Intro/Key Concepts

    • Vitamin D is crucial and you are probably deficient
    • Blood test is the only way to know – vit D blood levels should likely be in 40-49 ng/mL range
    • MANY Variables determine how much vit D you need
    • Sources of vitamin D – Sun (when UVB is present), safe tanning bed, some food, supplement
    • After sun exposure do not use soap on exposed skin for 48 hours – this may disrupt vitamin D synthesis
    • Supplementing – D3 (cholecalciferol) superior to D2 (ergocalciferol) – 1,000-4,000 IUs considered safe; also supplement w/ Vit K2 (MK-7) to prevent calcification-related health challenges – Vitamin D and K2 – $0.33/day | Vitamin D – $0.13/serving/day | Vitamin K – $0.16/day
  • Supplements are typically required in winter and/or if you don’t get sun exposure
  • Get regular blood tests to stay within optimal range – adjust vitamin D sources accordingly

Why Vitamin D is Important

Vitamin D controls the expression of over 1,000 genes (1/24th of the human genome). Vitamin D is required for proper calcium balance, phosphorous balance, cell differentiation, immune system functioning, insulin secretion, and blood pressure regulation. Deficiencies can lead to rickets in children, osteomalacia (bone softening) in adults, muscle pain, weakness, and increased risk of osteoporosis, diabetes, cancer, and cardiovascular disease. Toxicity (too much vitamin D) can cause heart arrhythmias and weight loss – it can greatly increase calcium absorption and lead to vascular and tissue calcification, causing damage to the heart, blood vessels, and kidneys. More specifically, it can cause kidney stones and even lead to heart attacks and stroke (all that calcium build-up blocks blood flow to the brain and heart).

Adequate Blood Levels (Deficient, Normal, Toxic)

Therefore, it’s super important to get the right amount!!! So, how do we do that? 

That is a question for the ages! It is very controversial.

When you get a blood test for vitamin D, 25-hydroxy vitamin D3 (calcidiol), the major circulating form of vitamin D, which is eventually converted to the active form of vitamin D (1, 25 dihydroxyvtiamin D3) (aka calcitriol) in the kidneys, is what is being tested. This is because calcidiol has a half-life of about 15 days while calcitriol has a half-life of about 15 hours. Calcidiol is a better indicator of actual vitamin D levels.

Serum (Blood) 25-hydroxy vitamin D3 Levels

ng/mL Health Status
<12 DEFICIENT – Leads to Rickets in Infants and Children and Osteomalacia in Adults
12-20 Inadequate for overall bone health
20-49 Adequate for bone health
>50 or 60 Potential Adverse Effects


So, from what I have found, everyone agrees that below 20 ng/mL is bad and above 60 ng/mL is also bad. Emerging evidence is showing that between 40-60 ng/mL is ideal to reduce risk of all-cause mortality (in other words, preventing you from dying from cancer, heart attacks, etc…). Some sources, such as the Vitamin D Council, say that 80-100 ng/mL appear safe although The Institute of Medicine does not feel there is enough evidence suggesting a blood level higher than 50 ng/mL.

Additionally, it makes sense to test the blood levels at the end of summer and the beginning of spring at minimum. This provides a good picture of vitamin D levels at their peak and their lowest point, respectively.

That is controversial enough, but the amount you should be getting in the diet is far more controversial. I’ll explain why in proceeding sections.

Recommended Dietary Allowance

To get blood levels of 25-hydroxy vitamin D to the adequate levels of 20-49 ng/mL, current dietary guidelines given are 600 IUs/day for those between the ages of 1 and 70, 400 IUs/day below the age of 1, and 800 IUs/day for those 70 or older. These guidelines by the Food and Nutrition Board were set only considering vitamin D’s effect on bone health. The guidelines do not necessarily take into account vitamin D’s other important roles in the body.

The Endocrine Practice Guidelines Committee recommends the following:

  • Infants: 400-1,000 IU/day
  • 1-18: 600-1,000 IU/day
  • 18+: 1,500-2,000 IU/day
  • BMI >30: 2-3x more
    • This means if you have a BMI over 30 it is recommended to take 2 to 3 times more the values listed

The Nutrition Source (Harvard) recommends:

  • 1000-2000 IU/day and up to 4,000 IU/day if effective UV exposure is limited.

The Linus Pauling Institute (Oregon State) recommends:

  • 2000 IU/day for adults.

The Vitamin D Council has very specific recommendations based on your current vitamin D blood test results and by how much you wish to raise your vitamin D levels. You can view those here: What Do my Vitamin D Results Mean?.

The American Academy of Pediatrics recommends 400IU/day supplement for breast-fed infants as vitamin D is minimally transferred through breast milk.


Our body has the amazing ability to convert UVB radiation from sunlight to the vitamin D required by the body. So, in theory, when sun exposure is adequate, and we expose our skin to the sun, we can get all the vitamin D our body requires! And, we don’t risk overdosing – vitamin D toxicity is associated with supplementation, not sun exposure (although excessive sun exposure can cause sunburn which isn’t good.)

One study showed that the amount of sunlight required to produce a slight pinkness of the skin was equivalent to ingesting 10,000-25,000 IUs of vitamin D from food. Holy salmon! And the general guideline is that 5-15 minutes of sun exposure between 10 AM and 3 PM in spring, summer, and fall months provide adequate vitamin D.

But, it is important to note that UVB radiation does not penetrate the atmosphere and therefore does not reach our skin at certain latitudes during many months of the year. If UVB radiation is not present, we cannot use it to convert the 7-dehydroxycholesterol in our skin to vitamin D. For instance, in my hometown of sunny Fort Lauderdale, FL, UVB is present between Feb 12-Oct 28, so there are only three months in which I could not get vitamin D from sun exposure. Where I currently live, Portland, OR, it is only possible to get vitamin D from sun exposure between April 4 and September 7. So, in theory, for five months of the year, I have to figure out another way to get vitamin D. I determined this here: If the sun is above 50 degrees from the horizon, UVB penetrates the atmosphere.

There are electronic ballast tanning beds designed to emit a 10:1 ratio of UVA to UVB. These tanning beds, in theory, are a safe source of the UVB needed to synthesize vitamin D. They are not the magnetic ballast tanning beds typically found in a tanning spa. They are quiet as opposed to being very loud. From my understanding there is not a ton of research regarding using tanning beds for the specific purpose of synthesizing vitamin D in the body. Dr. Mercola was actually fined millions of dollars by the FTC for selling devices and forced to refund the customers who purchased the beds from him. So, it is difficult to promote these tanning beds, although the theory behind using artificial UVB for this purpose seems valid.

Although this is all true, it is very interesting (and counterintuitive) to note that a major analysis pooling nearly 400 studies concluded that there was no effect of latitude on 25-hydroxy vitamin D levels, disproving the notion of the “Vitamin D winter.”

With skin exposure, there are some other important factors to consider when using it as your primary source of vitamin D. They are:

  • Age – The elderly have a reduced capacity to synthesize vitamin D in skin from UVB exposure
  • Skin Pigmentation – The darker you are, the more difficult it will be to synthesize vitamin D in skin form UVB exposure
  • Use of Sunscreen and SPF Clothing – These will block UVB
  • Body Fat – The more fat you have, the more vitamin D is being stored in your adipose (fat) tissue, making it less available in the blood stream – therefore you would need more vitamin D in theory to sustain adequate levels
  • Genetics – Certain individuals have gene polymorphisms (specifically CYP2R1 gene mutation) which influence the ability to synthesize vitamin D in skin form UVB exposure
  • Current Conditions – Amount of UVB is affected by other factors such as time of day, length of day, season, smog, and cloud coverage


Food is another source of vitamin D, although not many foods contain it. Here is a list of foods that do:

  • Cod Liver Oil – 1,360 IU/serving
  • Salmon (Sockeye) 3 oz – 447 IU
  • Fortified Foods (Milk, Orange Juice) – 115-137 IU/serving
  • Sardines (2) – 46 IU
  • Beef Liver (3 oz) – 42 IU
  • Egg (1 Large from yolk) – 41 IU
  • Fortified Cereal – 40 IU
  • Cheese – 6 IU
  • Mushrooms (Sun-Exposed) – Amount varies and is in form of vitamin D2 (ergocalciferol)

For more foods I don’t necessarily recommend eating that also contain vitamin D (like swordfish):


Vitamin D Supplements come in two forms – vitamin D3 and vitamin D2. Although controversial, many studies are suggesting that vitamin D3 is more effective at raising serum 25-hydroxy vitamin D levels than D2 and therefore a superior supplement.

Vitamin D3 is traditionally derived from lanolin, which is a wax secreted from wool-bearing animals (i.e. sheep). There is a lichen-derived source of vitamin D3 available as well. Lichen-derived is a vegan-friendly source of vitamin D3.

It is important to note the potential for toxicity when supplementing with vitamin D3. Generally, supplementing with 1,000-4,000 IUs is considered safe. Toxicity is associated more with 100,000 IUs or more for weeks or months. Under the direction of a physician, high doses of vitamin D may be initially given to correct a deficiency and then a maintenance dose given to sustain desirable blood levels of vitamin D. Therefore, toxicity is also dependent on the amount of vitamin D initially in the bloodstream before testing.

When you have adequate levels of vitamin D, your ability to absorb dietary calcium increases between 20 and 30 percent. Remember what you read earlier about excessive calcium causing potential health conditions. The way to address this is to supplement with vitamin K (specifically vitamin K2 MK-7 natto derived). I won’t get into all that here, just go to vitamin K via the search bar to learn more. Essentially, vitamin K activates proteins which shuttle calcium out of the bloodstream and into the bones and tissues. So, you don’t get a build-up and you have strong bones and tissues!

It’s also important to note that vitamin D is a fat soluble vitamin and requires dietary fat intake for proper absorption. It should therefore be taken with a meal containing fat. There are also vitamin D supplements with carrier oils such as extra virgin olive oil.


Vitamin D is complicated. What we saw is that having a blood level between 40-49 ng/mL is considered ideal by multiple parties, although some suggest 40-60 ng/mL is ideal. Getting within this range is dependent on so many different variables that it is virtually impossible to provide a “one size fits all” recommendation. Here is the simplest thing to do: get a blood test! A blood test will show you your exact level. You can tweak your intake from there. And then, continue doing follow up blood tests every few months, and at minimum, a blood test at the end of summer and beginning of spring. Again, with all the variables, you will likely need to supplement in the winter but may be perfectly fine without supplementing in the summer. In fact, you may drive vitamin D levels into the toxic range if you consider supplementing in the summer at the same dose you were in the winter. The best way to get vitamin D appears to be via sunlight exposure (when UVB is present). Because the body can synthesize such a large amount from such little exposure, it is prudent to not overdo it. You’ll have the vitamin D without the sunburn.

I hope you found this helpful! If you have any questions or comments, feel free to get in touch!



References/Additional Resources

  11. – D3 v. D2
  12. – Influence of latitude on 25(OH)D
  20. – Personalizing Nutrition Based on Genetics – Rhonda Patrick
  21. Understanding Vitamin D Video

Facebook Comments