Vitamin D: the never-ending saga

vitamin DVitamin D is in the news again.  Is it ever not in the news these days?  This time it’s an opinion piece written by Dr. Tod Cooperman, MD, who founded ConsumerLab.  His main point: vitamin D has been promoted as a cure-all for everything from osteoporosis to inflammation and heart disease.  And as a result too many people are taking vitamin D supplements, possibly leading to excessive blood levels.  You can get too much of a good thing.

To support his argument, Dr. Cooperman references a recent study on post-menopausal women that seemed to show that high dose vitamin D supplementation (50,000 I.U. twice a month, or a daily average of 3300 IU), which raised blood vitamin D to above 30 ng/ml, didn’t significantly increase calcium absorption and didn’t result in any significant improvement in bone mineral density.  OK first thing I noticed about this study design: the women subjects didn’t have osteoporosis.  So I have to ask: if their bone mineral density was already fine, why would we expect it to get even denser?

Here’s an even bigger problem with that study, and with the vitamin D/bone density question in general: Bones are complex living tissue.  They are not just lumps of calcium.  Vitamin D may improve calcium absorption, but calcium is just one piece of the bone density puzzle.  Numerous other nutrients are also critical for bone health:

  • protein
  • potassium
  • phosphorus
  • magnesium
  • other trace minerals
  • vitamin K

Nowhere in this study does it say the women were evaluated for their status or intake of any of those other key bone nutrients.  So why should be imagine that just focusing on vitamin D and calcium was going to result in meaningful information.  I’m not impressed by this study at all.

Nevertheless, Dr. Cooperman has a point about the widespread overuse of vitamin D by people who are not deficient.  As he points out, some labs that test for D set the “normal” blood level range at 20 – 100 ng/ml.  So if an uninformed person sees that their level is say 30 ng/ml, they may conclude that taking more vitamin D and raising that level will be even better.  This is a problem, aggravated by the fact that this one vitamin is being touted as a magical cure-all.

Another problem: ConsumerLab has found that many vitamin D supplements contain far more vitamin D than claimed on the label.  And there’s no way for the average shopper to know the difference.  If you only get your vitamin D tested once a year, you might have an acceptable level one year, and an excessive level a year later thanks to excess supplement intake.  Vitamin D is a fat soluble vitamin, meaning excess intake is not flushed out of the body by the kidneys.  Amounts consumed above daily use accumulate in the body.  Excess accumulation can eventually cause toxicity symptoms.

Sufficient vitamin D, combined with a healthy intake of all other nutrients in the context of a healthy balanced diet is fine.  Throwing excessive amounts of vitamin D onto an unbalanced diet and unhealthy lifestyle, and expecting it to fix all your problems, is foolish.  Don’t just dose yourself up with vitamin D without being tested.

For more information about vitamin D, including it’s many biological functions, I recommend the Linus Pauling Institute’s Micronutrient Information Center.

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