https://pmc.ncbi.nlm.nih.gov/articles/PMC4210929/

The reanalysis paper suggests that, to get about 97.5% of people to at least 20 ng/mL (50 nmol/L), an intake around 8,900 IU/day would be needed, which is far above current official recommendations. However, major medical bodies still advise much lower routine doses and treat such high intakes as above the usual safe upper limit.[1][2][3][4][5]

What the reanalysis suggests

• Using the same data the Institute of Medicine used, the statisticians estimated that about 8,895 IU/day would be required so that 97.5% of individuals reach at least 50 nmol/L (20 ng/mL).[3][1]
• This is roughly 10–15 times higher than the current RDA of 600 IU/day for most adults, which they argue is the result of a statistical miscalculation.[4][1]

What official bodies recommend

• The Institute of Medicine (now the National Academies) RDA is 600 IU/day for adults up to 70 and 800 IU/day for those over 70, with a tolerable upper intake level of 4,000 IU/day.[4]
• The Endocrine Society suggests that many adults may need 1,500–2,000 IU/day to keep blood levels consistently above about 30 ng/mL (75 nmol/L), which they consider a preferable minimum.[2][5]

Practical takeaways

• The “8,900 IU” figure is an argument that the true RDA (to cover almost everyone) is much higher than current guidelines, not a blanket dose recommendation for individuals.[1][3]
• In practice, most mainstream advice lands around 1,000–2,000 IU/day as a generally safe supplement dose for adults, with higher doses reserved for people monitored by a clinician who is checking blood 25‑OH vitamin D levels and other risk factors.[6][5]

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