It's not just vitamin D, it's a long chain of different reactions. I prefer to run topless always if temps are comfortably above +5 Celsius. Unfortunately, Euro

It's not just vitamin D, it's a long chain of different reactions. I prefer to run topless always if temps are comfortably above +5 Celsius. Unfortunately, Europe is probably the darkest place on earth at least in winter months, but this is the place where especially light skinned people evolved. Sun exposure without sunlight is of course not very efficient, but it's worth to use those rare moments when it shines.