DEAR DR. ROACH: I have a severe vitamin D deficiency. My blood test indicates a level of 21. I have severe cramps in my hands, feet and legs caused by this deficiency. I know because when it is normal, I don’t have the cramps. These numbers are after I have been taking megadose vitamin D2 (50,000 IU). At my last appointment, my doctor said, “For some reason, your body is not accepting it.” She then gave me another prescription for the same. Any suggestions? — G.D.

ANSWER: In general, when something isn’t working, don’t keep doing the same thing and expect a better result. Still, I agree with your doctor that your body isn’t absorbing the vitamin D. This should prompt a search to find out why. Celiac disease, pancreas enzyme insufficiency and history of bariatric or stomach surgery are the most common causes.

Vitamin D2 isn’t quite as effective as vitamin D3. If no cause is identified, it might be worth high daily doses of D3 and careful monitoring of your blood level.

Finally, make sure your doctor is checking the right blood level. If she is giving you D2 and checking D3 blood levels, that would explain the discrepancy (but it would not explain the cramps, which can be a symptom of severe vitamin D deficiency). In my lab, I order the combined D2 and D3 level.

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