> A single, optimal sun exposure session might produce the equivalent of 10,000 to 25,000 IU from a supplement, but it will not keep increasing with more time in the sun. That's your max per session.
"In Scotland, we only get enough of the right kind of sunlight for our bodies to make vitamin D between April and September, mostly between 11am and 3pm."
https://www.nhsinform.scot/healthy-living/food-and-nutrition...
Personally I found that taking Vitamin D supplements made quite a bit of difference - and I spend a fair amount of time outside (~3 hours each day).
We have a saying here to take cod liver oil all months ending with R (in Norwegian that's September to Februar) to get both omega 3 and the vitamin D.
In many countries it is physically impossible to get enough vitamin D from the sun, even if you go out naked.
Also did you ever notice that the cheap apartments in many places are facing north and do not have a balcony, and of course do not have a private garden? Now you are reduced to going to a park which in the "cheap" areas is also not a good spot to chill for 30 minutes.
spoken like someone who has never lived in the UK
For some people even in sunny areas, 5000 IU might be needed to get you in-range. This is highly individual.
It's much cheaper to take a few pills than it is to travel 3000km south to see the sun for 30 minutes :D
We even put Vitamin D in milk by default just so that people would get some extra.
During the spring, summer, fall months I barely need it since I'm outside so much with my dog.
It also sucks a lot when it's dark before starting work, dark after leaving work, and during the day rather cold to be exposing skin to the sun.