I spend a fair percentage of my recreation time outside in California and as far as I can tell, if you work indoors and wear sunscreen outdoors it's probably hard to get enough vitamin D from the sun, anywhere.

And this article is about Finland. Seattle is 47N LAT, Helsinki is 60N. That's around how far north Whitehorse is in the Yukon - very little Vitamin D is possible from sun exposure that far north.

Yep, around here it's mostly the early afternoon hours during summer months that the UV levels even rise above the threshold of triggering cholecalciferol synthesis. For many people the summer vacation is pretty much the only time of the year that they have a chance to synthetize vitamin D on their own.

Contrary to that, I've read that in the south of Britain, so say 51°N, just 15 minutes exposure in the middle of the day in the spring and summer months, on the face and hands alone, gives you sufficient vitamin D for the whole year.

* "Sufficient" ≠ Optimal

* That's for light skinned folks.

* I suspect the difference between 51°N and 56°N (ie, Scotland) in such a study would be much larger than most would think.

* From the authors: "It is important to note that this should be undertaken in the middle of the day, with exposure of lower arms and lower legs to maximise benefit."

Sufficient is enough, and yes I am aware that the difference at the other end of the country is indeed stark, the point being that southern Britain is still several degrees north of the parent post's Pacific Northwest, where it was said to be impossible.

I'm at 47°N and anecdotally, I did ~30-40 minutes walks in the midday sun this summer, with either face/hands/arms or additionally also legs exposed. At the end of summer I measured at 26mcg/l, which is barely above the "deficient" threshold of 20mcg/l and still well below the often recommended target of 50mcg/l. So I doubt that "face and hands alone" will give you "sufficient vitamin D for the whole year". Note that I was also taking 2000 IU per day in winter/spring, which I stopped taking in summer. Now after the bloodtest I've resumed the supplement for fall and upped it to 4000 IU + added Vitamin K2.

Fun fact for anyone who’s never been this far north:

I grew up In Edmonton Alberta, and in the winter not only is there not much benefit from sun exposure, but: the sun does not warm you. The sun feels cold even at full-bright noon.

Feb 17 -> Oct 22 you can get vitamin D from the sun in the PNW, although for a chunk of that its not going to be enough to get you to 8000 IU.