No doubt, but it is an empirical fact that this is not working too well for a nontrivial number of people - and if it were working well, there would still be no

No doubt, but it is an empirical fact that this is not working too well for a nontrivial number of people - and if it were working well, there would still be no reason to bring up the issue in the article about sunbeds, especially as no evidence for vitamin D intoxication being a difficult-to-avoid problem in practice was presented either in that article or above. If sunlight is the optimal solution, then outdoor activity is better for you than lolling on a sunbed. I am a case in point: I am frequently outdoors in all seasons, well beyond the point where I have to be careful to avoid sunburn, yet I have a significant all-seasons vitamin D deficiency. The conclusion of the abstract to the article you link to says "a three-part strategy of increasing food fortification programs with vitamin D, sensible sun exposure recommendations and encouraging ingestion of a vitamin D supplement when needed should be implemented to prevent global vitamin D deficiency and its negative health consequences" [my emphasis.]