Coffee drinkers, what do those genes say about your health?

Coffee drinkers, the urge to refill your mug may be in your DNA, scientists said this week, adding that people with one of two “caffeine genes” drink about half a cup of coffee more every day than those without the genes. The next question is:

Is there any harm in giving in?

Conjectures on whether coffee lovers should rejoice or weep over their compulsion seem to oscillate continually. It raises blood pressure; no, it lowers it! Drink regular; no, drink decaf! And so on…

One possible reason for the discrepancies is because, in studies on coffee-drinking habits, scientists don’t ask people to drink the same amount of coffee every day. Instead, people recall how much coffee they drank. So it’s difficult to conclude that any health pros or cons are caused by the coffee rather than something else (for example, smoking) that coffee drinkers might also do.

Still, a number of studies do appear to agree in some respects, and the verdict seems to lean toward going for the extra cup. Here are some reasons why:

-- Coffee appears to lower the risk for Type II diabetes, perhaps by as much as 50%. Both regular and decaf seem to have the same effect, probably because of antioxidants in coffee. For example, an ingredient called chlorogenic acid slows the uptake of sugar in the intestines.

No evidence yet on whether a grande white chocolate mocha at Starbucks -- with its whopping 470 calories -- neutralizes that anti-diabetes effect.

-- Coffee may lower the risk of heart attack and stroke. In one study, people who drank one to three cups of coffee per day were 20% less likely to be hospitalized for irregular heart rhythms than were non-drinkers.

In another study, women who drank two or more cups per day were 20% less likely to have a stroke than women who drank less.

-- Coffee (but maybe not decaf) may reduce the risk of Alzheimer’s or dementia. In one study, drinking three to five cups in middle age cut the risk for dementia by 65%. Caffeine is probably the main actor here.

Evidence is stronger that drinking lots of coffee might lower the risk of Parkinson’s disease. Coffee-drinking men appear to have half the risk of developing the disease compared with nondrinkers. Again, it appears that caffeine — about the amount in one cup of coffee — is what might be bringing the risk down (but most people’s risk for Parkinson’s isn’t very high to begin with).

-- Coffee doesn’t have much of an effect on cancer, except maybe, just maybe, to reduce the risk of liver cancer (and cirrhosis, another liver disease).

Again, these are association studies, meaning researchers haven’t found any direct cause and effect. But they did find correlations between drinking coffee and health. Now for a look at what scientists actually know.

First, coffee isn’t too harmful.

-- Coffee helps headaches…sort of.

Caffeine certainly can cause headaches, dizziness, insomnia and shaking. But it can ease migraines and headaches. That’s because blood vessels expand at the beginning of a headache, but caffeine causes the vessels to narrow.

-- Studies haven’t found much of an effect from coffee on cholesterol, as long as you drink your coffee filtered. Unfiltered coffee, such as that made in French presses, drips in a substance called cafestol, which seems to increase “bad cholesterol.”

But the caffeine in coffee has a few drawbacks:

-- Caffeine causes short spikes in blood pressure. But many people build a tolerance after a week or so. And there are other substances in coffee that counteract caffeine, unlike in caffeinated sodas.

-- Caffeine is a mild diuretic. It makes you go to the bathroom more often.

Overall, any stress over what may or may not be a genetic propensity to like coffee may be unwarranted. Coffee isn’t harmful for most people and may even be helpful.

Bottoms up.