Hi Rosie,
Please be assured, I don't have a beef with you — it's the choice of words in the original research article title that sticks in my craw. What you are saying is quite correct. It appears to fall under scenario number 4 in my post above.
Sure, I'll grant you that people who work as roofers and other jobs that normally provide long hours of sun exposure, can still get more-than-enough vitamin D from the sun, whether they use sunscreen or not. But then most roofers probably rarely use sunscreen. The problem I have with this research article is that (as is so often the case) it's poorly-written and because of that it's misinterpreted by most people so that by the time the research trickles down to the general public, the general impression is very misleading. It leads readers to infer that they can still get plenty of vitamin D from the sun even if they use sunscreen. That's simply not true for the majority of people. If it were true, there wouldn't be a world-wide epidemic of vitamin D deficiency.
Look at the title of the original article:
Optimal sunscreen use, during a sun‐holiday with a very high UV index, allows vitamin D synthesis without sunburn
That's correct because apparently a reduced level of vitamin D synthesis does get through the sunscreen. The problem is, it's a half-truth because the title doesn't acknowledge that this is a reduced level (and you and I both know that it is). So when Science Daily interpreted the article, their title was:
Does sunscreen compromise vitamin D levels? Maybe not
I believe you'll agree that this seems to imply that the pass-through synthesis of vitamin D is not necessarily limited by sunscreen. Because even though you're a trained scientist, you used this title:
Sunscreen doesn't interfere with Vitamin D synthesis
See what I mean? That removes all doubt about any limiting factor. The original title was a half-truth, and this was misinterpreted at every step down the line until the final verdict appears to be that sunscreen does not limit vitamin D synthesis (at all).
My point is, if you're going to use sunscreen, you're going to require significantly more sun exposure than you would if you were not using it, if you intend to achieve the same level of vitamin D synthesis from sun exposure.
Tex (who's never used sunscreen in his life, and who has to take vitamin D supplements in order to maintain a decent vitamin D level, even though he's lived and worked on a farm in sunny Central Texas all his life).
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Why didn't they include a comparison with a control group who absorbed a similar amount of sun — without the sunscreen? Because it would have dwarfed their results, and exposed their slight of hand trick. When one considers that the average vitamin D boost with an equivalent sun exposure (without sunscreen) normally runs in the thousands or tens of thousands of IUs, I have to view this research conclusion with the same jaundiced eye as my grandfather would have viewed a horse trader back in his day.
