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.
Conclusion
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.
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