This is all relative. In my world, this isn't such a large dose. It's above the 'normal' but not exceptionally large in the view of many Drs who are very knowledgeable in the broad dynamics of Vit D3. We still refer to VitD as 'vitamin' but it functions more similarly to a hormone, according to many. It's essential for many functions. My biology has high elements of allergy- aka immune response dysfunction. I also carry a cancer genetic mutation gene. I also had 2 COVID-19 viruses. Vitamin D has relationship to the prevention+ healing processes in these, and other biological specifics that makes 'me'. I'm healthiest when my levels are within the range that my Dr uses for 'normal.' There's much about VitD3 now in mainstream medical literature today. Even the top medical academic institutions we respect most will state they only *extreme* amounts of VitD taken over a very long time will cause problems. Don't take my word for this, look it up for yourself. I find medical care that is comprehensive + includes state of the art disease prevention. Prevention most often is outside of the realm of medical pharmacology. It falls within the realms of lifestyle, nutrition, mental health etc. Those Providers have different parameters for things like nutrition+ supplementation. They don't use the US Govt (low) min standards for daily intake. My last provider who was a nightmare for me, was overweight, emotionally toxic + eruptive. He knew nothing at all about nutrition or supplements + never mentioned it. And cared to learn nothing. Everything for him was pharmacology, referral to experts etc. He viewed everything within the medical disease model. My current provider (Thank you God) is academically educated in the health model and lives it herself. I'm finally recovering after 1 1/2 years of long COVID when I had little progress w her comprehensive help.
I have an advantage some others don't in that I have a medical background with continuing education for my own interest. I have a basis that enables self determination more than some people do for self-directed health care. Tho I have a heavy family history of common chronic illnesses + a genetic predisposition to another, I've managed to reach Senior age with none. I attribute this to God's Grace and the health decisions I've made over the entire course of my lifetime. To summarize, I take 10k IUs of Vit D3 bc the range of 5k-10k ius is what the experts that I follow believe is the target range for health maintenance. Since I have predispositions + risk, I go to the higher range.
I hope this sheds some light on why.
So nice to have dialog with you. Be blessed.