If you eat meat there is never a reason to supplement. The only reason they used COD Liver oil is because they made salted fish or worse Lutefisk and they needed to keep the D in the Oil..
Keep in mind this was for a cured, dried, lye preserved winter diet only...
I'll stick with the few minutes of sun is enough no matter where as long as the receptors aren't plugged but only because I know how to pick my fights...LOL