None of these guarantee low vitamin D, and none of them rule it out. They're the groups that established research consistently finds testing lower on average — worth knowing if you recognise yourself in more than one.
Full working days spent inside, away from direct sun.
Both limit how much UVB actually reaches the skin.
Skin becomes less efficient at synthesising vitamin D with age.
Vitamin D can be held in fat tissue rather than circulating in the blood.
Kenyan hospital data links lower vitamin D with poorer blood sugar control.
Conditions like Crohn's or coeliac disease can limit how well the body absorbs a fat-soluble vitamin like D.