THURSDAY, Sept. 24, 2009 (HealthDay News) -- America's sweet tooth may be contributing to the ever-increasing number of people with high blood pressure.
Two new studies link fructose, the kind of sugar in soft drinks and many sweetened foods, to high blood pressure, which is a major risk factor for heart attack, stroke and other cardiovascular diseases.
"It raises the possibility that fructose may have a role in the pathogenesis of hypertension," said Dr. Richard J. Johnson, professor and head of the division of renal diseases and hypertension at the University of Colorado and a co-author of one of the studies. Both were scheduled to be presented this week at an American Heart Association conference in Chicago on blood pressure research.
"It shows that if you ingest a certain amount of fructose, you can raise blood pressure" to the level of hypertension, Johnson said.
Fructose makes up about half of ordinary table sugar; the other half is glucose. Fructose is widely used by food and beverage manufacturers because it is inexpensive. "Americans are eating large amounts of this, three or four times more than we did 50 years ago," Johnson said.
The study, led by Johnson and Dr. Santos Perez-Pozo, a nephrologist at Mateo Orfila Hospital in Minorca, Spain, included 74 men, average age 51, who ate a diet that included 200 grams of fructose a day. That is far more than the average U.S. consumption of 50 to 70 grams, but "some people are getting as much as 150 grams a day, so we are not that far off," Johnson said.
Half the men also took daily doses of allopurinol, a drug for gout that reduces blood levels of uric acid, and the others took a placebo, an inactive substance.
After two weeks, men on the high-fructose diet who were taking the placebo had an average increase of six points in systolic blood pressure (the first number in a reading of, for instance, 120/80) and three points in diastolic blood pressure (the second number). The men taking allopurinol along with their high-fructose diet had only a one-point increase in systolic pressure.
The study results appear to confirm the belief that fructose raises blood pressure by increasing uric acid levels, Johnson said, but he stressed that the finding is preliminary.
"Clearly we need additional trials," he said. "We need larger population-based trials to see if there is a causal relationship."
In the United States, one in three adults has high blood pressure, which was the cause of death or a contributing factor in about 319,000 U.S. deaths in 2005, according to the heart association.
The second study scheduled for presentation at the heart meeting found that the timing as well as the amount of fructose that's consumed affected blood pressure. The study was done on mice.
For the study, the mice, who slept during the day, had either unrestricted access to fructose-enriched water or access restricted to either daytime or nighttime hours. Monitors were implanted in the mice to measure their blood pressure.
All the mice consumed large amounts of the sweetened water, said Mariana Morris, assistant vice president for graduate studies and chairwoman of the pharmacology and toxicology department at Wright State University's Boonshoft School of Medicine in Dayton, Ohio, who led the experiment.
The mice that consumed fructose continuously or at night had an increase in blood pressure, with a spike at night, when they were awake. The pattern was reversed in mice that consumed fructose in the daylight hours -- high during the day and low at night. The reversal in the day-night rhythm "is similar to the pattern seen in human diabetics," Morris said. This suggests that the timing of fructose intake is important in cardiovascular pathologies, she said.
All of the mice gained weight. "If you give them fructose at the wrong time, when they are supposed to be sleeping, it has a greater pathological effect on blood pressure and body weight," Morris said. "But they love it, no matter when they get it."
The results paralleled those of a study reported Sept. 3 online in Obesity in which mice were put on a high-fat diet. Some were fed during their normal daytime sleeping hours, and others were fed at night. The mice that ate during the day (when they were supposed to be sleeping) averaged a 48 percent weight gain, compared with 20 percent for those fed at night.
What happens in mice probably happens in people, Morris said. "We have 99 percent of the same genome," she said.
The U.S. National Heart, Lung and Blood Institute has more on high blood pressure .