Sugary drinks and high blood pressure -- a link?

I expect consequences from drinking lots of sugary sodas. Like: unneeded calories, possible spikes in blood sugar, slow but steady erosion of tooth enamel (if those oft-repeated science fair projects with the teeth in the plastic cup of Coke are to be believed) and caffeine jitters.

But a rise in blood pressure? A study just published in the journal Hypertension argues that you might be in for that if you have a sugary-beverage habit.

The finding comes from the so-called INTERMAP study, which stands for International study of Macro/Micronutrients and Blood Pressure, which kind of works as a name if you ignore words like “study” and “blood.” This particular INTERMAP report analyzed data from 2, 696 middle-aged adults in the U.S. and U.K. On several occasions, their blood pressure was taken. Urine samples were taken for two 24-hour periods. Information about their diet in the previous 24 hours was collected.

Each extra serving of sugar-sweetened beverage daily led to an elevation of systolic blood pressure of 1.6 millimeters of mercury (mm Hg) and an elevation of diastolic blood pressure by 0.8 mm Hg higher blood pressure readings, reported Ian Brown of Imperial College London and colleagues. This didn’t hold for diet beverages: In fact, the opposite relationship was seen for diet drinks. The finding appeared to be stronger for those who consumed more sodium and was independent of caffeine, plus the researchers did try to control for other lifestyle factors as well as height and weight.

Related: Diet soda and heart, stroke risk: A link doesn’t prove cause and effect

The scientists note that animal studies already report that extra glucose and fructose are known to have an effect on blood pressure, and there are a few human clinical trials that suggest the same thing, so the observation is not physiologically nutty. They particularly mention the PREMIER study (all studies have to have a jazzy name these days, it seems), in which 810 people with hypertension or so-called prehypertension (higher than healthy but not yet over the line into full-blown hypertension) were coaxed to reduce their sugar intake over 18 months and managed to lower their blood pressure somewhat.

How might the effect work? For fructose, the scientists offer this explanation: Fructose is ultimately metabolized to uric acid, which can cause the body to reduce blood levels of nitric oxide. Nitric oxide dilates blood vessels — so if you have less of it around, it makes sense that blood pressure would rise some.

The scientists also note that sugar consumption can lead to sodium retention and a revving-up of the sympathetic nervous system, both of which can also increase blood pressure.

Now for the caveats:

This was a cross-sectional population study. In other words, it’s not like someone’s directly controlled similar people’s sugary-beverage consumption. There could be differences between the groups of people who drank or didn’t drink sugary beverages. Nor had the scientists tracked people for years, having first ascertained that they drink sugary sodas, then watched to see what happened to them. So there’s no “this came first, then that” established here.

And the study (like many food-disease studies) depended on people remembering what they ate. People aren’t that good at such recall, even if it’s about yesterday. And if they know they’re in bad shape it’s possible they’d be more likely to report consuming things that are bad for them.

Here’s another: “residual confounding,” as the authors put it. In other words, try as you might to factor out other habits of diet and lifestyle that might go along with drinking sugary sodas, it’s pretty hard to do that 100%. Crappy habits do tend to band together.

But the science, at least, suggests several mechanisms, and it wouldn’t hurt to cut down on sugary drinks anyway, we’re guessing. Finally, here, as listed in the paper, are a few items that seem to be firmly linked to high blood pressure: “high sodium intake, inadequate potassium intake, high body mass index (BMI), and excessive alcohol intake.”