> 5000 IU/day

Ironically these "IU/day" estimates are bogus. Direct ~noon sunlight at the equator for fair skinned individuals produces (full body exposure) 15-50k IU/hour of D3 equivalent, depending on the estimate. You clearly don't see people dropping dead after two hours in the sun.

GPT response For a fair-skinned adult, nude or essentially whole-body exposed, at solar noon near the equator under a clear sky, a reasonable order-of-magnitude estimate is:

Exposure Approx. D3-equivalent produced ~3 min ~2,500–6,000 IU ~5 min ~4,000–10,000 IU ~10 min ~8,000–20,000 IU ~10–15 min / ~1 MED ~10,000–25,000 IU >20–30 min does not keep increasing linearly

The best-known experimental anchor is that roughly one full-body minimal erythema dose (1 MED)—enough UV to cause faint redness later—is associated with a vitamin-D effect comparable to ingesting about 10,000–25,000 IU (250–625 µg) of vitamin D3. Reviews note that this estimate has also received support from outdoor solar-exposure studies, although the original experiments used artificial UV sources. https://pmc.ncbi.nlm.nih.gov/articles/PMC3257661/ study