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Dear Dr Cannell: Vitamin D malabsorption

Posted on: October 19, 2012   by  John Cannell, MD


Dear Dr. Cannell:

I’ve been taking 2,000 – 5,000 IU of Vit D and when I was tested recently, it was only at 21. I live in New England, so there is not much sun although this summer, I sat outside in the sun for 20 mins once or twice a week. How can I get my level up?

I read that if you have gut dysbiosis, your body cannot absorb the Vit D. Is that true?


Sally, Vermont

Dear Sally:

Without knowing how long you took 5,000 IU per day before your blood test, and without knowing when you went into the sun and with how much clothing, and what your baseline level was, it is difficult to answer your first question. It may be malabsorption, it may be a very low initial level, it may be genetics, it may be unproductive sun exposure, and it may be an error in the test.

For whatever reason, you are still apparently deficient and need to take 5,000 IU every day and test again in three months. Also, take your vitamin D with your largest meal of the day for better absorption. I have written some mixed advice in the past on whether you need to take with a meal, as the research is inconsistent. However, if you’re having malabsorption issues, there is no reason not to try taking vitamin D with largest meal of day.

Mulligan GB, Licata A. Taking vitamin D with the largest meal improves absorption and results in higher serum levels of 25-hydroxyvitamin D. J Bone Miner Res. 2010 Apr;25(4):928-30.

I am unaware of any evidence that intestinal dysbiosis is associated with malabsorption of vitamin D, but I would be surprised if that were not the case. Dysbiosis (unhealthy imbalance in intestinal flora) is associated with a number of intestinal and immune maladies. As vitamin D is involved in signaling between the gut microbes and the immune system both, treating both dysbiosis (with probiotics and prebiotics) and your vitamin D deficiency may help your dysbiosis.

Ly NP, Litonjua A, Gold DR, Celedón JC. Gut microbiota, probiotics, and vitamin D: interrelated exposures influencing allergy, asthma, and obesity? J Allergy Clin Immunol. 2011 May;127(5):1087-94; quiz 1095-6. Epub 2011 Mar 21. Review.

Finally, please write again in three months with the results of your vitamin D blood test, so we know how you are doing.

John Cannell, MD

13 Responses to Dear Dr Cannell: Vitamin D malabsorption

  1. kenmerrimanmd

    certainly seems to me in the relatively short time I have been looking at this that doses above 5000iu are sometimes indicated esp with larger people which is a large proportion of my patients anyway

    for those with a really empty “bucket” it also seems reasonable to kind of crank up the dose for awhile to get the bucket full and since we are thinking that Vit D toxicity is soooo rare this seems to me a pretty good strategy

    would be interested to hear what Dr cannel thinks about this


    ken merriman md

  2. [email protected]


    I’m just a layperson, but I share your philosophy completely.

    I wonder if multiple chronic health conditions in one individual would require him or her to need a much higher dose of Vitamin D to maintain adequate serum levels?

    This seems like common sense to me. Would love to read what others think re: this question.

    Thank goodness for this online community!

    Such a great resource.


    Rita C. Umile

  3. Brant Cebulla

    In “The Pharmacology of Vitamin D” (Vitamin D: Third Edition), Reinhold Vieth proposes a systematic approach to using “loading doses” to quickly treat vitamin D deficiency. He proposes a formula of…

    Loading dose = (Daily Maintenance Dose) x (60).

    The 60 represents days of vitamin D half-life. So if you believed that someone needed 1,000 IU/day to maintain optimal vitamin D levels, you would prescribe a loading dose of 60,000 IU to kick off the maintenance regimen.

    If we looked at 4,000-5,000 IU doses, sort of the range that vitamin D advocates call for, this would equate to loading doses of 240,000 IU-300,000 IU to start the regimen. He does warn that it is probably better to segment such a loading dose into weekly loading doses of less than 100,000 IU. So instead of taking 300,000 IU, spread that over 3 weeks of 100,000 IU doses.

    I’m not a Dr, but seems like maybe a slight overkill approach for the higher dosing regimens of 4,000-5,000 IU (not that clinical toxicity is of concern), and more built for what government recommendations may be headed toward of around 2,000 IU/day.

  4. [email protected]

    There is a form of vitamin D proven to work well for those with poorly functioning guts.

    Bio-D-Mulsion Forte, which is similar in cost to regular vitamin D

    details at http://is.gd/gutvitd

    Also: Overview on loading dose of vitamin D


    Also: Overview of Kidney and vitamin D (in case it is a problem of the kidney not activating the vitamin D


    And lastly: How you might double the benefit of your vitamin D


    which includes time-of-day, cofactors, almonds, Magnesium, etc.

  5. John Cannell, MD

    Dr. Merriman:

    I think loading doses, not to exceed 50,000 IU/day can be useful when someone is ill or has a disease that may respond to D. For example, 50,000 IU/day for a week or two followed by 5,000 IU/day will get someone’s level up rather quickly.

    As far as maintenance dose, the rule is 1000 IU/25 pounds of body weight as an estimate but if that dose exceed 10,000 IU/day we recommend a periodic 25(OH)D.

    As so much of vitamin D levels are heritable, one really does not know if you have an excess or not enough without a blood level.

    However, if the patient gets no sun exposure and takes no vitamin D, the initial test will be low and is kind of a waste unless the physician or patients wants to be satisfied. If the patient is stable, just start on 1,000 IU/25 pound and get the 25(OH)D in 2-3 months.


  6. Angelo Kostas

    If the above individual has been supplementing D3 consistently, and her 25hydroxyvit.D3 is still low, she may want to have her magnesium level checked. Some Americans are deficient in magnesium, and the latter mineral is essential for the utilization of D3. I know of one individual supplementing 10,000 IU of D3 daily for three months, and had a 25hydroxyvit.d3 of 27 ng/ml. ( level prior to D3 supplementation was 26 ng/ml). Further blood work revealed low magnesium level, and after adding a magnesium supplement, the individual’s 25hydroxvit.d3 was rechecked three months later at 63 ng/ml. However, one must be careful because magnesium may cause Hypotension. In any case, some foods which have adequate amounts of magnesium are: Spinach, Beans, Cashews, Almonds, Pistachios.

    Best Regards,

    Angelo, RD, LDN

  7. [email protected]

    It’s hard to get enough magnesium (IMO) from the standard American diet.

    In particular, if you are calcium heavy in your diet, you may need up to 600 mg/daily of magnesium.

    Google will provide a wealth of information on this subject.

    On a personal note, I find that 400-600 mg of magnesium citrate taken in the evening helps me sleep soundly, and helps with morning regularity as well.



  8. Rebecca Oshiro

    A friend of mine supplemented with 5,000 IU/day for the better part of a year and was never able to get her 25(OH)D level out of the 20’s. (She tried several different brands of supplement.) After a summer of plenty of sun exposure, her level was 43 ng/mL. I always suspected some kind of absorption issue.

  9. [email protected]

    Hi Rebecca,

    Maybe it is an absorption issue for some….

    Yet, I often wonder about those of us (like me) who supplement with mega doses of D3 and yet still test within normal serum levels (30 ng/ml–100 ng/ml)….

    Perhaps folks like me might be utilizing Vitamin D for a multitude of undiagnosed health conditions….

    I know that prior to my supplementing with D3, my hormones were completely out of balance…I was 30% over my body weight…I had trouble sleeping…I was always coming down with this or that bug….

    My health is so much better now.

    Really, it’s just the last few months that I’ve had the courage actually to state that I’m taking 15,000 i.u./daily in summer and 30,000 i.u./daily fall-late spring. I monitor quarterly. I remain below 100 ng/ml.

    Yes, I’m taking a large amount of Vitamin D, for sure…but, apparently it works for me.



  10. Ninabwright

    I have a surgically-induced malabsorption from a weight-loss surgery called Duodenal Switch. I, and several others I know of with the same surgery supplement with over 100,000 IU per day. I took 150,000 IU for a year before getting up to normal levels and have cut back to 100,000. The key is staying on top of it now, and regularly having tests to monitor my levels. Luckily, I have a doctor who will work with me. The DS greatly reduces your absorption of fats, and I have very low chlosterol levels (total cholesterol of 76 on last labs, up from 73) and I wonder if my problems getting my D3 up arise not only from absorption in the gut, but if this low cholesterol level would impair my ability to benefit from exposure to the sun.


  11. danrab

    I have seen no posts to address too much calcitriol. Mine is much too high, yet I do NOT supplement with D3.

  12. Rita and Misty

    Dear Dan. Has your physician examined you for parathyroid disease? This will often cause high calcium blood levels.

  13. Rita and Misty


    Dan, I meant to type “high calcitriol” blood levels.

    And some folks with with primary hyperparathryoidism have slightly increased levels of CALCITRIOL.

    Granulomatous diseases or lymphomas may also produce excess 1,25 (OH)2D (Calcitriol).

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