Science Questions

Does Sunblock stop vitamin D production?

Sun, 14th Sep 2008

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Alan, Sydney; Sean Maul, Canada asked:

You have to spend 10-20 minutes in the sun to make vitamin D. Since I moved to Australia Iíve also been told how important it is to wear sun block. My question is, does wearing sun block affect the rate that vitamin D gets formed at? Is there no difference?


Kat -  Yes it does.  For most healthy people you should be thinking about wearing the sun cream rather than worrying about your vitamin D.  The simple reason is this: sun block does block ultraviolet radiation which is the stuff that helps you make vitamin D.  Itís also the stuff that damages your skin and gives you skin cancer.  This is why in somewhere hot and sunny like Australia itís very highly recommended you protect yourself in that way.  You do only need a few minutes of sun exposure to make enough vitamin D.  Itís certainly less than the time it takes for your skin to go red or to burn.  Itís really hard to be prescriptive about how long you need because itís different for every person.  Someone whoís very fair like me, I burn really easily.  Iíd probably need much less time in the sun that someone with much darker skin.  Also sun block and sun screen are not perfect: theyíre not this magic shield against the sun.  People donít use them in the way that manufacturers recommend.  They donít put enough on, they donít apply it regularly enough.  Youíll know if your skin burns easily that you can put some on and still get burnt.  Thereís some ultraviolet getting through.  We know there are some studies that show we do need vitamin D to protect us from things like cancer but you can certainly get more than enough vitamin D with casual exposure to the sun: popping to the shops with your sleeves up.  If youíre going to go serious exposure to the sun then definitely protect yourself.


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Sean Moore asked the Naked Scientists: Hey Chris, I love the show. Only a fool couldn't. Does my body still produce vitamin D if I'm wearing sunscreen? Or does this inhibit it? Blue skies, Sean Moore -Winnipeg, Manitoba, Canada What do you think? Sean Moore , Tue, 8th Jul 2008

Hi Sean More,

find the answer in this interesting overview on vitamin D by Prof. Michael Holick:
certain sunscreens stop 99% ultraviolet B radiation, causing 99% drop in vitamin D production by the skin.
I'll find out the slide and data for you, but it will take some time... should work!  

I'm watching it over and improve my english of course!
(Joke, I love this stuff: even helicobacter connections are mentioned)


iko, Tue, 8th Jul 2008

Nice IKO!

Now I have often wondered the same thing especially cause I can't be in the sun without sun block.. I think mine is Factor 70 SPF and usually I use shade.. which is basically a total sun Block! Karen W., Wed, 9th Jul 2008

Well, get your 25(OH)Vitamin D levels checked soon and...
off you go into this new vitamin D ERA!
So far -officially- the best placebo in our brand new millennium.

ikoD    ...on behalf of prof. Holick  (whose video is always there to be watched!) iko, Sat, 12th Jul 2008

Well I found out the hard way.. Iko I just now finished my last dose of vitamin E . They checked me and I am finally caught up enough to stop supplements and she has changed my other meds that prevented me from being unprotected in the sun.. I am now under orders to get at least two 30 minute sessions in the sun a day without sunscreen, if possible.. to help keep my vitamin D up.. I spent 48 weeks of 50,000 units a week, taking it once a week. I can truly say I feel a lot better then I did... which says a lot! Karen W., Sat, 6th Nov 2010

Hi Karen,

It is nice to hear from you...that you feel better!
You could switch to 50.000 units per month, avoiding a sudden 'drop' of this hormone.
Sessions in the sun can't be so effective: too many variables involved.
Take care,

Iko iko, Sun, 7th Nov 2010

Presumably you mean vitamin D.

I think you mean two 30 minutes sesions in the sun a week.

You could do less if you go out in the middle of the day; but it will depend on the time of the year; during the winter, vitamin D production is much slower because UV-B which produces it, is more attenuated at the lower angles in the sky.

For vitamin D production you want your sun at midday- because you can go out for less time and it damages your skin less (because you get less UV-A total dose). wolfekeeper, Sun, 7th Nov 2010

Vitamin D production is caused by UV-B. How much sunscreen blocks UV-B is specifically measured by the SPF factor.

It's more or less an exact ratio SPF-50 blocks all but 1/50th of the UV-B. So if you're out in the sun for an hour, and you have a SPF 15 sunscreen on, then you will produce as much vitamin D as if you had been out for 4 minutes (which would actually be quite a lot, vitamin D production is quite fast). If you had SPF 30 then it would be two minutes.

I think if you're out unprotected (in a bikini or swimming costume) for 10 minutes then your body can make about 10,000 IU. You need about 400 IU per day, and there's very little vitamin D in food (apart from a few like some oily fish like mackerel and salmon.)
wolfekeeper, Sun, 7th Nov 2010

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