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.
* 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.
