Training & Nutrition - Vitamin D question
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Do you get vitamin D from sunlight or just daylight? I've always been confused by this. I have red hair, and read somewhere that red haired people are very good at synthesising vitamin D from poor light, but then I read that people with red hair fair badly with MS, because they don't tend to get enough vitamin D when younger. I'm not sure if the reasoning behind this is that they stay out of the sun, or where more sunscreen, but that would only work if it were only sunlight that caused vitanmin D synthesis.
Also, I read recently that the in the US it was advised that children were supplemented to 400 IU of vitamin D. Anyone read anything contrary to this? I seem to remember reading that excess supplimentary vitamin D can cause kidney damage.
08-11-09, 05:46 AM
I think the amount of sunlight you need to be exposed to depends on where you live and the time of the year. I live in New England and from November to February it is very difficult to get enough vitamin D from the sun. In fact during physical this past May the doctor did a vitamin d test and I was found to be vitamin D deficient. So for 12 months starting in May he prescribed 50,000 i/u of vitamin D once a month.
It is possible that too much vitamin D could cause kidney and liver damage. To the best of my knowledge vitamin D is fat soluble and is processed by the kidneys and liver. I do not have a medical background but just basing the above on what I have read.
08-11-09, 07:52 AM
Too much of anything can cause kidney and liver damage. It is a complicated process, but simply put, the liver and the kidneys are filters. The harder they are required to work, the higher the likelihood. That is why you hear on tv adds, over and over, that you should have a liver function test before taking X,Y, or Z drug. It is also one of the reasons you need to tell your physician all the medications you take, when getting a new prescription. That is partly because of adverse reactions from mixing incompatible drugs, but equally important is not overtaxing your body's filtration system.
As to the question about the 400iu supplementary dose for kids, that is well below any danger level, and probably well below any level that does any significant good as well.
The data on vitamin d is all over the map, because in truth, medical science really has no good idea on how it is used by the body, but there is lots of data supporting it's use.
Many thanks. For myself, I'm not too concerned about trying larger doses, after research, but for my kids, I'm more cautious. It would be good if there was some concrete data.
My problem is that we like in the north west of England, which is more often than not grey and rainy. In summer there can be enough sun to get the kids into, minus sunscreen, but in autumn, winter and spring it is at a premium. We have MS in our family, which is why I want to make sure my kids get enough vit D (between ages 6 and 15, the more vitimin D kids get, the less their likelihood of developing MS in later life.
I would prefer the natural route, but, again, living where we do, it's difficult.
Anyone know definitively whether it is sunlight or just daylight that sythesises vitamin D?
08-11-09, 11:47 AM
I do believe it is sunlight specifically UVB rays.
08-11-09, 04:08 PM
Some good vitamin d info here http://www.vitamindcouncil.org/
and here http://blog.nutritiondata.com/ndblog/2009/08/how-much-sunshine-does-it-take-to-make-enough-vitamin-d.html
08-11-09, 05:12 PM
My Doc recently checked my vitamin D level and found it to be low. He put me on 50,000 iu D softgels, three times a week for three months. I didn't take them the first month because it shocked me that the RDA is set at 400 iu, and he was trying to give me 50K iu.
On my next appt., he explained that vitamin D is one of the few vitamins that won't cause problems in high doses. He also explained that once the level is up where it should be, it takes just a small amount to maintain it. And about the 400 iu RDA, that's what it takes to prevent rickets disease from forming in children (where the bones become soft and bend). But 400 iu is not enough to get the other benefits D provides.
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