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Activated vitamin D vs 25(OH)D levels: What should you measure?

Posted on: December 28, 2012   by  John Cannell, MD


The good news is that few doctors treating osteoporosis are making the same mistake they made so often 5 years ago, that being to measure activated vitamin D levels (calcitriol) instead of measuring 25(OH)D levels .

Unlike 25(OH)D, calcitriol in the blood is an adaptive hormone; it is inversely related to the amount of calcium in the intestine. If there is no calcium in the intestine, calcitriol levels go up to remove calcium from bone making osteoporosis worse. If calcium is present in sufficient quantities in the intestine, that calcium is absorbed and activated vitamin D levels fall.

Calcitriol in the blood, for just one draw in one patient, has little relationship to 25(OH)D levels. In fact, 25(OH)D levels are often low when calcitriol levels are high. The reference range for calcitriol is usually 17–75 ng/L for healthy adults.

A few months ago, I got a letter from a woman who mistakenly had her calcitriol levels measured. Her calcitriol levels were high even though her 25(OH)D  levels were low. I recommended that she take extra calcium in her diet and also take a supplement that contained calcium, magnesium, K2, and zinc. I also recommended that she take 5,000 IU/day of vitamin D even though her activated vitamin D levels were high. Below is her follow up letter.

Hi Dr Cannell:

I wanted to keep my promise and follow up with you regarding the high calcitriol that had everyone so concerned.

You instructed me to start taking at least 1000 mg of Calcium/Mg/ZN daily. I also began taking 5,000 IU/day of D3.  I have begun drinking milk again and my calcium intake has come closer to 2000 mg daily over the last two months.

  • On 10-12-2012 the calcitriol level was 128 ng/L.
  • On 11-12-2012 the level was 95.0
  • On 21-21-2012 the level was 62.0.

Looks like the your advice is working! I hope that it will now start reversing my osteoporosis.

Thanks so much.

Lisa, Minnesota

Dear Lisa:

I am glad. Remember many things, including an acid environment in the body, cause osteoporosis. Be sure to eat alkalizing foods, such as vegetables, or, second best, get your doctor to prescribe potassium bicarbonate, 25 meq (900 mg) as effervescent tablets and dissolve one tablet in 8 ounces of water twice a day and drink it. That will give you less than half of the 4.7 grams of potassium the Institute of Medicine recommends daily but it will turn your urine from acid to basic. Studies show potassium bicarbonate may well help things other than your bones.

Morris RC Jr, Schmidlin O, Tanaka M, Forman A, Frassetto L, Sebastian A. Differing effects of supplemental KCl and KHCO3: pathophysiological and clinical implications. Semin Nephrol. 1999 Sep;19(5):487-93. Review.

I also always think it is wise to eat leafy greens, which have some magnesium and calcium as well, particularly the hardy ones like kale. This, in turn, helps with two areas: increasing your magnesium and calcium intake and increasing your alkalizing food intake.

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