DEAR DR. ROACH: I drink a lot of coffee, about 80 ounces per day. I feel no ill effects and have no stomach discomfort, but my wife says water is better. A kidney specialist basically said, “fluid is fluid” and that as long as I am hydrated, coffee is fine. With studies showing that coffee has antioxidants and reduces certain cancers, what should I do? — M.K.

ANSWER: People with long memories may recall that in the early 1980s, coffee was linked to an increased risk of pancreatic cancer. However, the study has become a textbook example of poor design, and further studies have suggested that coffee drinking may be associated with lower risk of breast, prostate and oral cancers. I wouldn’t recommend drinking coffee just for this reason, as the effect size, if it really exists, is pretty small.

As far as hydration goes, your kidney specialist is completely right. The caffeine in regular coffee is perceived as a diuretic (a substance that makes you urinate excessively), but that turns out to be myth as well, at least in regular coffee drinkers.

One potential ill effect of caffeine is that it minimally decreases calcium absorption. However, this amounts to the equivalent of calcium in a tablespoon or two of milk, so it is unlikely to affect overall calcium balance significantly.

Eighty ounces of coffee is a lot of caffeine, and some people will get jittery or have sleep disturbances. It also can have variable effects on gut motility (that’s a delicate way of saying that it commonly causes diarrhea, but it also can cause constipation). All that said, if you aren’t having any ill effects from drinking so much coffee, coffee is fine — though I still think that, as your wife says, water is better for many people.

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DEAR DR. ROACH: I am a 64-year-old male. I had a stroke and lost vision in my right eye in 2005. I am right-handed. I had very high blood pressure at the time, and it’s now under control with drugs. Since then, I can no longer wear polarized sunglasses. I have light-sensitive eyes, but most over-the-counter sunglasses are polarized.

My ophthalmologist and other eye specialists tell me they’ve never heard of my problem occurring. With polarized glasses on, I see in 3-D. Blue lines in the roadway and sewer lids or any metal covering appear to be 3-D to me. I have to be careful stepping over the handicap space lines because they look like curbs.

Have you ever heard of this, or am I unique? If I can locate nonpolarized lenses, then I have no problem. Thank you. — J.O.

ANSWER: While everyone is unique, this is a condition I have heard of before. In fact, I know people who deliberately watch television with one eye in order to enhance the 3-D effects. Polarized light does tend to accentuate lines and edges, so it doesn’t surprise me that with your one working eye you have an accentuated 3-D sensation — your brain has learned to use cues that people with two working eyes might miss. In your case, the brain has interpreted things so strongly that you are having some optical illusions.

Sadly, I don’t have any practical advice beyond finding nonpolarized lenses.

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.

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—TO YOUR GOOD HEALTH: In hydration game, coffee counts–