Short answer: my personal experiment showed that four months of 5,000 IU/day vitamin D3 changed my measured 25-hydroxyvitamin D from about 33 to 38 ng/mL. That is interesting as an N=1 observation, but it does not establish that 10,000 IU/day is safe, necessary or beneficial for other people.
The previous version of this article made exactly that leap. I wrote that 10,000 IU/day “may indeed be feasible, safe and potentially beneficial.” I no longer think my data support that conclusion.
What my experiment actually tells us
A person’s response to vitamin D supplementation depends on baseline status, body size, absorption, sun exposure, assay variation, genetics, adherence and other factors. My small increase while taking 5,000 IU/day mainly tells us how my measured level behaved during that period.
It cannot establish a population dose-response curve, toxicity threshold or ideal target concentration.
What current reference values say
The NIH Office of Dietary Supplements summarizes the National Academies’ tolerable upper intake level for adults as 4,000 IU (100 micrograms) per day. The same fact sheet notes that vitamin D toxicity can cause hypercalcemia, hypercalciuria, kidney injury, soft-tissue calcification and cardiac arrhythmias.
The NIH also notes that 25(OH)D concentrations above about 50 ng/mL can be associated with adverse effects, while the optimal concentration for general health has not been firmly established.
Does that mean doses above 4,000 IU are never used?
No. A clinician may prescribe higher doses for a documented deficiency or a specific medical situation, often for a defined period and with appropriate monitoring. A tolerable upper intake level is not the same thing as a poisoning threshold. It is a population safety boundary for chronic intake without medical supervision.
The 2024 Endocrine Society guideline changed the tone
For generally healthy adults younger than 50, the Endocrine Society suggests against routine empiric vitamin D supplementation above the established dietary reference intake and against routine 25(OH)D testing. The guideline also emphasizes that outcome-specific “optimal” blood thresholds have not been established for healthy people.
Bottom line
I still think the original experiment is worth publishing because real repeated measurements are useful. The corrected conclusion is narrower: 5,000 IU/day produced only a modest rise in my 25(OH)D during this period. It does not justify recommending 10,000 IU/day to readers. Higher-dose vitamin D is a medical dosing question, not a conclusion that can be drawn from one person’s laboratory results.
Sources
- NIH Office of Dietary Supplements: Vitamin D Fact Sheet for Health Professionals.
- Endocrine Society 2024 Clinical Practice Guideline: Vitamin D for the Prevention of Disease.
Medical information
This article may contain published medical evidence, clinical context, personal observations, or hypotheses. These are not equivalent levels of evidence. See the Editorial & Medical Review Policy and Medical Disclaimer. This content is educational and does not provide an individual diagnosis or treatment plan.
July 2023 update: when it started getting sunny, I stopped taking Vitamin D3 two months ago. I wanted to see how much the sun could increase its amount in my blood. After going to Majorca, my level was 54 ng/ml, up from 38 ng/ml in early June. So, it looks like sun helps more than even taking 10,000 IU of Vitamin D a day.