Interestingly, Norwegians are tremendously cognizant about keeping their vitamin D levels up:

https://life.spectator.co.uk/articles/on-vitamin-d-sun-starv...

I think another contributing factor is cultural: southern Europeans touch, kiss, and hug each other more than northern Europeans, and may tend to sit and stand a little closer, etc.

Northern Italy is a valley that tends to have very high levels of nitrogen dioxide and other air pollutants [0]. Similarly, Wuhan China has poor air quality, incinerates most its garbage, and recently vaporized a whole lot of pigs (+/- 1million?) due to swine flu.

[0] http://www.esa.int/ESA_Multimedia/Videos/2020/03/Coronavirus...