how much outside time = enough vitamin D

[Nosy]

As we were sunning ourselves last week, I was wondering how much outside time you would need per day in order to maintain your current level of Vitamin D. Are there guidelines anywhere? I realize it would vary depending on latitude, but it would be neat to figure out how many IU you could get in x number of minutes.

[sbgrace]

I think Tanya has posted a calculator.
I believe whether the body can use the sun exposure vitamin D though really depends on individuals.
http://jcem.endojournals.org/cgi/content/full/92/6/2130
Among people in Hawaii getting abundant (good latitude) sun exposure almost all were deficient in vitamin D. The group got 28.9 average hours of sun exposure per week (22.4 hours per wk with no sunscreen; 40% never useed sunscreen. Of the 93 51% were below 30 (wayyyy low) on vitamin D levels. The mean level was 31.6 (low--40's are suboptimal). I looked a while back on the details of the study. There was almost no one above 40 in that group--I think it looks like 7 of the 93 were at 50 or above. Another 12 might be suboptimal but not low in the 40's. It seems like a very well run study (for example they used a variety of ethnic groups and skin colors as outlined and measured).


Clearly, there is more to this (genetically, habit wise perhaps in terms of showering after sunning) than just getting sun for many people. So the only way to know if you're getting adequate D through sun exposure is to have 25(OH) D levels measured.

[tanyalynn]

There's a cool calculator out there, it has inputs like lat/long, % skin uncovered (it assumes an adult, so if you're wanting to figure out a kid, you need to do your own conversions), um, amount sun/cloud, time of year, and skin type. Let me see if I can find it on DH's computer (not bookmarked here...)


http://nadir.nilu.no/~olaeng/fastrt/VitD_quartMED.html

This is it. I had a lot of fun playing around with that last year. Time of day, % skin uncovered make a huge difference.

[tanyalynn]

cross-posted with Rachelle

And yeah, there's health stuff too, it assumes healthy people. The UV light hits a chemical pre-cursor to cholesterol in our bodies, so I think those with low cholesterol are at a lot higher risk of not making a lot of vitamin D in the sun--I had depressingly low cholesterol a couple years ago, I hope/assume it's getting more normal now.

I also think that other sources are often important, the amounts that the vitamin D council talk about to get blood vit D into a good range are fairly high--doable in the summer, depending on your lifestyle and health, but a lot harder year-round.

But it's still fun to play with, and as a rough guesstimate, I think it was fairly accurate for my son (presumably my daughter as well). Either in the sun, or with an oral supp, he'd sometimes get hyper, and less time in the sun and lower amounts of supp didn't do it, but long days out in the Texas sun did make him hyper the next day. Obviously that's very inexact, but it was interesting to watch.

[SandyMom]

I thought that cholesterol connection was really interesting. And also, swimming in pools inhibits the absorption process to I guess:

It takes about 24 hours for UV-B-stimulated vitamin D to show up as maximum levels of vitamin D in the blood. Cholesterol-containing body oils are critical to this absorption process.10 Because the body needs 30-60 minutes to absorb these vitamin-D-containing oils, it is best to delay showering or bathing for one hour after exposure. The skin oils in which vitamin D is produced can also be removed by chlorine in swimming pools.

http://sites.google.com/site/natural...sting-immunity

[mom61508]

Originally Posted by Nosy

As we were sunning ourselves last week, I was wondering how much outside time you would need per day in order to maintain your current level of Vitamin D. Are there guidelines anywhere? I realize it would vary depending on latitude, but it would be neat to figure out how many IU you could get in x number of minutes.

Go here for good vitamin D info as well
http://www.vitamindcouncil.org/