4000 IU in summer for a person who is outdoors substantially, or maybe 4000 IU in winter while hibernating?
Latitude or sunny days per year?
;-)
Interesting you mention being outdoor in the sun.
When researching autism I ran across vitamin D as playing a role in its prevention.
This was discovered when Somalis were relocated to Minnesota (won’t go into the wisdom or lack thereof of doing so).
All of a sudden they were having autistic kids. Researchers found the kids had abnormally low vitamin D levels.
Since winter is long and dark, and Somalis have very dark skin, researchers believe that they were not receiving sufficient sunlight.
The Somalis call it the “Minnesota disease”.
North of Miami if one is outdoors for a normal non athletic amount of time then (for me) 5000 units a day and
for indoors only type people, too. If you live in Miami or the Keys and stay outdoors a lot you don’t need it unless it is chilly and you cover up.