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The amount we need to take is best arrived at by a blood test. I take a 5,000 IU vitamin D gelcap every other day, and with my multivitamin I am getting 3,100 IU a day. This makes my vitamin D blood test come back at 34 ng/mL, which is 85 nmols/L.

In the US, we primarily use “ng/mL.” while most countries use “nmols/L.” The conversion factor is 2.5X ng/mL = nmols/L.

It is important to get these straight. Why?

56ng/mL = 42% higher risk of death:

https://pubmed.ncbi.nlm.nih.gov/22573406/

46 ng/mL = 24% increase in cancer deaths:

https://pubmed.ncbi.nlm.nih.gov/35026158/

36+ ng/mL = 13% increase in heart attack and total death rate:

https://www.ncbi.nlm.nih.gov/pubmed/23533239

4,000+ IUs a day decreases bone density by at least 3.8% in women (blood at 53+ ng/mL):

https://jamanetwork.com/journals/jama/article-abstract/2748796
https://asbmr.onlinelibrary.wiley.com/doi/abs/10.1002/jbmr.4152

People double the times they fall at higher rates of vitamin D intake:

https://jamanetwork.com/journals/jamainternalmedicine/fullarticle/2478897

So, we need to make sure we and our doctors are properly noting the actual measurement units from our blood tests and not seek huge amounts of vitamin D, if we don't need them.

There are problems with too much vitamin D.

A handy vitamin D unit conversion calculator:

http://www.endmemo.com/medical/unitconvert/Vitamin__D.php