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It depends on the glass. Vitamin D synthesis needs UV in the range 285 to 315nm. At least part of that will be absorbed by normal glass.
Soda Lime Glass - A term used to describe the base glass type used for most clear, colored and patterned glass types. This is because of the use of soda, Na2O, as a fluxing agent to mix with sand (silica) to allow the batch to melt at lower temperatures more quickly and economically and the use of lime, CaO, to improve the chemical durability of the glass. In order to make these glasses more heat resistant and increase their physical strength they must be tempered.
The photobiology of vitamin D--a topic of renewed focus. [Article in Norwegian]Moan J, Porojnicu AC.Avdeling for strålingsbiologi, Rikshospitalet-Radiumhospitalet, 0310 Oslo. email@example.comThe sun is our most important source of vitamin D. Exposure to solaria, in sub-erythemogenic doses, also gives large amounts of this vitamin. The ultraviolet radiation in these sources converts 7-dihydrocholesterol to previtamin D3 in the skin. Furthermore, heat isomerization to vitamin D3 takes place, then transport to the liver and hydroxylation to calcidiol, which is transported to the kidneys and hydroxylated to the active hormone calcitriol. The vitamin D3 status of the body is supposed to be reliably imaged by calcidiol measurements. Calcidiol levels above 12.5 nmol/l prevent rickets and osteomalacia, but optimal levels are probably higher, in the range 100-250 nmol/l. A daily food intake of 100-200 microg vitamin D3 (50-100 g cod-liver oil), or a weekly exposure to two minimal erythemal doses of ultraviolet radiation (20 to 40 minutes whole body exposure to midday midsummer sun in Oslo, Norway), will give this level.An adequate supply of vitamin D3 seems to reduce the incidence rates or improve the prognosis of several cancer forms, including prostate, breast and colon cancer, as well as of lymphomas.Several other diseases are related to a low vitamin D3 status: heart diseases, multiple sclerosis, diabetes, and arthritis. The action mechanisms of vitamin D are thought to be mainly related to its known cell-differentiating and immuno-modulating effects. Even though most of the 250 annual death cases from skin cancer in Norway are caused by sun exposure, we should, in view of the health effects of ultraviolet radiation, consider modifying our restrictive attitude towards sun exposure and use of solaria.Tidsskr Nor Laegeforen. 2006 Apr 6;126(:1048-52.http://www.flipimages.co.uk/imageslandscapes/fjordhouse.jpg
Rather than taking the risk of exposing your skin to unknown UV levels you might want to try eating a varied diet or taking vitamin pills. The other thing to remember is that excess vitamin D is rather toxic- it's used as a rat poison.
Abstract. The solar UV transmitted through automobile glass was measured in the field in two cars using a spectroradiometer. The two cars were identical except that one of the cars had all of the windows (except the windshield) tinted. The measured spectral erythemal UV on a horizontal plane with the windows fully closed was reduced in the tinted car by a factor of 42 when compared with the erythemal UV measured in the untinted car. The ambient UVA irradiances at various locations within four different makes of car and a tractor were also measured with a broad band UVA hand-held meter. The average normalized daily UVA exposure (measured with a broad band UVA meter) was 1.3 times higher in a large family sedan when compared with that in a small hatchback and the UVA exposure in a car with tinted windows was 3.8 times less than in a similar untinted car.
Journal of the American Academy of Dermatology article offers information about the recent development in sun protection provided by window and automobile glass, and sunglasses.In the car, at work or walking to and from a store, you can’t escape the sun’s ultraviolet (UV) rays. However, new research about the transmission of UV light through window and automobile glass and through sunglasses, has led to developments that can help protect people from the sun.“People should realize that even during everyday activities they are receiving incidental sun exposure which harms the skin as it accumulates and can result in premature aging, wrinkles and even skin cancer,” said dermatologist Henry W. Lim, M.D., chairman of the department of dermatology, Henry Ford Hospital in Detroit, Mich., and co-author of the Journal of the American Academy of Dermatology article entitled, “Photoprotection by window glass, automobile glass and sunglasses.” “Dermatologists and manufacturers of glass products and sunglasses are continually working to find better ways to decrease the amount of UV radiation being filtered through these items to the skin and eyes. These advances are helping to reduce the amount of UV exposure that a person receives on a daily basis.”UV radiation from the sun comes in two forms: ultraviolet A (UVA) and ultraviolet B (UVB). UVB has long been associated with sunburn while UVA has been recognized as a deeper penetrating radiation that contributes to premature aging and wrinkle formation. Both of these types of rays have been linked to the development of skin cancer. More than 1 million new cases of skin cancer are diagnosed each year.Window Glass and PhotoprotectionWindow glass filters out UVB rays, but UVA rays are still transmitted to the skin through the panes. The type of glass and the type of coating on the glass can affect the percentage of UV radiation that is transmitted to the body.Most residential buildings have one of three types of glass: clear, tinted or reflective. Of these three, reflective glass, the kind that eliminates the ability to see the interior of a building from the outside during the day, minimizes unwanted solar heat gain and reduces UV transmission to less than 25 percent. This means nearly one-quarter of the UV exposure, exclusively the longer wavelength UVA, is reaching the inside though, remarked Dr. Lim.“Most Americans spend 80 percent of their day indoors at work or school,” stated Dr. Lim. “With the new trend in architecture toward more and larger windows in buildings, protection from UV exposure when indoors has become an important issue for not only the cost-effectiveness of cooling a building, but also for the health and safety of the employees who work within it.”Recent developments in window glass include low-emissivity (low-E) glass which has a special surface coating between layers of antireflective glass. This type of glass reflects up to 70 percent of solar heat and reduces UV transmission through the panes to 20 percent.To protect the skin from the damaging rays of the sun when working indoors, it is important to: arrange workspace so that the body is not in direct sunlight; and use blinds or shades on the windows during peak sun hours.Automobile Glass and PhotoprotectionIn studies of UV exposure in cars, it was shown that the parts of the driver’s and passenger’s bodies closest to the window received the greatest UV exposure. Side and rear windows are usually made from non-laminated glass, allowing a significant amount of UVA to pass through to the passengers in the car. Most windshields are made from laminated glass, the type of glass designed to prevent fragments from shattering onto the occupants during an accident and which can filter both UVB and a large portion of the UVA rays.Tinting automobile glass is an option that allows 3.8 times less UVA light to be transmitted to the interior of the car as compared to untinted window glass. In a 2004 study of UV transmission and color tint, grey tinted laminated glass provided the highest UV protection with only 0.9 percent of UVA light transmitted versus 62.8 percent transmitted through non-laminated clear glass. People who are considering tinting their windows should take their car to a professional auto detailing shop, in order to ensure that the tinting meets the federally mandated 70 percent of minimum visible light transmittance through the windshield.“Obviously UVA exposure in a car is influenced by non-glass-related factors such as position of the individual in the vehicle, direction of travel with respect to the sun, and time of day,” stated Dr. Lim. “However, the more time a person spends in a car, especially at the same time of day such as during a regular commute, can greatly affect the amount of UV exposure their skin receives.”To reduce sun exposure while driving, wear protective clothing, such as a long-sleeved shirt and pants, especially when the body is in the sun; apply sunscreen generously to any exposed skin before driving, especially the hands, forearms and face; and wear protective sunglasses to reduce glare and protect the eyes from UV exposure.
In northern areas, there is very little ultraviolet light available in the wintertime. Significant UV light is only available from the hours of 10AM through 2PM (11-3 daylight savings time). Of course, sunscreen filters most UV light. Even untinted windows filter out most UV light. Your commute to work and back in the morning and afternoon doesn't help you get the vitamin D you need!Many of us simply don't get outside in the middle of the day. Many adults don't drink milk or eat much fish. If we don't get outside and don't take vitamins, there is a very high probability that we have insufficient vitamin D.Most of our ancestors were farmers and spent most of their time in the sun. Today, we spend more and more time inside. When I was a child, parents encouraged children to play outside to get fresh air and sunshine. We had four TV channels. Today, kids have video games and over 100 channels to keep them inside. They are more likely to have karate classes or other activities that are held indoors.People are spending less and less time outside. The rate of rickets among children is triple what it was a few years ago according to some reports.Studies on people that spend a lot of time in the sun such as lifeguards and farmers show that they can have twice as much vitamin D in their blood as other people. Studies show that about 1% of the population has severe deficiency, but 25% to 50% have the lesser condition of vitamin D insufficiency.In recent years, we’ve been repeatedly advised to stay out of the sun and use sunscreen. Yet, we’re often told that vitamins pills are a waste of time, and that if we eat a balanced diet we don’t need them. If we don’t get out in the sun and don’t drink milk or eat fish, there are no other sources of vitamin D. It is the forgotten vitamin.
Vitamin D3 is a substance that is toxic in large amounts. From the 1920s, vitamin D was added to milk for human consumption to eradicate rickets; however, this was banned in Europe in the 1950s because children were suffering from overdosage.In reptiles, too much vitamin D added to the diet leads to hypervitaminosis-D, which causes kidney damage, calcification of the soft tissues, including the major blood vessels, and premature death.However, hypervitaminosis-D is not known to occur in basking reptiles (or any other species) obtaining their vitamin D from sunlight, regardless of how long they bask. This is because there are inbuilt safety mechanisms preventing overproduction of vitamin D in the skin.
conclusioneyeglasses with UV filter stamp are another price fake -every ubiquitous "normal" glass does not allow UV you can not obtain vitamin D sitting behind windowam I right?