> severe VDD was defined as serum 25(OH)D levels of <25 nmol/L, moderate deficiency as 25–50 nmol/L, insufficiency as 50–75 nmol/L, and sufficiency as >75 nmol/L.

These numbers seem high to me. The 75 nmol/L (30ng/L) is not really a reliable value. It was published in a research that raises many questions due to conflict of interests.

Hence the

> ~40% of people don't get enough vitamin D

becomes:

> ~40% of people in the USA don't get enough vitamin D according to Dr. Holick

Where I live the norm is 20 ng/L and if we apply that, then the shocking 40% becomes more reasonable 10-15%