I don’t know of any way that is more reliable or less risky. There are more accessible ways (e.g. maximize time outside without burning), but I wouldn’t think of them as reliable, safe or time-efficient.
Determining vitamin D levels will vary by country. You’d have to research how it works.
I’m not aware that healthy people can get too much vitamin D from the sun. In combination with the many beneficial effects of natural light (see melatonin, circadian rhythm, mood, etc.), maximizing time outside without burning seems like the best strategy to me. I just find it easier to avoid getting sunburn with the above calculator. Day-by-day variations are small enough that you might be able to make educated guesses most of the time and not check every time you go outside.
If this collides with one’s life (e.g. work-hours), supplements could be considered, but those come without the other effects of natural light.
Determining vitamin D levels will vary by country. You’d have to research how it works.
I’m not aware that healthy people can get too much vitamin D from the sun. In combination with the many beneficial effects of natural light (see melatonin, circadian rhythm, mood, etc.), maximizing time outside without burning seems like the best strategy to me. I just find it easier to avoid getting sunburn with the above calculator. Day-by-day variations are small enough that you might be able to make educated guesses most of the time and not check every time you go outside.
If this collides with one’s life (e.g. work-hours), supplements could be considered, but those come without the other effects of natural light.
To check the current UV index and ozone column:
https://www.temis.nl/uvradiation/nrt/uvindex.php