Dear Dr. Roach: I recently received my blood test results. My overall vitamin D was 40 (within the target range of 30 to 60 listed), but I noticed that it was broken up into vitamin D-3 (also 40) and vitamin D-2 (less than 4, and presumably 0 based on the overall score). What is vitamin D-2, and should I be taking supplements or eating certain foods to boost its levels?

-- P.S.

A: Both vitamin D-2 and vitamin D-3 are found in diet and in supplements. D-2 is found at low amounts in vegetables; D-3 is found in some fish. Both D-2 and D-3 are used to fortify milk and other dairy products. The body normally makes vitamin D-3 when your skin is exposed to sunlight. Without adequate sunlight (such as in the winter north of the line from Los Angeles to Atlanta), it's very difficult to get adequate vitamin D without supplementation. The fact that your D-3 is much higher than your D-2 suggests that you are taking supplemental D-3 or you are getting adequate sunlight (or a combination).

Both D-2 and D-3 are converted in the kidney to the active form of vitamin D, called 1,25-dihydroxyvitamin D. (Only people with kidney disease require this form of vitamin D supplementation.) This is the form that is necessary for bone health and has a role in maintaining many other processes in the body. It is not yet clear whether supplemental vitamin D will reduce the risk of heart disease and cancer, but an ongoing study hopes to answer that question.

It's the overall vitamin D number that you need to be concerned about, not the individual components, so there is no need for a D-2 supplement. I generally prefer D-3 for supplementing; it seems to provide better levels and lasts longer. The target overall blood level remains controversial, with some experts saying that over 20 is adequate, while others recommend levels of 40 (or even higher). However, virtually everyone would agree that your level of 40 does not need treatment. I would not recommend further supplementation or changing your diet for the sake of vitamin D.

Why we sneeze

Dear Dr. Roach: Every time my husband finishes a meal, he starts to sneeze. Not only once, but maybe five or six times. Is this normal? Why does he do this?

-- E.C.

A: Sneezing is a neurological reflex, normally triggered by inflammation in the nasal passages, such as in people with upper respiratory tract infections or people with allergic rhinitis. However, some people can develop nasal discharge while eating (this is called "gustatory rhinitis"), and this may trigger the sneeze reflex. There are other nerve reflexes that can have the same effect, including the photic sneeze reflex, when people sneeze uncontrollably when looking at the sun or another bright light source, which interestingly is a dominant genetic trait.

I often have been asked why people don't sneeze once, but several times in a row (some people attach significance to the number, but these suppositions aren't based in science). The answer is that while sneezing propels the fluid in the nasal passages a surprising distance and at considerable velocity, it does not immediately stop the inflammation, which is the trigger for the sneeze.

Treatment for sneezing is mostly to reduce inflammation in the airways, which can be done with oral or nasal antihistamines, nasal steroids and other anti-inflammatories.

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The booklet on colon cancer provides useful information on the causes and cures of this common malady. Readers can obtain a copy by writing: Dr. Roach, Book No. 505, 628 Virginia Dr., Orlando, FL 32803. Enclose a check or money order (no cash) for $4.75 with the recipient's printed name and address. Please allow four weeks for delivery.

Dr. Keith Roach writes for North America Syndicate. Send letters to 628 Virginia Dr., Orlando, FL 32803 or email ToYourGoodHealth@med.cornell.edu.

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