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Dr. Sears' Blog

Keep Up with the Latest Nutrition Science
Written By: Dr. Barry Sears Creator of the Zone Diet

Written by Barry Sears
on August 07, 2016

We're told not using sunscreen causes cancer. Is this true, or a ploy to sell sunscreen? Dr. Sears shares perspectives on sunshine, Vitamin D and nitrates.

As the weather heats up, we continually hear the refrain that without using large amounts of sunscreen, we will get cancer and our lives will be shortened.  However, is that a true statement?  There is significant confusion about sun exposure and the benefits of sunscreens to block solar radiation.

Vitamin D, the Sunshine Vitamin

We are told that we need sunshine to make Vitamin D, which is true.  Once the sunscreen frenzy took off several decades ago, the end result was that Vitamin D levels decreased.  When people started testing routinely for Vitamin D, low Vitamin D levels seemed to be highly correlated with virtually every disease known to man.  Rather than reducing the use of sunscreens, the obvious answer was simply to take more Vitamin D as a supplement.  That simple logic dramatically increased the sales of Vitamin D.  However, correlation is not the same as causality.  In the last few years, numerous clinical trials have demonstrated that increasing Vitamin D levels in the blood by supplementation didn’t show any clinical benefit.  It appears that low levels of Vitamin D were simply a marker of poor health in general.

Yet at the same time, it was known that greater sun exposure decreased mortality instead of increasing it.  So if increasing Vitamin D wasn’t the answer, then what was?

Is Vitamin D as Beneficial as we Think? 

It turns out the answer may be nitric oxide.  The 1998 Nobel Prize in Medicine was awarded for understanding how nitric oxide improves vascular blood flow.  Although nitric oxide is a gas, it is also a hormone.  As a gas, it doesn’t need any receptor on the cell surface to enter into the interior of the cell as I pointed out in my book, The Anti-Aging Zone.  Great news, but unfortunately it is hard to store a gas like nitric oxide for future use.  So the body converts incoming sources of nitrogen (like amino acids or botanical compounds containing nitrogen) into nitrates that can be concentrated in the skin.  When exposed to sunshine, these stored nitrates in the skin are converted into nitric oxide that quickly spreads through the body to improve vascular flow rates.  This makes every organ in the body healthier because of better oxygen transfer because of increased vascular flow.

Obesity and Other Conditions May Suppress the Benefits of Sun

The plot gets even more interesting as chronic conditions such as obesity, metabolic syndrome (pre-diabetes), and diabetes suppress the sunlight-induced increase in nitric oxide.  So the combination of increased use of sunscreens (to block solar radiation) coupled with the increase in obesity, metabolic syndrome, and diabetes (that attenuate the making of Vitamin D) make it more difficult to maintain normal vascular blood flow.  The end result is that you are not very healthy.

Is it the Nitric Oxide or the Vitamin D?

Studies have shown that when mice fed a high-fat diet to make them obese are exposed to solar radiation they reduced their body fat, whereas obese mice taking high doses of Vitamin D with no sun exposure did not lose any fat.

This is also true at the opposite end of spectrum in elite athletes.  If you feed trained cyclists nitrates to increase their blood levels, then expose them to solar radiation prior to time trial in the lab, their performance is increased compared to running the same experiment without exposure to solar radiation prior to the time trial in the lab.

Do the Risks Outweigh the Benefits?

Although sun exposure remains a risk factor for skin cancer, the mortality from non-melanoma skin cancer is extremely low.  Actually intermittent sun exposure is a larger risk factor for the far more dangerous melanoma skin cancer.  However, chronic sun exposure and outdoor occupations may actually be protective in terms of reductions in both cardiovascular mortality and all-cause mortality.

So rather than sitting indoors all day, consuming Vitamin D supplements, and then slathering your body with sunscreens, try to get 20 minutes of sun exposure every day.  Beyond that time period, then wear sensible sun protection clothing during the rest of the day if you remain in the sun.  You will probably live longer in the process.

Related: Your Sunscreen May Actually Be DangerousNew call-to-actionReferences:

  1. Yang L et al. “Ultraviolet exposure and mortality among women in Sweden.  Cancer Epidemiol Biomarkers Prev 20:683-690 (2011).
  2. Berwik M. “Can UV exposure decrease mortality?’ Cancer Epidemiolo Biomarkers Prev 20:582-584 (2011).
  3. Linquvist PG et al. “Avoidance of sun exposure is a risk factor for all-cause mortality.” J Intern Med 276:77-86 (2014).
  4. Mowbray M et al. “Enzyme-independent NO stores in human skin.”  J Invest Dermatol 129:834-842 (2009).
  5. Geldenhuys S et al. “Ultraviolet radiation suppresses obesity and symptoms of metabolic syndrome independently of vitamin D in mice fed a high-fat diet.”  Diabetes 63:3759-3769 (2014).

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