Vitamin D Deficiency: Is It Really As Common as People Say?

Do you prescribe vitamin D, take vitamin D or have been told you are vitamin D deficient?  If so, you should read an article published the other day in the NYT (19 August 2018, Sunday Business Section) .  The article was entitled: “Shadows on a Sunny Fad,” and was written by Liz Szabo.  The article was mostly about a physician, Michael Holick, who has been a strong proponent of vitamin D use for many years.  Apparently Dr. Holick has been handsomely rewarded by the drug industry and some clinical laboratories that measure blood vitamin D levels for pitching the wonders of vitamin D and the fact that many, many people are vitamin D-deficient and don’t know it; many physicians have been persuaded by Dr. Holick and others that the normal range for blood levels of vitamin D have been far too low, and that we should adjust the normal range upward.  The lower limit of normal used to be about 10 nanograms per milliliter (the laboratory test is serum or plasma 25-hydroxyvitamin D), but now it is 30 nanograms per milliliter.  (Note: As an aside, based on what I have read, in my opinion, Dr. Holick has been mostly an overzealous physician, obsessed with the benefits of vitamin D supplementation, and not an evil-doer, in it for the money, as the article hints at.)

Are many of us really vitamin D deficient?

The article makes very clear that little or no compelling data have supported the push to raise the upper limit of normal for blood levels  of vitamin D.  To me it is simply astonishing that most physicians and even endocrine specialty organizations have “bought into” this nonsense, despite recent data showing that the upward readjustment of the lower limit of normal for blood vitamin D levels is not scientifically justified.

Is treatment with vitamin D supplements dangerous?

It is indeed fortunate that for most people who are not really vitamin D deficient, the recommended vitamin D dosages are not much above the recommended daily allowances for vitamin D intake.  But, as the article points out, large doses of vitamin D are toxic and can cause serious health problems.  Old physicians (like me), remember when the only medicines available to treat patients who were truly vitamin D deficient or who had low blood levels of calcium for reasons not related to vitamin D deficiency, were precursors of the actual active form of vitamin D (1.25-dihydroxy vitamin D), which is made in the kidney from vitamin D.  The precursors to the active form of vitamin D can easily cause dangerously high blood levels of calcium (hypercalcemia), which can lead to irreversible kidney damage.  The worst part is that these precursor vitamin D products are fat-soluble chemicals, and if taken in excess, will sit around in the fat cells for a long. long time, and continue to cause hypercalcemia.  Now days, we can just give patients 1.25 dihydroxy vitamin D (calcitriol or Rocalitrol).  This drug is identical to the chemical made in the kidneys, and has a very short half-life in the body, and if it causes hypercalcemia, the problem can be corrected quickly.

What is the “bottom line” here?

As I mentioned above, modest doses of vitamin D (e.g., less that 2000 IU/day) are unlikely to cause problems, even in people who were not vitamin D deficient before they started taking the medication.  In my opinion, blood levels of 25-hydroxy vitamin D over 15 or 20 nanograms per milliliter are probably fine and dandy, and do not need any fixing.  For people taking large doses of vitamin D (or even 1,25 dihydroxy vitamin D), the best way to monitor treatment is to measure 24-hour urinary calcium.  If it is less than 200 mg/24 hours, all is well.

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