Having been doing my own online research for research papers on VitD for the last 5 years and there is simply thousands of articles related to VitD or factors that can vary the amount of UV-B you get, Google in this case is your friend if you want to investigate and be more informed yourself, but I thought I'd share what I have found so far.
The reason for doing so is simply that as an office based swm stuck in front of a computer for upto 14hours a day, I started noticing my health deteriatoring and having no success with the dr's I started looking elsewhere. When I say health, I mean lack of energy, no desire to jump out of bed in the morning, aches and pains, putting on weight, feeling depressed that sort of thing although I know alot of people will say thats just part of getting old, I disagree!
Basically VitD is essential for healthy a life, in 2010 the charity the Wellcome Trust discovered whilst reverse engineering the human genome there are 2776 Vitamin D Receptors (VDR's) in the human genome, the vast majority concentrated around the immune system genes. www.wellcome.ac.uk/News/Media-office/Press-releases/2010/WTX062545.htm
Now you can get VitD from food but in very small quantities, foods that contain it are egg yolks, reindeer meat, and wild caught oily fish. 0101.nccdn.net/1_5/3a0/1e8/00e/Cannell-Vitamin-D-study.pdf
It also adds weighting to the arguement about eating seasonal local foods as well, for example the northern countries Norway Sweden, Greenland etc traditionally eat more oil fish for example.
The UK and US govts have a Vit D RDA guideline of 400 UI (Units International - its a french measurement).
Anyway becuase our modern hectic lifestyles which mainly consists of being indoors out of the sun and the Govt advice for the last decade of stay out the sun etc as created what I would call a health epedemic (strong words I know but time and research will prove me right). To understand why the UK Govt put this message out you need to trace it back to its roots. This advice of staying out of the sun comes from Australia and for those who did history will know that the UK used to ship their criminals off to Australia yet if you look at the native Aborigines there are dark skin so theres a clue there as to why (white) Australians were getting skin cancer.
Now if you consider that virtually all mammals infact all life including plants need the sun, it seemed counter intuitive to slap on the sunscreen so I started to dig more.
Having found this site www.uvguide.co.uk/uvinnature.htm it transpired that Reptiles also suffer from a sort of Rickets only they call it Metabolic Bone Disease/Syndrome exoticpets.about.com/cs/reptilesgeneral/a/metabolicbd.htm
Now these Reptile owners love their pets so some of them organised themselves to start looking into this problem and also started looking at the existing heat lamps. This led them to start measuring the UV-B from around different parts of the world results shown here in this graph for Dec 2005 www.uvguide.co.uk/images/decsolstfairweather-800px.gif
and here for Wales during June 2005 in Wales www.uvguide.co.uk/images/solarUVBJune05Chart.gif. You can see in Wales the most amount of UV-B goes up to 350uW/cm2 yet in Australia during their summer it gets up to 450uW/cm2 so the Australians get higher levels of UV exposure and thus is it any surprise they get higher rates of Skin Cancer?
UV-B is what is needed, specifically the wavelength 297nm, it should also be noted that the UK definition of UV-A and UV-B wavelength range varies to the US definitation of UV-A and UV-B wavelength ranges as well just to confuse matters.
Anyway having established UV-B is what reptiles need, I started looking elsewhere for human info and confirmed that UV-B exposure to the skin is needed to help produce Vit D. www.direct-ms.org/sites/default/files/Engelsen%20vitamin%20D%20synthesis.pdf
This paper from Norway confirms that at 70 degrees latitude VitD synthesis is absent for 5 months of the year.
Theres a handy calculator where you can put in your longtitude and latitude and work out how much Vit D you might produce zardoz.nilu.no/~olaeng/fastrt/VitD.html, you can get your Long/Lat from here touchmap.com/latlong.html just zoom in to where you live, put a blue marker on your position, then click on the blue marker again to see the Long/Lat in the popup mousetip. Put in the date, select the type of weather it is, work out the Ozone and you get a better idea of how much Vit D you might produce, but the link only concentrates on atmospheric Ozone, it doesnt measure groundlevel Ozone which is the smog alert you see on the BBC weather during the summer.
Car fumes reacting in the sunshine produce low level Ozone which can also trigger Asthma attacks for some.
Now it should be noted that whilst UV-B reflects off manmade surfaces like roads & concrete buildings becuase of the vehicle polution, the UV-B exposure to the skin in a City/Town can be upto 3 times less than in the countryside. So whilst plants absorb alot of UV-B for themselves which means we dont get it reflected back onto our skin when sunbathing in the garden the overriding factor here is the car pollution that reacts in the sun to produce Ozone which then blocks UV-B from getting down to the ground level on our skin.
In some respects if you sunbath in your garden in a town or city you will need to do it for upto 3 times longer than if you were in the countryside away from vehicle pollution and dont forget airports in this case as well.
With regard to sunbathing safety, the current advice given out by some charities is get some sun but dont burn or go red. Now it should be noted the body produces melanin (what makes us go brown) when exposed to UV-B. en.wikipedia.org/wiki/Sun_tanning#UVB www.ncbi.nlm.nih.gov/pmc/articles/PMC524044/
UV-B creates the melanin or pigment, UV-A reactivates the melanin. Sunbeds in tanning salons typically output UV-A. It should also be noted once you have a full good tan, the skin will reflect 99% of UV light protecting your further. en.wikipedia.org/wiki/Melanin and en.wikipedia.org/wiki/Photoprotection "Melanin is such an efficient photoprotective substance that it dissipates more than 99.9% of the absorbed UV radiation as heat. [2] This means that less than 0.1% of the excited melanin molecules will undergo harmful chemical reactions or produce free radicals."
Looks like nature has also created our own sunscreen as well!
Anyway where the science isnt clear is exactly how the Vit D is produce, whilst is generally stated the skin produces Vit D its more complex than that and again other advice from the Govt on Cholesterol reduction comes into play here. Firstly its not known if its the skin that produces that Vit D or the sebum (oil secreted by the skin) reacting in the UV-B and then being absorbed back into the skin that is creating the 1st form of Vit D, this hasnt been researched adequantly, so daily showers washing off our natural oils could also be hindering our abilities to produce 1st stage Vit D or Pro/Pre Vitamin D. Reason I say this is simply this, if a suntan is reflecting 99% of the UV, how can the body still produce Vit D? Unless its the skins own oils (which we normally wash off in daily showers) reacting in the sun like it does for other animals like cats, dogs, & sheep for example and then being absorbed back into the skin that then enables the body to process it into the finished VitD. Needs more medical studies here but as most of this is paid for by BigPharma including sponsorship of medical degrees at Uni which enables them to influence the curriculmn, only charities like the Wellcome Trust and Cancer/Skin charities can do this.
Anyway once its absorbed into the skin it travels down to the liver where the liver takes about 12-14days to convert it into another form of VitD, but the liver needs Cholesterol to do this which comes from fat. Now bear in mind Alcohol can damage the liver, avoiding alcohol for a few weeks after being in the sun say on holiday (I know I know) could be even more beneficial to us. Again no research on this, but bear in mind Alcohol damages the liver so consuming alcohol could be like shooting ourselves in the foot with regards to our helth, its already been noted than Alcohol increases the incidence of Cancer in humans so is becuase we cant produce enough Vit D to boost our immune system? The Kidneys also process the VitD before it becomes fully fledged Vit D at which point it becomes beneficial to the human body and if the levels are high enough only then will the body also start to store it for those days when the weather isnt good and we cant get any sun.
Now its been noted in one little known study that Cholesterol levels go down in British Gardeners during the summer months. I originally found this from this link en.wikipedia.org/wiki/Cholesterol but its since been removed but other sites have picked up on it like this one www.hivehealthmedia.com/5-reasons-vitamin/ but it should be noted its accepted medical knowledge that Cholesterol is required to produce Vit D so your low cholesterol diet could also be inhibiting your health ie if you dont have enough cholesterol you cant produce enough Vit D.
It should also be noted that rich people live 7 years longer than the average www.telegraph.co.uk/health/healthnews/7205647/Well-off-people-live-seven-years-longer-than-those-in-poorer-groups.html Why is this? I'd say a number of factors but how about the fact they probably spend more time in the sun as well?
Another point about vitamin D is it isnt actually a Vitamin (another medical mistake), its a steroid hormone which boosts the body. Have you ever wondered why during the summer months your hair and nails grow faster than during the winter months? I'd say VitD levels is why, in fact the rate of hair and nail growth I would say is an indicator of your VitD levels in your body albeit a slow indicator but an indicator nonetheless.
Anyway it looks likes the world is realising we do need sunshine after all and that our modern lifestyles could actually be harming our health. You only have to look at the number of new news stories on the subject like here www.google.co.uk/search?hl=en&gl=uk&tbm=nws&btnmeta_news_search=1&q=vitamin+d&oq=vitamin to see that more and more charities are finding positive results for it.
Also if you didnt know, there is actually a number of different types of Vitamin D. D2 is the plant derived form which is toxic at far lower doses than D3. You get D2 by exposing some plant forms like Mushrooms to UV light but this isnt commercially viable, D3 is the most active form of VitD and most beneficial to the humans and other animals including reptiles.
I've also been taking 10,000ui as a daily supplement on a daily basis for the last 3 years and can say my health has improved enourmously, more energy, no aches, better concentration, I just couldnt recommend it enough.
The East Germans and Russians knew about Vit D during the 50's when they experimented with it during the olympics for example, associations.sou.edu/aaaspd/2011SANDIEGO/Workshops11.html#4
www.vitamindsportsbook.com/new-book-athletes-edge-faster-quicker-stronger-with-vitamin-d-john-cannell-will-vitamin-d-become-the-new-performance-enhancing-drug/
The thing to remember though is its a steriod human which will boost your immune system and will be very beneficial for the human body.
Another point to make is that you also need to up your magnesium levels and calcium levels, otherwise the body cant utilise it as effectively as possible.
www.vitamindcouncil.org/about-vitamin-d/vitamin-d-cofactors/magnesium/
Magnesium is best taken by eating your greens (where have you heard thatbefore), what makes plants green is Chlorophyll, and a primary compenent of chlorophyll is magnesium. Magnesium supplements will have you go to the loo faster than you really want to, so getting the natural form of it ie vegetables or greens is the best source. Believe it or not there is also more calcium to be had from eating ones greens than in milk as well and if you live in a hard water area ie high in calcium or chalk your health will benefit more if you have the right ratio of magnesium as well.
Unfortunately alot of the medical profession are not as up to date as they could be on VitD and becuase they tend to focus on one specific area they dont always see the connections from other dietary sources as well, its a flaw in the way science work ie they dont alway take a step back and see the bigger picture, but if you have any questions about it, google is your friend as a starting point and if you want the best for you kids, ie help them achieve the academic potential and set them up with good health etc etc you should look into it for yourself and draw your own LOGICAL conclusions, but ensure you know what form of VitD is being referred to ie D2 or D3 (the NHS has tended to prescribe D2 in the past and most medical references unless specifically mentioned tend to be look at D2 as well).
Some other benefits of Vitamin D3 to hopefully whet the appetite!
Conception & IVF? www.vitamindwiki.com/tiki-index.php?page_id=1031
Pregnancy www.bbc.co.uk/news/10486310
donmatesz.blogspot.com/2009/10/new-study-vitamin-d3-supplementation.html
Depression www.netdoctor.co.uk/interactive/news/children-with-high-vitamin-d-levels-less-likely-to-be-depressed-id801270222-t116.html
Cancer www.cancer.gov/cancertopics/factsheet/prevention/vitamin-D
scienceblog.cancerresearchuk.org/2009/09/21/vitamin-d-and-cancer-survival/
Flu and Asthma www.reuters.com/article/2010/03/19/us-vitamind-study-idUSTRE62I3MK20100319
www.newsday.co.zw/article/2011-11-18-doctors-on-call-vitamin-d-alleviates-asthma
www.ourcoloradonews.com/health/ages/why-everyone-needs-a-little-more-vitamin-d/article_c08d91f4-3ff9-11e1-805a-0019bb2963f4.html
The bottom line is (if you have made it this far ;-) ) is VitD3 is good for you even Eli lilley carried out a study on Vit D with their own drugs and concluded most of their drug treatments work even more effectively with Vit D3! edrv.endojournals.org/content/26/5/662.full
Finally, I've been taking 10,000ui of D3 on a daily basis for the last 3 years and have followed the sort of diet a T2 diabetic with a gluten intolerance would follow, ie no sugar (just honey becuase at least it contains minerals) and no cereals/grains or any sorts. The result is I have lost weight as well and for a block who sits in front a computer for anything from 10-14 hours a day nearly 7 days a week, has a cooked breakfast everyday, by cutting out my sugar which I noticed made me binge more on food, I have lost weight without trying! In fact by eating fatty foods, getting as much sun as possible its been too easy to get into shape which aint bad for a bloke nearly touching 40 and I have no bear belly!
Anyway I thought I would share what I have learnt so that it can be of use to you (if you havent switched off by now)! ;-)