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.

DEAR DR. ROACH: What can you tell me about neuroendocrine tumor? My 41-year-old nephew passed away from this cancer. He leaves a wife and two children, as well as family and friends. I was reading about this cancer, and the article said a person can live a long time and that it was slow-growing. My nephew was eventually diagnosed with this cancer in July and he passed away a month later. Was he misdiagnosed? — B.B.

ANSWER: I am sorry about your nephew.

“Neuroendocrine tumors” is not one specific kind of cancer, but instead describes a whole group of tumors. Even using the term “cancer” is confusing when discussing these tumors.

It may help to think of them as two groups: The first is well-differentiated neuroendocrine tumors, or NETs. The other is poorly differentiated neuroendocrine carcinomas, or NECs. A “carcinoma” is a type of cancer arising from glandular tissue.

Cells can start off able to become many types of cells (called “undifferentiated,”) and in the right setting will differentiate to be a specialized cell. “Well-differentiated” cells look more like the tissue that they have specialized into. Tumor cells lose differentiation and with it lose the ability to be regulated. These “poorly differentiated” cells tend to grow and spread more quickly.

Some NETs are slow-growing, and are usually described as well-differentiated by the pathologist examining the tumor sample. However, poorly differentiated NECs can have a very rapid clinical course, and it is not at all unusual to succumb to this cancer within months of diagnosis, especially when a person presents at a late stage.

Many experts call NETs cancers since even benign-appearing neuroendocrine tumors have the potential for aggressive behavior. This can include spreading to distant sites. They can arise from many locations in the body, but especially the pancreas and gastrointestinal tract.

This is an area of increasing study by research scientists, with new ways of classifying these tumors in order to provide better prognostic information and better tailor therapies.

* * *

Dr. Roach regrets that he is unable to answer individual letters, but will incorporate them in the column whenever possible. Readers may email questions to ToYourGoodHealth@med.cornell.edu or send mail to 628 Virginia Dr., Orlando, FL 32803.