Middle-aged men who took part in the study showed significant increases in blood pressure after eating a high-sugar diet for just two weeks unless they took the drug allopurinol, used to treat the painful inflammatory condition known as gout.
Researcher Richard Johnson, MD, and colleagues first showed that allopurinol could lower high blood pressure by lowering uric acid levels in a small study involving hypertensive preteens and teens reported last year.
Their newly published research showed the same thing in adult men, but Johnson tells WebMD that more study is needed to confirm the findings.
"This is the first direct study to suggest that fructose can raise blood pressure and that it is mediated by uric acid, but it is a pilot study," he says. "Allopurinol does have rare, but potentially serious, side effects. Clearly, we need more research before this drug can be recommended to lower blood pressure."
Fructose, Uric Acid, and Blood Pressure
The study included 74 middle-age men whose average age was 51. All of the men ate 200 grams (800 calories) of fructose every day for two weeks in addition to their regular diets.
To put this in perspective, a recent national health survey suggests that added sugars account for about 400 calories consumed by the average American each day.
Almost all of the sugars and syrups used to sweeten processed foods contain roughly equal amounts of fructose and another sugar, glucose.
Table sugar is made up of about 50% fructose and 50% glucose, while high-fructose corn syrup is 55% fructose and 45% glucose.
All the men in the study ate the high-fructose diets, but half also took the gout drug.
After two weeks on the high-sugar diet, the men who took the drug showed significant declines in uric acid levels and no significant increase in blood pressure.
In contrast, men who did not take the drug had increases of about 6 points in systolic blood pressure (the top blood pressure number) and 3 points in diastolic blood pressure (the bottom blood pressure number).
American Heart Association Recommendations
While it is too soon to recommend taking uric acid-lowering drugs to lower blood pressure, it is clear that too much sugar in the diet can hurt the heart, Johnson says.
The American Heart Association reached the same conclusion in guidelines published last month.
The group recommends that:
- Women eat no more than 25 grams (100 calories) of added sugar per day, which is equivalent to about six teaspoons.
- Men should eat no more than 37.5 grams (150 calories) of added sugar, which is equivalent to nine teaspoons.
- Foods high in added sugars should not take the place of foods that contain essential nutrients.
"Sugar has no nutritional value other than to provide calories," University of Vermont professor of nutrition Rachel K. Johnson, PhD, MPH, notes in a written statement.
She adds that soft drinks and other sugar-sweetened beverages are the No.1 source of added sugar in the typical American's diet.
American Heart Association spokeswoman Rhian M. Touyz, MD, PhD, of the University of Ottawa, characterized the new research linking fructose to high blood pressure as intriguing but not conclusive in an interview with WebMD.
"It is clear that we need larger studies to confirm this association," she says. "We know that eating lots of sugar contributes to obesity, but we can't say with certainty that it has a direct impact on blood pressure."