Interesting, I used to watch his videos during the pandemic.  He takes a very high level of Vitamin D3 every day.   The NHS say a limit of 4000 IU is recommended.   The study says every 800 IU you take reduces your chance of death by 9% for PCa sufferers and all causes.
I've been taking a supplement of about 500 IU every day this year so we'll see how it goes.  I might increase it to 1000.
It's confusing that there are 3 ways of measuring Vitamin D3 quantity and that it's Vitamin D3 not just Vitamin D.  The IU or International Unit seems the least confusing.  It's easy to confuse 20 nmol/L with 20 microG/ml.
I'm not sure about the claim D3 can reduce Gleason in the other study.
Another doctor on YouTube is saying increasing your heart rate through exercise for 150 minutes a week also slows progression although it's based on a lab test of PCa cells.