Science Questions

You have to spend 10-20 minutes in the sun to make vitamin D. Since I moved to Australia I’ve 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? Alan, Sydney; Sean Maul, Canada

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.  It’s also the stuff that damages your skin and gives you skin cancer.  This is why in somewhere hot and sunny like Australia it’s very highly recommended you protect yourself in that way.  You do only need a few minutes of sun exposure to make enough vitamin D.  It’s certainly less than the time it takes for your skin to go red or to burn.  It’s really hard to be prescriptive about how long you need because it’s different for every person.  Someone who’s very fair like me, I burn really easily.  I’d probably need much less time in the sun that someone with much darker skin.  Also sun block and sun screen are not perfect: they’re not this magic shield against the sun.  People don’t use them in the way that manufacturers recommend.  They don’t put enough on, they don’t apply it regularly enough.  You’ll know if your skin burns easily that you can put some on and still get burnt.  There’s 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 you’re going to go serious exposure to the sun then definitely protect yourself.

September 2008