There can't be a recommended daily dose for everyone, every body is different. I quote:

"... in a correct analysis of the data used by the Institute of Medicine, it was found that 8895 IU/d was needed for 97.5% of individuals to achieve values ≥50 nmol/L."

That just means there are some people who need a very high dose. For comparison, 4000IU/d gets me well over 50nmol/L, this is also the "generally considered safe" upper limit. There was a case reported on HN where 5000IU/daily caused issues with calcium levels. You gotta get your bloodwork done.