken from this is that other factors are at play besides vitamin D, so it may only serve as a marker.

A Swedish Study: More Sun Equals Longer Life Expectancy (WTF?)

A 2016 study concluded that women with the most sun exposure during their lives lived longer, even though they had more cancer. They concluded that they had more cancer because they were living longer lives. They explained that the sun exposure produced less cardiovascular disease, and the result extended lives. Furthermore, they included data on smoking and concluded that sun-exposed women who smoked survived longer. They ranked sun avoidance as a similar risk to smoking! (3) The vitamin D theory does not lend support to their conclusion. 

Another 2016 paper proposed several mechanisms for reducing cardiovascular disease associated with the ultraviolet component of sunlight. 

• Heme-Oxygenase levels increase with sun exposure. The mechanism is a bit complex to get into in this post. In a nutshell, it reduces body weight, blood glucose levels, and total cholesterol levels, all implicated in cardiovascular mortality.

• Systemic inflammation has a long association with many degenerative diseases, especially heart disease. UV exposure has systemic anti-inflammatory effects, which are known to reduce heart disease. UV exposure is a catalyst promoting the suppressive activity of specialized cells critical to proper control of inflammation. They are regulatory T cells, myeloid cells, and other immune cells. 

•  Obesity is closely associated with cardiovascular disease. Seasonal changes in weight are normal. We should expect to weigh more in the colder, darker months. Exposure of mice to ultraviolet A radiation increased serum levels of α-MSH, which helps prevent obesity by suppressing appetite and promoting energy consumption. Researchers propose that humans share the same mechanism. 

Sunlight And Nitric Oxide: The Best Explanation For Sunlight's Cardiovascular Benefits

Nitric oxide is well known to decrease blood pressure, which is the single most crucial risk factor for heart disease. Whole-body irradiation of healthy adult volunteers to UVA radiation reduced blood pressure in healthy young adult males, and it lasted for 30 min. UV induced nitric oxide can have benefits for the control of the cardiometabolic dysfunction associated with obesity. (6)

Blood Pressure Regulation Requires Healthy Oral Plaque

The bacteria in the mouth are known to be crucial for nitric oxide production and provide a new therapeutic target for high blood pressure management. The presence or absence of select and specific bacteria help to maintain blood pressure levels. Removal of oral bacteria through antiseptic mouthwash or overuse of antibiotics causes blood pressure to increase. Allowing recolonization of nitrate- and nitrite-reducing bacteria can normalize blood pressure. Management of high blood pressure through oral microbiome maintenance may become a crucial step in heart disease treatments. (5)

Summary

• Many studies about health are observational, demographic, rely on questionnaires, and are of the lowest quality. We should be cautious about concluding any causation from them.

• Our bodies produce vitamin D through UV exposure.

• Adequate vitamin D is needed to maintain health.

• Vitamin D supplementation is not as beneficial as we would like to believe.

• Sun exposure upregulates many mechanisms.

• These mechanisms all help to explain the benefits of sun exposure.

• UV exposure upregulates nitric oxide.

• Nitric oxide lowers blood pressure.

• Lower blood pressure reduces heart disease.

• Heart disease is associated with much of human mortality.

• Observational demographic correlates higher sun exposure to living longer, even though it is associated with more cancer.

Before venturing out in the sun, you might want to check out this post. It includes further information about sun exposure, skin types, and more. Not surprisingly, I am attending a pool party today and I am really looking forward to it.