Because for a lot of people just 15-20 minutes a day with bare arms and face is more than enough sunlight. Also the body stores vitamin D in fat cells as well,

Because for a lot of people just 15-20 minutes a day with bare arms and face is more than enough sunlight. Also the body stores vitamin D in fat cells as well, it's not like vitamin C that goes through you pretty quickly. On those nice sunny days you can build up your stores so to speak if you're out for a long time. However I can name plenty days I never even go outside during the sunlight. I prefer evening and night activities. I do take a supplement as a result of my doctor finding I had low vit-d level, now I take a 2000IU supplement every day.