Vitamin D with an overcast sky

[mommy212]

Does anyone know how long it takes to get your day's worth of vitamin D if the sky is overcast? We are light-skinned and used to just spend 15-20 minutes outside when it was sunny (well, we would spend hours outside when it was nice and warm, but even when it was cold/sunny we could be outside 15-20 minutes) but it will be overcast for the next few months here! Thanks for helping out!

[cameragirl]

From what I understand, you can't make enough vitamin D even with a full day of exposure from Nov. - Mar. if you're north of San Francisco. I'm not sure how much you would actually get, though.