Thank you for your valuable feedback Frank. The recommend dose change based on ages and health conditions. I provided all those details in this article https://medium.com/sensible-biohacking-transhumanism/vitamin-d-as-a-steroid-hormone-not-just-another-supplement-495a2f55c984

In addition to regular sun exposure, I use 5,000 IU for over a decade to keep my D levels at optimal. I regularly get my levels checked. This amount works for me. A few friends use 10,00 IU as they are concerned about sunlight in Australia. In downunder we don't have these high doses yet. The common does are 1000 and 500 IU. I order mine online from the US, a certified company that I trust.