MONDAY, Oct. 13 (HealthDay News) -- More Americans than ever are being treated for high blood pressure, say researchers from the U.S. National Heart, Lung, and Blood Institute.

The major factor in the dramatic increase in the number of Americans with high blood pressure appears to be the obesity epidemic rife in the United States, they noted.

"Additional efforts are needed to prevent hypertension from developing in the first place, with primary emphasis on prevention of obesity," said lead researcher Paul Sorlie, chief of the Epidemiology Branch in the institute's Division of Prevention and Population Sciences. "For those who have hypertension, additional efforts are needed to diagnose, treat and effectively control hypertension to reduce the adverse outcomes associated with hypertension."

The report was published in the November issue of Hypertension.

For the study, Sorlie's team collected data on a total of 30,781 people who participated in two National Health and Nutrition Examination surveys, one which ran from 1988 to 1994 and the other which covered 1999 to 2004.

The researchers found that between the two surveys, high blood pressure had increased in both men and women. For women, the increase started at age 40 and among men at age 60.

From 1994 to 2004, the percentage of Americans with high blood pressure increased from 50.3 percent to 55.5 percent. In addition, the number of people with prehypertension -- those likely to develop high blood pressure-- increased from 32.3 percent to 36.1 percent.

During the study period, 72 percent of those with high blood pressure knew they had it, and 61 percent were being treated, but only 35 percent had their blood pressure under control, Sorlie's group found.

The number of people who were aware of high blood pressure rose by 5 percent, particularly among black women. The treatment rates across race and gender also increased. Significant increases were seen among white men and black men and women, the researchers noted.

Moreover, the rate of those who had their blood pressure under control also increased. Among black men, blood pressure control rates increased, from 17 percent to 30 percent, and among white men it rose from 22 percent to 39 percent.

However, the number of white women with high blood pressure who had their blood pressure under control did not increase.

Of all groups, Mexican Americans had the lowest blood pressure control rates. This is especially true for young men (16 percent) and older women (19 percent), Sorlie's group found.

Sorlie thinks it is essential that people are aware of their blood pressure, and that those with high blood pressure work to get it under control.

"Know your blood pressure levels, seek appropriate treatment, and follow the guidance of your physician," Sorlie said. "But to prevent high blood pressure in the first place, develop and maintain a healthy lifestyle, and control your weight through exercise and health eating behaviors."

Dr. Theodore A. Kotchen, a professor of medicine and epidemiology at the Medical College of Wisconsin in Milwaukee, and author of accompanying journal editorial, said there is good news and bad news in the study.

"The good news about hypertension control in the U.S. is more people who have hypertension are aware of it, and more people who are aware of it are being treated, and more people being treated are being controlled," Kotchen said.

But despite the positive data, concerns about high blood pressure and obesity remain, Kotchen noted. "Heart disease and stroke remain leading causes of death, and hypertension is a major risk factor for cardiovascular disease and stroke," he said.

"The percentage of hypertension is increasing, and perhaps that's due to obesity. We need to pay more attention to the problem of obesity and overweight," Kotchen said. "Hypertension remains uncontrolled in an unacceptably large number of individuals. We've made some progress, but more work needs to be done."

More information

For more on high blood pressure, visit the American Heart Association.