Dear Mark: Sun Exposure and Glass

These days many of us go to work in the dark and leave greeted by the same. Those lucky enough to have windows next to their desks or work stations might think, “Hey, at least I get some sun exposure during the day.” But how does sun exposure through glass compare with direct sunlight? One reader brought up the topic this week.

Dear Mark,

I work in an office and have a big picture window in front of my desk. Don’t get me wrong – I love the light and all, but my friend told me you don’t get any real sunlight benefits (vitamin D, etc.) through glass. Is that right? I’m guessing a tan is out as well. What’s the story on what gets through and what doesn’t? Love the site by the way.

Thanks to reader Rob for this week’s question. Sorry to rain on anyone’s parade here, but the friend is right and then some. Window light just isn’t the same as direct exposure – on many fronts. I think a view to the outside – particularly to a natural space – has its own benefits, but don’t count on healthy sun exposure being one of them.

Let’s talk UV rays, particularly UVA and UVB.

UVB rays are the triggers for vitamin D production in our bodies. Obviously, we need this. UVB rays penetrate the epidermis, the upper layers of our skin. UVA rays, on the other hand, penetrate more deeply into the basal section of the dermis, which is where most skin cancer develops. Excessive UVA exposure also associated with wrinkling, immune suppression, oxidative stress, and related aging.

When we’re outside in direct sunlight, our bodies absorb both rays. Although we’re exposed to the more damaging UVA rays, research shows that our concurrent exposure to UVB – and the subsequent vitamin D production – actually serves to counteract skin damage and inflammation.

When we’re sitting in front of a window, however, the exposure is different. Glass blocks the shorter-wave UVB rays while allowing most of the longer UVA rays to pass through. In short, we’re receiving the more damaging rays without the normal protective benefit of vitamin D production. This information might cause the corner window office lose a bit of its luster in your mind, but it’s important to keep the various risk factors in perspective here. Excessive UVA exposure is indeed a skin cancer risk factor, but this risk factor typically presents in the form of sunburn episodes in the first 18 years of life. Insufficient vitamin D levels, poor immune function, poor diet, insufficient sleep and overly stressful lifestyle habits are of far more concern than the UVA rays hitting your corner office or window of your delivery truck. In fact, most cases of melanoma are found in areas of the body that receive little or no sun exposure, in people who receive minimal sun exposure, and in people with insufficient vitamin D levels.

My philosophical disagreement with the medical community and Conventional Wisdom is often over an alarmist approach to health concerns. This mentality is often fueled by the media, where scare tactics and lowest common denominator sound bites deliver bigger ratings. Those standing to make a profit also fuel the hysteria, as we have seen with the dermatological and “skinceutical” communities promoting a blanket policy of avoiding (or lathering up against) the sun – to the great detriment of society.

In my next book Reconnect (working title), I’ll deliver an extensive chapter on the vitamin D/sun exposure/skin cancer risk, complete with detailed guidelines for how to maintain optimal vitamin D levels with absolutely no increased risk of cancer. For now, I’ll assert that living Primally, including obtaining a reasonable amount of exposure to direct sunlight to maintain a slight tan (and never burning), will dramatically reduce your risk of all forms of cancer and debilitating health problems common in modern life.

Regarding the windows of the offices, cars, autos, buses, trains and homes that we live with daily, I think enjoying the light (albeit filtered), stimulating view (hopefully!), and expanded perspective provide significant psychological health benefits (imagine commuting, working, or being at home all day without any window to the outside world!) that outweigh any material health concerns about skin damage from UVA exposure. That said, if you have a bunch of accumulated risk factors, such as being extremely fair skinned, living in the lower half of the continental US, with work space or work conditions that blast you with bright sunlight through glass during the peak sun intensity hours of 10am-3pm every day, you may want to consider using a “full spectrum” sunscreen that blocks both UVA and UVB rays during those summer months when UVA radiation is particularly strong. The term “full spectrum” indicates that the product blocks both UVA and UVB rays. This is the only type of sunscreen that you should ever use, since “regular” sunscreen blocks only UVB rays (preventing sunburn) but can often promote excessive UVA exposure by allowing you to stay outside longer than you ordinarily would without the deterrent of potential sunburn. Check out the Skin Cancer Foundation’s chart on sunblock ingredients and their UV properties.

You can also consider using tinted window films specially designed to block UVA rays. Although you’ll still get something like 80% of the visible light coming in, more than 99% of UVA rays won’t make it through. This might be especially prudent to use in a car window where infants or young children might be hit with lots of sunlight, since youngsters are especially vulnerable to skin damage from excessive sunlight.

The most important take-away on the topic is to be sure that you obtain enough vitamin D – from direct sunlight exposure and your diet. And of course load up on antioxidants to promote optimal immune function and cancer protection. As I’ll detail further in Reconnect (coming June 2011), it’s not difficult for most people to get enough sunlight to ensure healthy vitamin D levels, but in the colder months a vitamin D supplement can help ensure your levels are up to snuff.

Thanks for reading today. Be sure to share your thoughts and questions in the comment boards. Have a great week, everyone!

TAGS:  dear mark

About the Author

Mark Sisson is the founder of Mark’s Daily Apple, godfather to the Primal food and lifestyle movement, and the New York Times bestselling author of The Keto Reset Diet. His latest book is Keto for Life, where he discusses how he combines the keto diet with a Primal lifestyle for optimal health and longevity. Mark is the author of numerous other books as well, including The Primal Blueprint, which was credited with turbocharging the growth of the primal/paleo movement back in 2009. After spending three decades researching and educating folks on why food is the key component to achieving and maintaining optimal wellness, Mark launched Primal Kitchen, a real-food company that creates Primal/paleo, keto, and Whole30-friendly kitchen staples.

If you'd like to add an avatar to all of your comments click here!

48 thoughts on “Dear Mark: Sun Exposure and Glass”

Leave a Reply

Your email address will not be published. Required fields are marked *

  1. I’m fortunate to have a window that’s 5′ tall and 14′ wide on one wall of my ofice. No D, but I can’t imagine how depressing it would be inhere without the natural light. When I worked in secure buildings while working in the defense industry, I never saw saw the sun. Just flourescent light. It really does get on your nerves after 12 hours of that kind of light. Flourescent light actaully flashes at a frequency higher than can be detected by the eye, but I think that high frequency flashing has a detrimental effect. I know it can trigger seizures in the seizure prone.

    1. There is an overlap between the flickering and what people can see. I can see some flourescent lights flicker, and it’s highly disturbing.

  2. A vitamin D supplement during the colder months will also strengthen your immune system immensely. Look for 5000 IU in the daily dosage. The best way your body can absorb an oral vitamin d supplement is a spray for under your tongue.

  3. Hello Mark,

    I’m new to your forum and just ordered your book online. I’m so looking forward to reading it! I’ve already read a ton on MDA and I hope this is just the kick in the head I needed to keep me on track to a better healthier lifestyle. So far I’m inspired and motivated! My question is indeed regarding sun exposure, I am quite fair skinned and freckled. I know how important vitamin D is, especially obtaining it from sun exposure. Unfortunately, I sunburn easily, especially out west, and the sunscreen I use is usually 45SPF and above and I usually slather it on religiously if I know I’m going to be exposed for any length of time. What is the minimum amount of exposure for the skin to absorb vitamin D without getting sunburned? If I don’t have sunscreen on and depending on what location I’m in, I’m burnt within 5 min (AZ, CO) to 15 minutes(IL). I see most sunscreens block out all UVA and UVB rays(most consider this one to be the main cause of skin cancers which contradicts what’s in the article). How can us fair skinned people get the benefit of sunkissed vitamin D without the added risk of sunburnt skin and eventual skin cancers?

    1. I too used to burn in 5 – 15 mins and am also fair-skinned and freckled. However, since eating Primally I now burn much less quickly and can be out in the sunshine for around 30 mins without sunscreen with no ill-effects. Be interesting to see if you have a similar experience, lots of readers seem to report improved sun tolerance once they eat Primally.

      Mark did have a post a while back with a link to a site that could calulate exposure time and Vit D manufacture according to latitude, skin type etc. Should be searchable in the box top right.

      1. The fact that diet can effect the rate in which one can sunburn is indeed news to me. Very interesting and not something I initially considered. I’m going to have to test this out and see what happens as I continue on my quest to live a healthier life. I’ll try to remember to post my results!

        1. My experience was the same as Kelda’s. I started eating primally this May and I spent more time in the sun this summer with the least burning than I ever remember. I usually burn in 15-30 minutes and I was able to work my way up to 4-5 times weekly 1 hr walks at noon, no sunscreen. I’d get slightly pink which would fade to tan the next day.

        2. Same with me. I can withstand the sun at almost triple the rate now since going primal. And when I did burn, it hurt less, and healed far faster.

      2. The effects of sun damage are not always seen immediatelty. Skin Cancer doesn’t happen overnight. Often it is exposure we had years ago, perhaps as a child that causes this sometimes deadly cancer Melanoma. Tanned skin is damaged skin, one should realize that. Foods can be a great source of Vit.D

        Certainly I wish there had been greater awareness years ago. Our daughter was not a sun worshipper yet diagnosed with melanoma at 29 y/o and died 5 1/2 months later.
        Doctors indicated most likely it was caused by the two sun burns she had, one as a child, another as a teenager.
        Better to be safe than sorry. Sunscreen is only one protective factor.
        We should protect our eyes with sunglasses, hats, clothing all are important. UVA Rays are present all year round.

        1. Very sorry to hear about your daughter, but I think you missed something fundamental about the post.

          The sun is not your enemy. Our pathological avoidance of it is one factor in many health problems, including skin cancer.

          As Mark often points out, we did not evolve with sunglasses, floppy hats, head to toe clothing, and SPF100. Our bodies are designed to absorb and use solar radiation. It’s when we avoid it habitually and then take too much at once (e.g. severe sunburn) that we cause damage.

          Tanned skin isn’t “damaged” – melanin production is a natural adaptation of our body to the sun exposure we’re getting to regulate that intake. Regular, sensible sun exposure is what we’re adapted to, not hiding indoors.

        2. so sorry for your loss Colette. I also lost someone near & dear to me to melanoma earlier this year.
          Yet I tend to think there is more to it than a specific incidence of over exposure. Or else there would be hardly anyone alive in my age bracket as we all grew up in the time of basting ourselves in baby oil & lying in the sun all day. Genetics can play a huge role in cancers also. Why some people can smoke until 70s, 80s & dont get lung disease but some don’t live past 50s. Ya, it’s probably not a good idea to fry your skin to a crisp all the time – all things in moderation.
          Cancer is a tricky, sneeky, & unpredictable foe

        3. Sorry to say your doctors were miseducated. Cancer doesn’t stay dormant for that length of time and then appear. They were just covering up their incompetence. Please don’t fall for these stunts. Question everything the doctor tells you, he’s out for your interest- your money.
          There are many good books on cancer prevention and treatment, one of the best is Flood your body with oxygen

    2. I can’t provide any definitive info on the subject, but I recall statements about the body’s omega-3 to omega-6 ratio affecting the tendency to sunburn. Primal-style eating should reduce your omega-6 consumption and increase the omega-3s, which may increase your resistance to sunburn. Just something to check into if you think it might be relevant.

      1. Kris and Peggy –
        yes the melanin is the body’s natural protection against the rays – thus they rush to the surface of the skin to protect and cause the tan. Peggy you are correct – our genetics certainly play a role – the problem is – few of us know our gene history. I myself never worried about about the sun, and tanned without a problem. Today as a
        “mature” woman my skin shows the damage done by UV Rays. Those “age” spots are the damage of years of exposure. Next time you are with an older person, notice their arms, face, hands and yet
        the underside of the arms have not a spot. I am living proof that although you tan – you are still damaging your skin. Take a look at the wrinkles, and leather look some folks have. I do not hide from the sun – I still enjoy swimming at least three-four times a week outdoors during summer months however now I wear a UV Shirt. No point in tempting nature. There was no history of melanoma in our family however a lot of breast cancer – sadly there is no cross education. The wisest thing is to take precautions.

        1. Colette,
          A reputable vitamin company Standard Process that’s been around for close to 80 years explains that the cause of skin wrinkling is from a lack of vitamin f. Most have never heard of it but the explanation behind the need for this vitamin is that excess exposure to the sun creates too much vitamin d, vit. d’s function in the body is to carry calcium to the bones. Too much d will cause most calcium to be carried to the bones at the expense of calcium deficiency in other parts of the body namely the sin. Vitamin f will restore this imbalance because its function is to carry calcium to the skin.

    3. I’d say you should just start small and gradually work up the time as you build up tolerance. Make sure as much of your skin as is prudent is exposed, so that you get more surface area working for you in your short time.

      As other posts on sunlight/vitamin D have pointed out, the fairer your skin is, the less time you “need” to create a suitable amount of vitamin D, so you may ultimately only need 15 minutes with bare arms and legs to get the benefits.

    4. Dana:

      It is the UVA Rays that penetrate and cause cancer – these are the rays used in tanning beds and are naturally present all year round

    1. Yeah, that’s the part that made me perk up most. “Primal Reconnect” or just “Reconnect” I wonder…. Exciting!

  4. What about using a tanning bed periodically in the winter? It’s not very primal, I know.
    Don’t some beds have UVB only? Is that safe, or does that come with a host of other problems?

    Is it enough to supplement with vitamin D and eat lots of fish in the winter?

  5. I remember a lecture at cancer camp by a researcher from Monash who showed a couple of slides that described the epidemiology of sun exposure.

    Basically, those data told the story that more cancer is caused than avoided by reducing sun exposure, even melanoma. That said, one needs to adjust one’s time in the sun to suit safe limits.

  6. I read about this years ago and have been very conscious of this during long car trips in the summer months. I’ll usually either have the window open or cover my arm with a long sleeve.

  7. Mark,
    I think the side topic here that also needs addressing is melatonin. While sitting in that corner office may not do much for your vitamin D, seeing normal passing of daylight helps to regulate melatonin and the sleep cycle, doesn’t it??

  8. I worked for a photographic processor once back in the days of film and spent many hours in a darkroom. And even when I came out of the darkroom I was still in a room with no external lighting.

    It always felt very unhealthy both physically and psychologically.

  9. Living up here in Canada it is actually tough to get direct sunlight during work days. I always wondered about this window issue. Thanks for resolving it!

    When I walk into direct sunlight during the winter I instantly feel better, if a little cold!

  10. Is supplementing with vit D biologically equivalent to getting D via sun exposure? I’m guessing sun exposure is probably better in some ways. Are there any studies in this area? Will Mark’s book cover this?

    1. Doh, found the answer in the “related articles”. Please disregard. Sorry

  11. Anyone have info on tanning beds? I just moved from a Mediterranean climate to a much more northern climate and am having a difficult time coping with the lack of sunlight. I’d also welcome suggestions other than tanning beds….

    1. Re Tanning Beds:

      Studies show that use of tanning beds by those under 30 y/o increase their risk of deadly melanoma skin cancer –
      Last March the FDA hearings on beds attended by researchers and dermatologists from all over the country testified to their danger. In an ideal world they would be outlawed but certainly one is free to volunteer for cancer should they wish. These reports can be found on line.
      World Health Organization and Tanning Beds or just Tanning Beds/Melanoma.

      1. I’m sorry to read of your loss, Colette. However, I respectfully disagree that sun exposure and tanning beds are dangerous and will definitely give you cancer. There’s way more to it than that. Even wonderfully healtful things in excess can be bad. Take water–several glasses won’t kill you, but drinking several gallons will. It’s the same with sunlight. Sun overexposure and subsequent buring are bad. Exposure and tanning in and of itself isn’t.

        Fear-mongering aside, in response to Mademoiselle’s question, Dr. Mercola sells a tanning bed that produces UVB, Infrared, Red, and Blue Light. You can check it out on his site.

  12. Readers of this thread may also be interested in this
    Increased UVA exposures and decreased cutaneous Vitamin D(3) levels may be responsible for the increasing incidence of melanoma.

    Resveratrol protects human keratinocytes HaCaT cells from UVA-induced oxidative stress damage by downregulating Keap1 expression.

    Lycopene-rich products and dietary photo-protection
    Vitamin D itself improves skin’s natural photo-protection as does omega 3. With all natural photo-protective strategies you must allow time for them to build up to effective levels.
    If you start now using an effective amount of D3, eliminating omega 6 industrial seed oils and increasing omega 3 intake and trying to get a daily source of lycopene/reveratrol or Green Tea by next spring you will notice you have a better resistance to UV radiation, BUT ON NO ACCOUNT should you ever allow your skin to burn.
    For those interested in using sunbeds there is some evidence short regular sessions through the winter will make life easier next summer.

  13. Awesome! I’ve always wondered about this! And awesome answer, happiness benefits (dark room versus sun lit, view vs no view) might outweigh the negatives!

  14. It is also important to note that cloudy does not necessarily mean less UV. Depending on their type and position, clouds can sometimes enhance UV levels at the surface.
    Looking forward to your new book Mark 🙂

  15. What Kitty says is correct but we must also bear in mind that Urban Ozone Pollution reduces the amount of UVB reaching ground level and this explains why 25(OH)D status varies from city to country. However where local agriculture is industrialized that also produces low level ozone pollution. As it is in amounts sufficient to reduce crop yields, it’s also sufficient to contribute to Demographic differences and trends of vitamin D insufficiency in the US population
    Wherever you live, it’s important to get 25(OH)D level checked and to adjust sun/uvb/supplement regime to ensure a reserve of stored vitamin D is always available to power immune function.
    Only above 40ng/ml can we be sure daily needs are met, only between 50ng/ml~60ng/ml does the body have reasonable stored D3 reserves.
    At latitude 32N it takes 6400iu/daily/D3 to reach around 60ng/ml to achieve vitamin D replete breast milk

    1. Thanks Ted 🙂 I’m on holidays from UV physics at the moment and too tired after the exams to go into too much detail 😛

    2. Ted,
      Before you associate ozone with pollution again I suggest you read up on the benefits of oxygen and ozone therapy. For your information without ozone we would all be dead by now. Ozone is the breathe of life and keeps the planet clean, that’s why municipal water supply agencies use it- to purify the water.
      Look at Flood your body with oxygen.

  16. Am new to this blog so I hope am not repeating comments elsewhere on the posts. Two things:
    1. from an architecture/human health standpoint, the more natural daylighting and fresh air in your homes and offices, the better. Ideal if south and west-facing windows can have adjustable exterior shades on them to prevent overheating and glare, but indirect daylight is the healthiest on your eyes and least energy-consuming for the planet. Plus a view out a window allows your eyes to periodically readjust to distant vision – also healthier for them. Artificial light consumes fuel both to produce the electricity to run it and also to cool the building from the heat it gives off (often, ironically, even in winter). Eyes and brains do suffer strain from fluorescent lighting, in my opinion, and more research should be done. However the implications would conflict with the general ‘green’ push to replace incandescent with fluorescent, and so no one that I am aware of is pursuing it.

    2. Regarding sunscreens – there has been research that shows that over the decades that we have been slathering it on that a) the overall incidence of skin cancers has not really gone down; and b) the incidence of hormone-related cancers (breast, uterine, testicular, etc.) has gone up. Most sunscreens block the rays using chemicals (the ones that sound like gasoline ingredients, like methyl-cinnamate, etc) that penetrate the skin and mimic female hormones inside the body, wreaking havoc on systems in both men and women. Sunscreens that use only physical blockers that sit on the skin (titanium dioxide, zinc oxide) apparently do not do this, so are much better. Would be worth addressing this in your upcoming book…….

  17. Thank you for answering all of my questions. It was very easy to get to your site and find the information i needed. Im new to computer technology as i just got my first laptop in September 2012. I was also looking for information as your reader above was regarding artificial ‘DAYLIGHT” bulbs. Just wondered if they worked at all.

  18. What about if you’re in front of the window at work but there is no direct sunlight coming right at you? My desk is right near the window but I never get directly hit by the sun. Should I wear sunscreen to protect against indirect UV exposure?

  19. i had an retail garment shop in which we have a big glass in frount of my gate inorder to display my cloth on that.The problem is that sunrays directly comes on that glass on which we display and if we should not replace the cloth which we display on it discolour all that through sunrays.So how should i protect from that? pls replie

  20. would west facing windows of a condo be as hot as the south facing? I live in south facing condo now and it is extremely hot even with film on inside of windows and blinds and curtains closed. I am looking at purchasing a west facing condo but need to know if it would be as equally hot as the south.

  21. Am I wrong in saying that in order for Vitamin D to metabolise in our bodies we need calcium and visa versa, so little benefit is gained by taking a supplement of one or the other?

  22. I’d like to hear what you say about sunlight through glass making me severely fatigued. I may have MS, I can tolerate being in sun easier than I can tolerate sitting in a chair by the window or a car. I feel like my body shuts down, limbs get heavy, I fell asleep waiting for a stop light yesterday. I often get a migraine with it, and it takes a few days to recuperate even if I havent gotten a headache from it. I have searched to no avail as to what is going on with UVA, I do have low Vit D. Your thoughts?!

  23. I’m like a vampire in that I want no UVA exposure at all. I don’t believe Vitamin A benefits from the sun can’t be found elsewhere and I completely disagree that sunlight improves the mood. Knowing what UVA does to skin, I want nothing of it. Is there a blog for that because I’m definitely in the wrong place. I don’t wear sunscreen because I’m not supposed to be exposed at all.

    Question: should I get only northern exposure apartments and office windows? Can one measure the indoor bouncing around of UVA after it gets through windows? Too many ppl say on the Internet that there’s a problem if you’re face is being directly hit by sunlight through a window. But that’s stupid. Of course you wouldn’t let that happen. I’m referring to the scatter effect once the rays get inside the room.

  24. Thanks Mark. You put the final piece of my puzzle together. I suffer from diurnal variation with morning depression. Just did a lot of reading about it and morning sunshine has come upconsistently as considerably a helper.
    So, then, the last bit came in- I was about to shift to a bedroom in my house which gets early morning eastern sun. Ive pulled the bed in that room over right under the window. My plan being, I will sleep right under the window with blinds open, and allow myself to be bathed in early morning sunlight for a couple hours.
    Something made me wonder-about window glass possibly affecting the quality of the sunlight.
    Due to your help, Im abandoning this plan, and shall seek direct early sunlight somehow.
    Thanks for saving me lots of time and waste-and potential danger.
    From Sooz