halbert said...
So, it doesn't take much sunlight to generate enough Vit D. Hours in bare skin is not required.
Some folks say just enough to get the 1st hint of pink is more than enough, which is not very much depending on your skin tone and where you live. Another factor is how much skin is exposed. Being on the beach on the Gulf Coast in July in a bathing suite, I'm thinking most folks will require very little time.
FWIW, Mercola says: "
The first few days, you should limit your exposure to the sun to allow your body's melanocyte cells to rev up the ability to produce protective pigmentation that not only gives you a tan, but also serves to help protect you against overexposure to the sun.
If you are a fairly light skinned individual that tends to burn, you will want to limit your initial exposure to a few minutes, especially if it is in the middle of summer.
The more tanned your skin will get, and/or the more tanned you want to become, the longer you can stay in the sun. If it is early or late in the season and/or you are a dark skinned individual, you could likely safely have 30 minutes on your initial exposure. If you are deeply pigmented and your immediate ancestors are from Africa, India or the Middle East, it is possible you may not even have to worry about
the timing of your exposure.
Always err on the side of caution however, and let it be your primary goal to never get sun burned.
You can use a moisturizing, safe, NON-SPF cream to moisturize your skin, or use something as simple as organic coconut oil to moisturize your skin as this will also benefit you metabolically. Remember if the moisturizer you use has an SPF value, it will block UVB rays and will not allow your body to produce any vitamin D. The rest of the day, you can spend in the shade, wear clothes, and, if you still want to be in the
open sun, use a non-toxic lotion with SPF15 for uncovered skin. Just be sure to be on the safe side of burning!
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The first step is to determine the latitude and longitude of your
location. You can easily do this on Google Earth, or if you are in the U.S. you can use the TravelMath Latitude Longitude Calculator to find your latitude and longitude i. Once you have obtained that you can go to the U.S. Navy site to calculate a table to determine the times and days of the year that the sun is above 50 degrees from the horizon ii. Please view the video at the top of this page. The URL for the US Naval Observatory Azimuth table is http://aa.usno.navy.mil/data/docs/AltAz.php
For a more detailed understanding of this you can visit the University of Colorado State's page iii that discusses this in more detail. If you read the paper you will see that there are other factors, such as ozone concentration, altitude, air pollution, ground covered by snow or ice, and cloud cover that also contribute to the amount of UVB that is ultimately reaching your skin.
Translated to the date and time of some places on the globe, it means for example: In my hometown of Chicago, the UVB rays are not potentially present until March 25, and by September 16th it is not possible to produce any vitamin D from the sun in Chicago. Please understand it is only theoretically possible to get UVB rays during those times. If it happens to be cloudy or raining, the clouds will also block the UVB rays.
This is one of the reasons I now spend most of my winters in the sunshine state of Florida because in the center of the state there are more than two extra months of UVB as the sun doesn't disappear for winter until October 23 and comes back again much earlier, around February.
When NOT to Tan
From a health perspective it doesn't make much sense to expose your skin to the sun when it is lower than 50 degrees above the horizon because you will not receive any valuable UVB rays, but you will expose yourself to the more dangerous and potentially deadly UVA rays. UVA's have a longer wavelength than UVB and can more easily penetrate the ozone layer and other obstacles (like clouds and pollution) on their way from the sun to the earth. UVA is what radically increases your risk of skin cancer and photoaging of your skin. So while it will give you a tan, unless the companion UVB rays are available you're likely doing more harm than good and should probably stay out of the sun to protect your skin.
During the times of the year when UVB rays are not present where you live you essentially have two options: You can use a safe tanning bed or you can swallow oral vitamin D3.
Avoid Tanning through a Window as it Will Increase Your Skin Cancer Risk
Because the UVA has a longer wavelength, it penetrates materials more easily, such as the earth's atmosphere and window glass which will effectively filter out the majority of UVB radiation, but only minimally filters out UVAs. What's the significance of that, you ask?
It's important to remember that vitamin D3 is formed from exposure to UVB rays, whereas UVA radiation actually destroys vitamin D. This helps keep your body in balance; it's one of the protective mechanisms your body has to avoid overdosing on vitamin D when you're outside. However, when you're exposed to sunlight through windows -- in your office, your home or your car -- you get the UVA but virtually none of the beneficial UVB.
This can lead to significant health problems, because in addition to destroying vitamin D3, UVA's also increase oxidative stress. UVA is one of the primary culprits behind skin cancer, and it increases photo aging of your skin. It's also what causes you to tan. You can actually get vitamin D without significantly darkening your skin, because the UVB wavelength does not stimulate the melanin pigment to produce a tan.
Normally, of course, when you get tanned from outdoor sun exposure you're getting both UVA and UVB at the same time, so it's not a problem. But when you are indoors and expose yourself to sunlight filtered through window glass, you are increasing your risk of a variety of conditions, primarily skin cancer, because the UVA's are effectively destroying your vitamin D3 levels while you're getting none of the benefits from UVB, and this can significantly increase your risk of skin cancer. This is one of the reasons why many that drive long hours in their cars develop skin cancer on the arm next to the car window..........".
articles.mercola.com/sites/articles/archive/2012/03/26/maximizing-vitamin-d-exposure.aspxAnd
articles.mercola.com/sites/articles/archive/2016/08/08/low-vitamin-d-levels.aspxSomebody said...
Sunscreen Versus the Vital Need for Vitamin D
Although the horror stories of excess sun and subsequent skin cancer have scared most Americans and Brits into the shadows, Louis Levy, head of nutrition science at Public Health England, told BBC Radio that people using sunscreen as recommended will not get enough vitamin D.
"This is a change in advice, previously we have said that babies from [6] months to years should have a supplement and only those people at risk of deficiency should take a supplement.
Previously we felt that everybody would get enough from the sunlight. This is new advice based on evidence looked at over the last five years. When you go out, you do need to have short bursts without sunscreen and make sure that you don't get sunburnt."7
In America, even the National Institutes of Health (NIH) admits that sunscreens block vital vitamin D-producing sunrays, and suggests that a little sun without sunscreen is good. On its webpage, the NIH says:
" … Approximately [five to] 30 minutes of sun exposure between 10 [a.m.] and 3 [p.m.] at least twice a week to the face, arms, legs, or back without sunscreen usually lead to sufficient vitamin D synthesis."