[tomatsu]

4,000 IU per day is the recommended supplement limit.

You can synthesize 1000 IU from 10 minutes in the sun if... you're young, have light skin (of which most is visible), don't wear sunscreen, it's the middle of the day & summer, and you're lying down to get roasted.

4,000 IU is equivalent to getting burnt to a crisp.

[YokoZar]

This is off by a factor of 10. You get between 10,000 and 25,000 IU in just a little under the time your skin takes to burn. https://www.vitamindcouncil.org/about-vitamin-d/how-do-i-get...

You are very unlikely to develop excess vitamin D unless you supplement more than 10,000 per day for months, and typically not even then unless you exceed 40,000 per day via supplements. https://www.vitamindcouncil.org/about-vitamin-d/am-i-getting...

Additionally, if you supplement or take K2 with vitamin D, the risks are substantially mitigated (Vitamin D adds calcium ions to things, K2 takes them out).