Make in 15-20 minutes in the sun, most of the year this would have to be in the middle of the day, and you can’t have a shirt on. I know so one who gets “his” vitamin D that way, by doing interval running without his shirt on his lunch hour, but some of us would have a hard time with that (especially girls) so we supplement.
You can test how high your D gets in the bloodstream and do some sun, some supplementation. You need it at least 60 especially in winter to fight flus etc. High enough D plus enough sleep, you won’t get sick.
Okay, but just think of all the friends you’d make without the shirt. Just sayin’... LOL
I know what you mean. It may be easier for a guy, but get creative.