The exception makes the rule; D is the one vitamin I'm aware of whose primary source was never food. Thus, it would not be shocking if food sources were a chal

The exception makes the rule; D is the one vitamin I'm aware of whose primary source was never food. Thus, it would not be shocking if food sources were a challenge. An interesting question though- how many IU do you take? What's your absorption rate, and what's the absorption rate from e.g. salmon? I recall hearing, frequently 10% or less of the D in supplement form is actually absorbed.