Comment by kenhwang

I'll say track and test yourself, since it depends highly on skin tone and weather.

That study also claims 12-20ng/mL 25-hydroxyvitamin D is sufficient. My doctor says the post-COVID studies suggest 75ng/mL is closer to optimal, and <30ng/mL had been considered deficient for about a decade before COVID.

Personally I had no problem hitting 20ng/mL through sunlight alone and I'm pretty fair skinned but live somewhere sunny. But I haven't been able to get anywhere near 75ng/mL even when I've made an effort to increase vitamin D through supplements and exposure to the sun.