[Home] [Therapies]





Laurance Johnston, Ph.D.

As discussed before, sunlight is healthy in moderation. In fact, studies suggest that we are much more likely to die from disorders aggravated by chronic underexposure to sunlight than ailments aggravated by overexposure. The bottom line is that sunlight is healthy in moderation.

Vitamin D

Much, but not all, of the sun’s health benefits are due to sunlight catalyzing the production of vitamin D in the skin. This nutrient is critically important for us, its lack being implicated in the development of numerous disorders, including osteoporosis, cancer, cardiovascular disease, multiple sclerosis, and diabetes.

Unfortunately, because we are often cloistered in offices and lather on sunscreen when outside, many of us are vitamin-D deficient and don’t know it. Even dermatologists, the sun-avoidance advocates, now recognize vitamin D’s vital health role; however, rather than easing up on a dogmatically held conviction to shun the sun at all cost, they encourage patients to take vitamin-D supplements.

Although such supplementation is a generally meritorious suggestion, it is lacking in several respects: First, many of us have no idea that we may be vitamin-D deficient, a problem just a little routine sun exposure can nip in the bud. Second, not all of sunlight’s health benefits are mediated through vitamin-D, several examples of which are summarized below.

Non-Vitamin-D Benefits

First, evidence indicates that sunlight is good for your heart because it reduces blood pressure.  In general, blood pressure is lower in summertime and increases the further you live from the more sun-intense equator. Even small reductions in blood pressure can substantially lessen deaths due to heart disease, stroke and other disorders.

In addition to vitamin D, sunlight stimulates the synthesis of nitric oxide in the skin (not the laughing gas nitrous oxide). Composed of one molecule each of oxygen and nitrogen, nitric oxide (NO) is called a free radical because it has an unpaired electron, making it highly reactive and short-lived. In spite of NO’s instability, scientists have shown that it plays important biological roles, regulating and affecting many physiological processes.

Briefly, sunlight is composed of electromagnetic radiation of varying wavelengths, ranging from the long-wavelength infrared light to the short-wavelength ultraviolet (UV) light. The UV light is further subdivided into UVA and even shorter wavelength UVB components. While UVB radiation initiates vitamin-D production in the skin, the UVA component triggers NO synthesis.

UVA light penetrates fairly deeply into the skin, where it causes the photodecomposition of various nitrogen-containing compounds, generating NO. In turn, this NO diffuses into the skin’s deeper, capillary-containing layers where it enters into the systemic blood circulation. Once in circulation, the NO interacts with the inner lining of the blood vessels (endothelium) where it signals the smooth muscle surrounding the vessels to relax, dilating the vessels, increasing blood flow, and lowering blood pressure. By being precursors to NO, long-used heart medications nitroglycerine and amyl nitrite work through this vasodilation mechanism.

Dr. Christian Opländer and colleagues (Germany) have studied this process in subjects exposed to UVA light at a dose equivalent to the UVA amount received after 45 minutes of sun exposure in a temperate climate zone (Circulation Research, 2010). The subjects were compared to controls who wore UV-impermeable clothing.  The results indicated that UVA light resulted in a rapid and significant lowering of blood pressure (both the systolic and diastolic components). The effects persisted for some time and were correlated with the UVA-induced production of NO by the skin.

Endorphin Rush

Mood elevation is another sun-exposure benefit that cannot be duplicated by merely consuming a vitamin-D pill. As a personal anecdote, after a long, depressing overcast winter in the Pacific Northwest, I drove across the nearby, cloud-hugging Cascade Mountains, descending onto their sun-soaked eastern slopes, where I spent all afternoon sunbathing at hot springs. It was a real high for me, displacing the malaise generated from months of gloomy weather.

Although not conclusively demonstrated, studies suggest that this mood-enhancing benefit may be mediated by the sun’s ability to stimulate the synthesis of endorphins in the skin. Associated with the so-called “runner’s high” or “endorphin rush” of strenuous exercise, endorphins are feel-good, neurotransmitter molecules produced by the body, which are similar in structure to opioid drugs. It is theorized that the sun-induced endorphins created in the skin diffuse into the blood where they can reach the brain in sufficient concentrations to enhance mood.

One study supporting this theory was carried out by Dr. Mandeep Kaur and associates at Wake Forest University (NC) (J Am Acad Dermatol, 2006). Their results indicated that the tanning-associated high experienced by frequent tanners was prevented when they were given naltrexone - a drug commonly used to treat addiction due to its ability to block the euphoric effects of opioid-like molecules. The results suggested that sunlight-induced mood enhancement is probably mediated through opioid-like molecules, the most likely candidate being the endorphins.


We have evolved over the eons to be in the sun. Sun avoidance does not resonate with who we are physiologically, and will have adverse health consequences over the long term. Although vitamin-D supplementation compensates to some degree for the lack of sun exposure, sunlight has other benefits that are not mediated through this nutrient. There is a middle ground. You don’t have to fry yourself in the sun, but you can, indeed, get some sun exposure confident that the health benefits will outweigh detriments.