Risk of developing high blood pressure stems from caffeine in sodas, not coffee

Anyone who knows me well knows that I often have a latte or a Diet Coke in hand. Lately I’ve turned to decaf in both my coffee and Coke, having decided to take my own advice and limit caffeine intake as a way to manage my leaky bladder. It works, by the way, just as I wrote.

And since I’ve flirted with high blood pressure in the past, I read with great interest a recent article in the Journal of the American Medical Association that looked at caffeine use in women and its association with high blood pressure. We know that caffeine raises blood pressure in the short term. But until now, studies have been brief, lasting only a week or so. What happens if you’re a caffeine regular, if you drink coffee or caffeine-containing beverages on a daily basis? It seemed logical to assume that long-term use would spell trouble as well.

Well, that’s why studies are so important. “Don’t believe everything you think,” my bumper sticker says, and here’s a perfect example.

Researchers at Harvard Medical School used data from the Nurses Health Study (I and II) to assess whether caffeine intake raised the risk of developing high blood pressure in the future.

This is an important question, since approximately 50 million Americans have high blood pressure. Many more than that are caffeine drinkers. People who have high blood pressure are at risk for getting heart disease, stroke and congestive heart failure. So, if we identified caffeine as increasing the risk of high blood pressure, there would be an obvious intervention. (Decaf anyone?)

Researchers identified 155,594 women who were free from physician-diagnosed high blood pressure in 1990 and 1991. They followed these women for 12 years with bi-yearly questionnaires. Included in the questionnaire were questions about dietary habits, including caffeine consumption. The relevant beverages on the questionnaires were diet cola (Diet Coke and Diet Pepsi), regular cola (Coke, Pepsi and other cola beverages with sugar), tea with and without caffeine, coffee with caffeine, and decaffeinated coffee.

Then, the researchers calculated total caffeine consumption based on the questionnaires. Using Department of Agriculture data, they assumed that a cup of coffee contained 137 milligrams of caffeine, tea contained 47 milligrams, a can or bottle of cola contained 46 milligrams and a serving of chocolate candy contained 7 milligrams of caffeine. (Whose serving, I wonder?)

Over the course of 12 years, 13,077 women developed high blood pressure. Mean daily caffeine intake ranged from 20 milligrams a day to 600 milligrams a day (now there’s someone with a habit!)

Here’s the surprise (remember my bumper sticker). Those who drank lots of caffeine were no more likely to develop high blood pressure than those who had no caffeine in their diets. In fact, there was a slight decrease in blood pressure in the women who drank a moderate amount of caffeine. So all those lattes might be OK – plus, we’re getting all that calcium!

Here’s the next surprise. The question was whether caffeinated colas, either diet or sugared, increase the risk of getting high blood pressure. For the women who drink the highest amount of the soft drinks, the risk of developing high blood pressure increases by almost 80 percent compared to those who leave the Coke or Pepsi on the shelf.

Of course, no one has a clue why cola beverages increase your risk and coffee doesn’t. Is it some compound in the soft drink that isn’t found in coffee? That would be a logical conclusion, but then one has to wonder if that compound, or compounds, is present in other soft drinks, particularly dark ones, like root beer and Dr. Pepper. And this study was of predominantly white women, so no conclusions here about men, or women of other races.

As always, we need more studies. For now, women at least, can hang on to their caffeinated java. As for the Diet Coke fiends among us, it may be a different story.