I can't find the source anymore, but it's my understanding that north of DC you need to supplement 2000IUs or 50mcg nearly half the year, and north of Mexico du

I can't find the source anymore, but it's my understanding that north of DC you need to supplement 2000IUs or 50mcg nearly half the year, and north of Mexico during Nov-Jan, as the angle of the Earth prevents adequate D production. Not to mention I often don't manage to get 15-30mins of mid-day sun, so I supplement all year round.