Drinking fewer sugary drinks can help lower blood pressure, according to research published in Circulation.

The study found that when adults with early-stage high blood pressure cut back on soft drinks and fruit drinks by one serving a day as part of an 18-month-long diet overhaul, they saw distinct drops in average blood pressure.

Although a number of people lost weight in the study -- which would account for some of the blood pressure-lowering effects -- cutting back on sweetened drinks also seemed to have an independent effect on blood pressure levels.

Why that would be isn't clear, but it could be from the sodium in soft drinks, which can increase blood pressure. It might be that the sugar in the drinks increases levels of hormones that can cause blood pressure to rise. Or it might be that high fructose corn syrup used in soft drinks increases uric acid levels, which has been shown to increase high blood pressure.

Whatever the reason, the researchers say that cutting back on sweetened drinks could be a good way to reduce the numbers of strokes and the incidence of heart disease.

For the study, Dr. Liwei Chen, an assistant professor at Louisiana State University Health Science Center School of Public Health in New Orleans looked at data on 810 adults, ages 25 to 79. Most of the volunteers were overweight and had prehypertension, with blood pressures between 120/80 and 159/99 mm Hg.

All participated in the PREMIER study, a U.S.-funded study with a focus on weight loss, exercise, and a healthy diet as a way to prevent and control high blood pressure.

At the start of the study, the volunteers drank an average 295 milllilitres (10.5 ounces) of sugar-sweetened drinks a day – a little less than the size of one serving of pop a day. The drinks included everything from pop to fruit drinks to lemonade.

By the end of the 18-month study, average consumption had fallen by half a serving/day.

After controlling for known risk factors of blood pressure, the researchers found that those who cut back on soft drinks saw an average drop in blood pressure of 1.8 mm Hg in systolic pressure (the top number), and a 1.1 mm Hg decline in diastolic pressure.

While those numbers may sound small, the researchers say they have important public health implications. Even small reductions in blood pressure can lead to substantial health benefits.

"It has been estimated that a [three-point] reduction in systolic blood pressure should reduce stroke mortality by 8 per cent and coronary heart disease mortality by 5 per cent," Chen said.

Such drops could be achieved by reducing sugary drinks consumption by two servings per day, she said.

"Although this study was conducted among mostly overweight adults and many with hypertension, we believe that others will benefit by reducing the consumption of sugar-sweetened beverages," she said.

She says more study is needed to prove that prediction, adding: "We plan to conduct such research among non-hypertensive individuals."