Medical organizations, including the National Academy of Medicine in the US, the Endocrine Society, and others have developed recommendations for both the recommended daily intake of Vitamin D, as well as ideal levels to have circulating in the blood [1-10]. An important caveat to these recommendations is that they assume zero Vitamin D synthesis from the sun. Since the sun is historically the main way that humans have obtained Vitamin D  (with the exception of Arctic peoples ), it doesn’t really make a lot of sense to think of Vitamin D requirements in terms of intake through food or supplements. Nevertheless, experts have made some recommendations concerning Vitamin D uptake and Vitamin D levels in the blood.
There are a few different ways in which recommended Vitamin D levels are shown, which can get confusing. Some recommendations are shown in terms of target blood concentrations, whereas others are expressed in term of how much should be taken in supplements. Additionally, blood Vitamin D levels can be shown as ng/liter or nmol/liter, whereas recommended dosages for intake can be shown as nanograms (ng) micrograms (mcg), International Units (IU), or a percentage of recommended Daily Allowance (% RDA; RDA generated by National Academy of Medicine). Here are some tables to help you make sense of all these numbers. As you can see, experts mostly agree on ideal levels of Vitamin D in the blood, but disagree on how much Vitamin D supplementation is needed to achieve those levels. This disagreement is perhaps not too surprising considering that most of our Vitamin D comes from the sun’s action on our skin, and not from food.
- dark skin (blocks UV-B rays needed for Vitamin D synthesis in deeper skin layers [more info])
- lack of sun exposure (eg during winter)
- increased age (changes in the skin and kidney reduce the ability of the body to manufacture Vitamin D from the sun, although intake from food/supplementation is unaffected [7,13,14])
- pregnancy (healthy fetal development requires substantial Vitamin D, and will deplete maternal supplies [7,15,16])
- obesity (because Vitamin D is fat-soluble, it becomes sequestered in fat and unavailable in blood for cells that need it [7,17-20])
|Source of Recommendation||Target Blood Concentration
|Target Blood Concentration
|National Academy of Medicine [5,6]||30-60 ng/liter||50-125 nmol/liter|
|Endocrine Society [7,8]||30-60 ng/liter||75-150 nmol/liter|
note: 1 ng = 2.5 nmol (for Vitamin D3)
|Source of Recomendation||Recommended Daily Intake
|Recommended Daily Intake
|National Academy of Medicine [5,6]|
|0-12 months||400 IU||10 mcg|
|1-70 years||600 IU||15 mcg|
|over 70 years||800 IU||20 mcg|
|Endocrine Society [7,8]|
|0-12 months||400-1000 IU||10-25 mcg|
|1-18 years||600-1000 IU||15-25 mcg|
|over 19 years||1500-2000 IU||38-50 mcg|
|obese children, adults||double the recommendation|
1 mcg = 1000 ng
1 mcg = 40 IU (for Vitamin D3)
1 IU = 25 ng (for Vitamin D3)
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