Go ahead, soak up some sun — it’s good for you

Sci­en­tist Michael F. Holick says our fear of can­cer is mak­ing us sick

The Washington Post Sunday - - OUTLOOK - mfholick@bu.edu Michael F. Holick is a pro­fes­sor of medicine, phys­i­ol­ogy and bio­physics at Bos­ton Univer­sity Med­i­cal Cen­ter.

For decades now, our sun has been re­viled and de­mo­nized. The mes­sage from the med­i­cal com­mu­nity: Avoid di­rect ex­po­sure, or face an in­creased risk of skin can­cer. As the Amer­i­can Can­cer So­ci­ety help­fully put it in one ad cam­paign: “Fry Now. Pay Later.” The Amer­i­can Academy of Der­ma­tol­ogy rec­om­mends never ex­pos­ing bare skin to the sun, or even a cloudy sky, with­out sun­screen. The Food and Drug Ad­min­is­tra­tion calls ul­tra­vi­o­let ra­di­a­tion a car­cino­gen. These mes­sages have caused wide­spread para­noia about sun­light, es­pe­cially among par­ents who re­li­giously ap­ply sun pro­tec­tion mul­ti­ple times a day on their chil­dren. Af­ter TV chef Nigella Law­son was pho­tographed cov­ered head to an­kle in a black “mod­esty” swim­suit at the beach, she ex­plained that she didn’t want to get burned.

But while we need to avoid can­cer, we also need vi­ta­min D, and the sun is the only re­li­able way to get it out­side of a daily sup­ple­ment. Aus­tralia’s decades-long public cam­paign to curb its skin can­cer rates and en­cour­age less sun ex­po­sure has been un­for­tu­nately ef­fec­tive: 31 per­cent of Aus­tralian adults are now vi­ta­min D de­fi­cient, which is linked with a num­ber of se­ri­ous and deadly con­di­tions, in­clud­ing sev­eral can­cers. Sun­screen dra­mat­i­cally lim­its the pro­duc­tion of vi­ta­min D— SPF 30 re­duces it by 97 per­cent. Mean­while, the risks as­so­ci­ated with sen­si­ble sun ex­po­sure have been ex­ag­ger­ated by well-mean­ing health author­i­ties, and the mea­sures to guard against them of­ten have noth­ing to do with the sun’s oc­ca­sion­ally ma­lig­nant ef­fects. Con­trary to the para­noia gen­er­ated by years of mes­sag­ing, the sun is not our en­emy. It’s safe to step back out­side — and, please, go easy on the sun­screen.

Vi­ta­min D has a num­ber of cru­cial func­tions. It’s ac­tu­ally a hor­mone, and its ac­tive form is re­spon­si­ble for reg­u­lat­ing the ab­sorp­tion of

di­etary cal­cium and phos­pho­rus, two nu­tri­ents es­sen­tial for bone health and neu­ro­mus­cu­lar ac­tiv­ity. Vi­ta­min D also reg­u­lates cel­lu­lar growth, keep­ing cells healthy and help­ing to pre­vent them from be­com­ing ma­lig­nant. A re­cent study found that adults who in­creased their vi­ta­min D in­take dur­ing the win­ter en­hanced 291 genes in their cir­cu­lat­ing im­mune cells. These genes con­trol more than 80 biologic pro­cesses, in­clud­ing help­ing cells re­pair their dam­aged DNA, pro­mot­ing the death of cells that are in the process of be­com­ing can­cer­ous and im­prov­ing im­mune func­tion to help fight in­fec­tions.

A lack of vi­ta­min D is as­so­ci­ated with in­creased risk for Type 1 and 2 di­a­betes, mul­ti­ple scle­ro­sis, rheuma­toid arthri­tis, Crohn’s dis­ease, car­dio­vas­cu­lar dis­ease, stroke, de­pres­sion, Alzheimer’s dis­ease, schizophre­nia, colon and breast can­cer, in­fluenza and tu­ber­cu­lo­sis. Vi­ta­min D de­fi­ciency is more likely to oc­cur at higher lat­i­tudes and in the win­ter, when the an­gle of the sun is more oblique; in the 1940s, doc­tors found that liv­ing at higher lat­i­tudes in­creased the risk of dy­ing of can­cer. Of the 30 lead­ing causes of deaths in the United States in 2010, 19 were linked to low vi­ta­min D sta­tus.

Vi­ta­min D de­fi­ciency in preg­nant women has been as­so­ci­ated with a higher risk of preeclamp­sia, which can cause fa­tal com­pli­ca­tions. Women lack­ing the vi­ta­min are three times more likely to re­quire a Cae­sarean sec­tion com­pared with women who are vi­ta­min D suf­fi­cient at the time they give birth. Poor birth out­comes have also been as­so­ci­ated with in-utero vi­ta­min D de­fi­ciency, and those in­fants and young chil­dren are more likely to de­velop wheez­ing dis­or­ders.

Con­versely, ex­po­sure to more sun, and the sub­se­quent in­creased vi­ta­min D, is good for you. Liv­ing be­low a lat­i­tude sim­i­lar to that of Los An­ge­les and At­lanta for the first 10 years of life re­duces the risk of de­vel­op­ing mul­ti­ple scle­ro­sis by more than 50 per­cent, and those who were born and live near the equa­tor are 15 times less likely to de­velop Type 1 di­a­betes com­pared with peo­ple liv­ing in more north­ern or south­ern lat­i­tudes. A study in Canada re­vealed that women who had the most sun ex­po­sure as teenagers and young adults re­duced their chance of de­vel­op­ing breast can­cer later in life by al­most 70 per­cent.

We sim­ply aren’t get­ting enough vi­ta­min D. The USDA’s 2015 Di­etary Guide­lines Ad­vi­sory Com­mit­tee placed the com­pound high on its list of un­der con­sumed nu­tri­ents; it also iden­ti­fied vi­ta­min D de­fi­ciency as a public health threat. There are few di­etary sources for vi­ta­min D. For­ti­fied foods in­clud­ing milk, or­ange juice, mar­garine and ce­re­als have small amounts; oily fish, cod liver oil and sun-dried mush­rooms have some, but you can’t sub­sist on those. This means we must rely on the sun, just as our hunter-gatherer an­ces­tors did.

When we are ex­posed to sun­light, more than 200 dif­fer­ent pack­ets of energy en­ter our skin. The pho­tons with the low­est wave­lengths, ul­tra­vi­o­let B (UVB) ra­di­a­tion, have the most energy and are ef­fi­ciently ab­sorbed in the up­per layer of the skin by DNA, RNA and pro­teins as well as many small mol­e­cules, in­clud­ing 7-de­hy­dro­c­holes­terol, which is even­tu­ally con­verted to vi­ta­min D. UVB stim­u­lates the pro­duc­tion of melanin, a nat­u­ral sun­screen that pro­tects the skin from the dam­ag­ing ef­fects of ex­ces­sive sun ex­po­sure, and beta en­dor­phin, which helps cre­ate the “run­ner’s high” and a feel­ing of well-be­ing.

Ul­tra­vi­o­let A (UVA) ra­di­a­tion has less energy. These pho­tons are not ef­fi­ciently ab­sorbed in the epi­der­mis and pen­e­trate more deeply, ini­ti­at­ing the pro­duc­tion of ni­tric ox­ide. The ni­tric ox­ide causes smooth mus­cle re­lax­ation, lead­ing to a widen­ing of blood ves­sels and lower blood pres­sure. It im­proves cir­cu­la­tion in the skin, thereby en­hanc­ing wound heal­ing, es­pe­cially in pa­tients with di­a­betes. It also causes gas­troin­testi­nal smooth mus­cle re­lax­ation and is in­volved in learn­ing and mem­ory. UVA ra­di­a­tion causes im­mune sup­pres­sion, de­creas­ing in­flam­ma­tory skin con­di­tions and al­ler­gic asthma.

It would be wrong and foolish, of course, to say that sun ex­po­sure isn’t dan­ger­ous. Just as sun­light trig­gers the cru­cial pro­duc­tion of vi­ta­min D, it also sets in mo­tion neg­a­tive pro­cesses. Ex­ces­sive ex­po­sure to the sun dam­ages DNA in skin cells, which in turn can cause non­melanoma skin can­cer. So­lar UVA ra­di­a­tion pro­duces free rad­i­cal oxy­gen, a po­tent ox­i­dant, in the skin, lead­ing to wrin­kles and dam­age; it also de­presses im­mune re­ac­tions that nor­mally de­stroy de­vel­op­ing skin tu­mors, re­sult­ing in in­creased risk for skin can­cer. Ad­di­tion­ally, this sup­pres­sion can de­crease re­sis­tance to some in­fec­tious dis­eases of the skin and lower im­mune re­sponse to some vac­cines. More than 3.5 mil­lion skin can­cers are di­ag­nosed in more than 2 mil­lion peo­ple in the United States an­nu­ally. An es­ti­mated 1 in 5 Amer­i­cans will de­velop skin can­cer in their life­times. This is not in­signif­i­cant.

Faced with high can­cer rates, health author­i­ties have rushed to damn the sun with­out tak­ing into ac­count the many sci­en­tif­i­cally doc­u­mented health ben­e­fits it pro­vides. Along the way, the dan­ger of sun ex­po­sure has been ex­ag­ger­ated. Melanomas cause more than 9,000 deaths each year, but they ac­count for only 5 per­cent of skin can­cer. What’s more, most melanomas oc­cur on the least sun-ex­posed parts of the body, such as the but­tock, the up­per arms and the back of the legs. Peo­ple who work out­doors ac­tu­ally have lower in­ci­dences of melanoma, de­spite spend­ing sig­nif­i­cantly more time in the sun than of­fice work­ers.

So how do we get sun re­spon­si­bly, bal­anc­ing the ben­e­fits against the risks? It’s com­pli­cated. The time of day, sea­son, lat­i­tude and de­gree of skin pig­men­ta­tion all in­flu­ence how much vi­ta­min D is pro­duced in the skin. The In­sti­tute of Medicine rec­om­mends that chil­dren over the age of 1 and adults up to 70 should re­ceive 600 units daily of vi­ta­min D; for ref­er­ence, re­search shows that an adult in a bathing suit who is ex­posed to the sun long enough to pro­duce a light pink­ness of the skin 24 hours later has got­ten the equiv­a­lent of 15,000 IUs. I sug­gest to my pa­tients that they go out in the sun be­tween 10 a.m. and 3 p.m. (very lit­tle if any vi­ta­m­inD is pro­duced out­side those hours) for half the time it would take them to de­velop a mild sun­burn — while cov­er­ing the face and hands with sun­screen but leav­ing other parts of the body ex­posed. Af­ter this ex­po­sure, I urge them to use sun pro­tec­tion to pre­vent burn­ing.

The rec­om­men­da­tion to avoid sun­light is based on the premise that this re­duces the risk of skin can­cer, in­clud­ing the most deadly form, melanoma. Yet ab­sti­nence hasn’t worked: Skin can­cer rates con­tinue to in­crease un­abated, and vi­ta­min D de­fi­ciency — and the many ills as­so­ci­ated with it — is ris­ing. Health-care or­ga­ni­za­tions need to rec­og­nize, as the World Health Or­ga­ni­za­tion does, that small amounts of UV are ben­e­fi­cial and es­sen­tial to the pro­duc­tion of vi­ta­min D. The sun, used sen­si­bly, is not to be feared.


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