Sunbathe between 10 and 2 for optimal vitamin D production
Sun exposure at higher latitudes before 10 am or after 2 pm will cause UV-A rays to burn the skin before adequate vitamin D3 from UV-B is produced in the skin
So, if you’re out early in the morning or late in the day, or only getting your sun through the car or office window:
- You get lots of tanning (free radical-producing) UV-A rays. Increasing your risk of cancer if that’s your only sun intake and you fail to protect your skin. Note also that UV-A can even break through cloud cover and pollution and do its damage to skin.
- UV-A and UV-B photons can both be DIRECTLY absorbed:
By DNA: which can result in skin lesions;
By chromosomes: present in skin cells
This absorption creates reactive oxygen species (ROS), which can directly and indirectly damage DNA. Human cells have inherent systems to protect against ROS damage from exposure to sunlight, including antioxidants and DNA repair mechanisms, but these systems can be overwhelmed.
What's the difference between UV-A and UV-B rays?
UV-A (320-400 nm) Tanning Rays Cause INDIRECT and DIRECT DNA Damage |
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95% of UV raye / Causes a little immediate sunburn / long-term premature aging and some skin cancers Penetration ability (UV-A’s longer wavelength has lower energy but greater penetration ability than UV-B)
UV-A rays are pretty constant. During all daylight hours throughout the entire year; UV-A rays are tanning rays. UV-A oxidizes pre-existing melanin from melanocytes (skin’s melanin-producing cells), which in turn creates the tan color in the skin;
Damage caused by UV-A rays
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Excited Chromophore* (UV-A + Chromophore ) + 3O2 → Chromophore + 1O2 (singlet oxygen)
1O2 + Intact DNA → 3O2 + Damaged DNA
Naturally protective mechanisms against oxidative stress caused by UV-A include:
- The skin pigment melanin is a natural “sunscreen”.
Melanin, the primary color determinant of skin, hair and eyes, is produced by melanocytes (cells found in the basal layer of the epidermis, eyes, hair, also inner ear, and brain) by UV-B radiation;
Melanin absorbs UV-A and UV-B. UV-B’s direct damage to cell DNA/RNA. Melanin is transferred into melanosomes, organelles of the skin’s epidermal cells, where by efficiently absorbing the sun’s UV rays they protect the nuclear DNA/RNA from possible mutations caused by UV.
Melanin is composed of a chromophore (and attached protein) and when UV-A rays excite a chromophore that is unable to quickly convert UV-photon energy into harmless heat, ROS are produced.
- Antioxidants:
Adequate Vitamin D levels (dietary or formed in the skin by UV-B rays).
The adequate presence in the skin of other antioxidants. E.g. vitamin A /retinol, vitamin C, resveratrol and other polyphenols, vitamin B3, vitamin E, CoQ10, and astaxanthin can neutralize ROS.
- Essential fats ( omega-3 and omega-6)
UV-B (280-320 nm) – Vitamin D-making Rays |
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5% of UV rays / Mostly absorbed by ozone layer / Has both beneficial and harmful health effects BENEFICIAL EFFECTS OF UV-BUV-B helps skin produce vitamin D3 – a potent defense against melanoma. Melanoma cells convert vitamin D3 to CALCITRIOL, which causes growth inhibition and apoptotic cell death in vitro and in vivo. And conversely, research shows that increased UV-A exposures together with inadequately maintained cutaneous vitamin D3 levels will promote melanoma.
Vitamin D – “The Sunshine Vitamin” UV-B also stimulates production of Melanocyte Stimulating Hormone (MSH). Important in weight loss and energy production. UV-B RAYS CAN ALSO CAUSE DAMAGEDelayed tanning is the primary cause of sunburn and DIRECT DNA damage causing skin cancer / premature aging.
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UV-B photon is DIRECTLY absorbed by DNA (DNA has a much lower absorption ability for UV-A). DNA is able to efficiently transform >99.9% of the photons into harmless heat (via a photochemical process called internal conversion), but the remaining <0.1% create an excited state that can cause a disruption in the DNA strand (thymine base pairs next to each other in genetic sequences bond together into thymine dimers), which reproductive enzymes cannot copy. Only UV-B can cause DIRECT DNA damage.
- Leads to SUNBURN. Damage from the untransformed <0.1% UV-B is able to cause sunburn, a painful warning signal that DNA damage is occurring to cells being DIRECTLY illuminated by UV-B rays,which can lead to basal cell carcinoma and squamous cell carcinoma on the skin if damage is not immediately repaired. No such warning is generated from INDIRECT damage.
- Increases MELANIN production (commonly known as a suntan). DIRECT DNA damage by UV-B stimulates melanocytes (certain skin cells) to produce melanin, a brown protein pigment metabolized from tyrosine, that protects against overexposure to UV radiation by absorbing UV energy and dissipating it as harmless heat, and also colors the skin. The tan resulting from increasing melanin production takes about two days to develop, but is longer-lasting and less harmful than the one obtained from UV-A.
- Responsible for only 8% of melanoma cancers
UV-B ray intensity is affected by various factors
- Latitude. Most of the US is between 30° and 45°latitude, which for several months a year, has insufficient UV-B sunlight to produce optimal D level:
30° (N and S). Insufficient UV-B 2-6 months of the year, even at midday; only Florida and S. Texas are below 30°N in mainland US
40°. Insufficient UV-B during 6-8 months of the year; includes Oregon, Idaho, Wyoming, Nebraska, Iowa, S. Dakota, N. Illinois, Wisconsin, N. Indiana, Michigan, Ohio, Pennsylvania, New York and the New England States;
45° (far N or S). Even summer sun is too weak. Includes most of Washington, Montana, N. Dakota, and northernmost parts of Minnesota, Wisconsin and Maine;
- Altitude. UV-B is stronger at higher altitudes;
- Glass. Only ~5% of UV-B goes through glass;
- Ozone layer, clouds, smog or fog. Full cloud cover decreases UV-B ~50%; stratospheric ozone depletion increases;
- Time of day/Sun’s position in sky – More UV-B rays reach earth at midday than in the morning or evening. When the sun is high in the sky around noon, its rays have a shorter distance to travel through the Earth’s ozone layer to reach the surface of the Earth, which reduces absorption by the ozone layer and so increases amount of penetration. Conversely, when the sun’s rays are at an oblique angle early and late in the day, they have a further distance to travel through the ozone layer, and so have a more reduced intensity than when rays hit directly. When the sun goes down toward the horizon, UV-B is filtered out much more than UV-A
