[HugeAcumen]

* "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."

[hanoz]

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.