Dear Dr. Roach: Please give your take on the importance of vitamin D. I’ve read it greatly reduces cancer risk for most types of cancer and that it activates anti-infection genes and anti-autoimmune disorder genes and reduces the rate of Alzheimer’s disease.

I’ve also heard the dose needs to be high enough to get to the middle of the “normal” range, and for adults that is a dose of 5,000 to 7,000 IU.

Considering the above, it really annoys me that the major organizations fail to publicize prevention information.

J.M.

Dear J.M.: I have seen many proposed preventive treatments for cancer fail when they get tested in large trials. I am thus cautious not to overstate the benefits of promising small trials and epidemiological data, such as the kind you mention above. It is clear that vitamin D has significant benefits in specific circumstances, especially in bone health, where inadequate vitamin D is associated with a greater risk of osteoporosis and fracture. And although the studies do show that people with higher levels of vitamin D are less likely to develop some cancers, especially in the colon, a study published in October 2015 found that vitamin D did not prevent the development of polyps.

Large trials are ongoing. They will give us much more information within a few years. Until then, I remain cautious about vitamin D and confident that the major organizations wish to see more proof before making recommendations.

The standard dose of vitamin D is 1,000 to 2,000 IU. Although 5,000 or even 7,000 is unlikely to cause harm, I wouldn’t recommend a dose that high without cause.

Dear Dr. Roach: I am a 75-year-old woman with stage 3 kidney failure. How many stages are there? What symptoms occur in higher stages? How can I slow progression?

T.S.

Dear T.S.: Chronic kidney disease has five stages based on measuring how well or how poorly the kidneys filter blood to cleanse it of waste materials. Since high blood pressure is both a cause and a consequence of kidney malfunction, close monitoring of blood pressure is one way to slow the decline of kidney function. Your doctor will tell you — based on lab tests, which are more reliable than symptoms — if you need a special diet.

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