Question: 40 mcg = how many iu?
Answer: 500 IU (12.5 mcg) per day increases vitamin D blood levels 5 ng/ml (12.5 nmol/L). 800 IU (20 mcg) per day increases vitamin D blood levels 8 ng/ml (20 nmol/L). 1000 IU (25 mcg) per day increases vitamin D blood levels 10 ng/ml (25 nmol/L). 2000 IU (50 mcg) per day increases vitamin D blood levels 20 ng/ml (50 nmol/L).