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Information on the latest vitamin D news and research.

Find out more information on deficiency, supplementation, sun exposure, and how vitamin D relates to your health.

How do we know how much vitamin D you make?

It’s often stated that the human body can make 10,000 to 25,000 IU of vitamin D, maybe more, in a single session of full body sun exposure. This might make you wonder, how do we know that?

As many know, we measure your vitamin D “stores” by measuring 25(OH)D in your blood. When you input vitamin D, it gets sent to your liver to turn it into 25(OH)D, so the rest of your body can put it to use.

What many don’t know, is that you can actually measure serum vitamin D in the blood, essentially a measure of vitamin D before the liver has converted it to 25(OH)D. After a good day’s worth of sun exposure (or sunbed) or after a large oral dose of vitamin D, you’d expect serum vitamin D to spike briefly, as the body needs some time to transport this serum vitamin D to the liver and start metabolizing the vitamin D into 25(OH)D.

Thus, we can start to compare, how much serum vitamin D is in your blood immediately after sun exposure and how much serum vitamin D is in your blood immediately after you take a certain amount of supplement?

Before we take a look at the research, remember that we measure UVB doses in units of J/m². For skin type II (white skin, usually burns), a dose of 200 J/m² will produce a slight pinkness to the skin. So to give you some orientation before we talk about other doses, remember that 200 J/m² is about equal to 15 to 30 minutes of solar noon sun exposure in the summer.

Now, let’s start by looking at some UVB studies and how much serum vitamin D was made when subjects were exposed to lamps:

  • In a study in 1982, Professor Thomas Clemens and colleagues exposed two people with skin type III to full body UV at a dose of 540 J/m². They found that after 1-2 days, the participants’ serum vitamin D rose to peaks of 61 ng/ml and 44 ng/ml. Note that this is a sun-burning dose of UV exposure, which explains the very high serum vitamin D levels.
  • In a study in 1989, Professor Lois Y Matsuoka and colleagues exposed 32 participants to UVB doses incrementing from 30-300 J/m². They found that participants who received a dose of 300 J/m² had peak serum vitamin D levels of just over 15 ng/ml after about 24 hours.
  • In a study in 1993, Professor John G Haddad and colleagues exposed 10 healthy adults to a UV dose of 270 J/m². They found that participants had peak serum vitamin D levels of 9 ng/ml.

Now, let’s look at the studies that look at some supplementation studies and how much serum vitamin D was found:

  • In 2003, Professor Vin Tangpricha and colleagues administered 25,000 IU of vitamin D2 in either milk or oil and routinely measured serum vitamin D levels over the next 72 hours. Serum levels rose to a peak of 29.6 ng/ml after 12 hours.
  • In 2005, Professor Vikram Mistry and colleagues administered cheese fortified with vitamin D2. They found that per 10,000 IU of vitamin D2, peak serum vitamin D levels rose to 15 ng/ml.

When researchers gather all this data, they can start to reasonably estimate and project how much vitamin D you make from sun exposure based on the subsequent serum vitamin D levels. When we subject ourselves to full body sun exposure, enough to induce a slight pinkness, we probably make between 10,000 to 25,000 IU of vitamin D.

If we put this concept into a graph, it would look something like this:

serum vitamin d

As shown in the Clemens et al study in 1982, the human body can make even more when getting enough sun exposure to get a sunburn. After a dose of 540 J/ m² (about equivalent to an hour and a half of intense sun exposure), one participant with fair skin achieved serum vitamin D levels of 61 ng/ml, more than double what an oral intake of 25,000 IU achieved (29.6 ng/ml). Given this, it’s not unreasonable to extrapolate that the human body can make up to 50,000 IU of vitamin D after a day of burn-inducing sun exposure.

Please note that this does not give justification to supplement daily with intakes in this range. If you got daily sun exposure over a long period of time, your skin would usually develop a tan, shielding the skin from much UVB and slowly decreasing the amount of vitamin D you could make per day. For this reason, it appears that oral intake of 5,000 IU/day is about equal to what your body is capable of making with year-round sun exposure, though every person’s requirements vary a little.


  1. Clemens TL, et al. Increased skin pigment reduces the capacity of skin to synthesise vitamin D3. Lancet. 1982.
  2. Matsuoka LY et al. In vivo threshold for cutaneous synthesis of vitamin D3. J of Lab & Clin Medicine, 1989.
  3. Haddad JG et al. Human Plasma Transport of Vitamin D after Its Endogenous Synthesis. J. Clin. Invest., 1993.
  4. Tangpricha V et al. Fortification of orange juice with vitamin D: a novel approach for enhancing vitamin D nutritional health. J of Clin Nutrition, 2003.
  5. Johnson JL et al. Bioavailability of Vitamin D from Fortified Process Cheese and Effects on Vitamin D Status in the Elderly. J. Dairy Sci., 2005.

  About: Brant Cebulla

Brant Cebulla was a staff member for the Vitamin D Council from May 2011 to April 2014. He has keen interests in nutrition and exercise.
This entry was posted in Blog. Bookmark the permalink.

13 Responses to How do we know how much vitamin D you make?

  1. Rita and Misty says:

    Nice article, Brant. :)

    It’s certainly true that If you get daily sun exposure over a long period of time, your skin would usually develop a tan, shielding the skin from much UVB and slowly decreasing the amount of vitamin D you could make per day….

    What I find fascinating is my personal experience of simply not burning with sun exposure anymore, since my 25(OH)D level has reached optimal. I know others here have commented similarly. BTW–I am skin level 2, which is light…

    I always wonder about this phenomena…

    Be well,

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  2. I too have found no sunburns with vitamin D level > 50 nanogram
    Was bicycling in the hot noonday sun for 2 hours last week, on a road such just the left leg got hot from the sun. No sunburn or even a color difference the next day.
    This has been mentioned by by many individuals, but I have not seen any study (yet)

    Note:The studies mentioned above were with Vitamin D2, not D3
    – So the D3 IUs should be about 30% less.to get the same nanogram increase
    – that is, 7,000 IU of D3 = about 10,000 IU of D2
    See Overview D3 better than D2: http://is.gd/vitd3d2

    Note: The studies mentioned above (probably) used a combination of UVA+UVB.
    – There are many indications that UVB without UVA will create even more vitamin D

    An Overview of UV and Vitamin D, http://is.gd/UV_VitD, highlights the knowns and the controversies, and has hyperlinks to 200 other reports on noonday sun, UV and vitamin D

    Note that the nanogram response to UV or Vitamin D varies by 6X depending on current vitamin D blood levels. http://is.gd/doseresponse

    Note that there is a 4X difference between individual responses to the same amount of supplement (or UV?) http://is.gd/doseresponse

    Note that there is about a 3X less vitamin D generated by elderly skin to the same amount of UV.

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    • Brant Cebulla says:

      Henry, I could be wrong, but I don’t believe there is evidence that absorption of D2 versus D3 is any different. Absorption vs metabolism vs preferential treatment are three separate things. The referenced studies in this blog only look at absorption, not metabolism or use of. So there isn’t good reason to believe that these serum vitamin D [not 25(OH)D] wouldn’t also reflect the absorption of D3.


  3. Does anyone know the source of
    ”It’s really a matter of getting 10 minutes of sun exposure of the arms and face in summer”
    I have so far tracked it back to the early 1980’s where it was in reference to getting 400 or perhaps 1000 IU of vitamin D. Have not found the source yet.

    Yes, 10 minutes would be enough IF
    you are near the equator
    AND young
    AND not obese
    AND have light skin
    AND it is summer
    AND it is the middle of the day
    AND you have lots of skin exposed to the sun (not just arms and face)
    AND you are lying down
    http://www.is.gd/timeinsun has details

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  4. mslarma says:

    Hi. Just wondering if anyone could tell me the optimal dose of Vitamin D for a newly diagnosed case of Bowel Cancer and for someone who has second bone cancer (primary is breast cancer). Much appreciated.
    thank you.

    ms larma

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  5. Rita and Misty says:

    Dear MS Larma,

    I am sorry to hear of your health situation. My thoughts are with you, and I am sending good karma your way.

    You ask excellent questions.

    Unfortunately, here in the United States it will be years before answers to your questions will be allowed to be given. There are tests, studies and trials that first must be accomplished..and there is that behemoth dinosaur, better known as the IRB…

    Is it ethical to wait the 100 years perhaps necessary before research will completely substantiate the curative powers of vitamin d? Personally, I don’t think so…what I read and study indicates to me that vitamin d is extremely safe, and just might be an effective ancillary treatment to standard chemotherapy protocols. But, I’m not a physician or researcher…I am just an average gal who is fanatically addicted to vitamin d information. I guarantee you that there are mainstream medical doctors and scientific researchers who would argue with me that the 100 years of research are indeed very necessary.

    Here is something I’d like to stress:

    The Vitamin D Council is a wonderful website (I think everyone can tell that I’m totally smitten with it). But, it isn’t and can’t be a forum for specific medical advice.

    You need to be under the care of a qualified and knowledgeable vitamin d doctor…preferably a vitamin d oncologist.

    To find such a doctor is a difficult task for sure.

    It is one of my many vitamin d focused dreams to see a directory of such physicians developed. But, to develop such a directory is very difficult, and would require some sort of authenticity verification..a certification process of sorts…I know that the VDC is ahead of me on this idea (and that’s why I LOVE this organization…it is always one step ahead of the game).

    I hear that there are doctors in Brazil (particularly a man by the name of Cicero), who treat autoimmune diseases with such high dosages of d3 as to get the 25(OH)D level up around 160 ng/ml. These doctors are seeing amazing results. Perhaps there are oncologists in Brazil doing similar such work?

    I do have a multitude of health conditions which I successfully keep controlled with a 25(OH)D level at the highest end of optimal. I would like to emphasize that this is my personal choice…again, I am not a healthcare professional, physician or researcher (though how I wish I were…I would kick up a storm in the mainstream world).

    I hope that my answer has assisted you in some small way, as I truly feel a calling to be of service in the Vitamin D scene.

    Best of luck,
    (203)785-6269 (m-f, 9-5 ET)

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  6. Magic says:

    Hi Ms larma.

    Rita has brought up some really good reasons to attack your problems with as much D3 as you can comfortably take. That is you should first immerse yourself with knowledge. Rita is on one coast and I am on the other…. We can go on for days giving reasons of successes.

    Both of us are completely sold. You , too, need to be SOLD that it will help. You have problems that are serious. The right amount of these little pills or sunlight could solve your ordeal.

    Some of the most respected doctors in your city will tell you that 1000 units a day will poison you. Rita and Magic know that is not true. We are not medical people. Medical people don’t respect what we are trying to do.

    I would suggest taking at least 10,000 a day. If you seem to be improving, I would take as much as it takes until the problem is gone.. That is, keeping in touch with the studies that have shown an amount that has proven safe.

    My number is 541 654 0225 …..in Eugene, oregon


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  7. Rita and Misty says:

    Magic, et al….

    Isn’t it wonderful how small our globe has become?

    Today, with the advent of technology, it matters LESS if friends are on opposite sides of the coast, or the world, now-a-days.

    I routinely talk with vitamin d friends from all over the world. I’m looking forward to doing something with SKYPE (at the encouragement of a long-time friend here in New Haven).

    Additionally, I think it would be wonderful to hold a VDC membership meeting so we all could get to know each other. I would be there, for sure!

    Perhaps it is coincidence, but everyone and anyone seriously interested in D seems to be friendly, intelligent and easy to talk with…I know I am….

    Magic…I’m uncertain about your reference to being SOLD…I think that these things either resonant with someone or they don’t…. I have yet to convert anyone to D (or anything else) by chasing them down…


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  8. Magic says:


    My comment comes from what I have found from people that really need D3. They should get immersed to SELL themselves. So many buy some, use it for a while in small amounts and then sort of forget it. I hate to say that the drug companies are working against us with big bucks………..BUT THEY ARE!

    These people may be risking their lives. I saw a really positive article last week. The last sentence. however, warned the reader that D3 may cause kidney stones. …………In the years that I have been taking D3 and studying it, I have never heard of anyone getting kidney stones from D3 usage. Sounds scary though, doesn’t it.

    Keep up the good work!!


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  9. Rita and Misty says:


    Potassium and Magnesium prevent kidney stones.


    I did have a bout of kidney stones back in late fall 2012. Really not certain why, as I eat an extremely healthy diet, filled with veggies, seeds, nuts and (limited) fruit (due to sugar content). I wouldn’t wish kidney stones on my worst enemy. Just awful.

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  10. Magic says:


    I am really surprised. I haven’t ever seen a mention on it before. I know it is terrible. That is why I figured it is a “scare tactic.”


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  11. Rita and Misty says:

    Hey there Magic…

    Dr. Cannell has written on this topic, on more than one occasion, for sure.

    And, I think he would agree: Vitamin d3 does not cause kidney stones!

    Not certain if it is a “scare tactic” or just plain ignorance on the part of mainstream medicine.

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  12. Rebecca Oshiro says:

    It’s interesting that, according to the graph, the vitamin D made from sun exposure stayed in the system longer. The oral dose peaked the serum level much more rapidly and effectively, but it declined in a similar fashion.

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