Not that big, but most men have vitamin D deficiency, and that messes up your blood circulation and your PENIS size. Among other more important health stuff.
Vitamin D should always be taking alongside K for safety (or you might fuck your kidneys up).
I took 100 mcg of K2 daily and 50.000 IU of D-3 once every three days, and my erection got 2 cm larger after some weeks, plus I became more of a shower than a grower (not much).
My hair looked better and I felt better, too.

It just goes to show how fucked our health is in general if such a random thing can be improved so easily.