The findings are published as a paper in the October 13 issue of Hypertension: Journal of the American Heart Association, and were the work of researchers at the the National Heart, Lung, and Blood Institute (NHLBI), of the National Institutes of Health, based in Bethesda, Maryland.
Lead author dr Jeffrey A Cutler, who is a consultant to NHLBI's Divisions of Prevention and Population Sciences and Cardiovascular Diseases, said their findings confirmed:
"What others have observed based on more limited data and what one would expect, because obesity is an important cause of high blood pressure."
For the study, Cutler and colleagues compared data from two similar surveys taken roughly ten years apart. The first set of data came from the third National Health and Nutrition Examination Survey (NHANES III), which ran from 1988-1994, and the second set of figures came from the first six years (covering 1999 to 2004) of the current NHANES, which collects data continuously in blocks of two years.
This gave them a total data set covering 16,351 adult participants (aged 18 and over) from the first survey and 14,430 from the second survey.
After standardizing the figures according to age, the results showed the overall prevalence of high blood pressure rose from 24.4 to 28.9 per cent over the ten years or so between the two sets of figures.
The investigators defined prevalence as an "estimate of the total number of cases of a disease existing in a population during a specified period"; expressed as a percentage of the population.
The results also showed that being overweight explained part but not all of the increase in high blood pressure across all age and ethnic/race groups.
Study co-author Dr Paul D. Sorlie, who is Epidemiology Branch Chief in the Division of Prevention and Population Sciences at the NHLBI said:
"We see that much of the magnitude in men is accounted for by obesity, but less so in women, possibly because of some unexplored changes in risk factors for hypertension."
The results also showed that:
- The most notable change in most gender and race groups was a reduction in the percentage of American adults in the population who have normal blood pressure (from 55.5 to 50.3 per cent): due to the rise of prevalence in all high blood pressure categories.
- The percentage of the population estimated to be prehypertensive (between 120 and under 140 systolic, and/or 80 to 89 diastolic) went up from 32.3 to 36.1 per cent.
- Awareness of having high blood pressure went up by more than 5 per cent among men, and it also went up among non-Hispanic black women.
- During 1999 to 2004, 72 per cent of American adults with high blood pressure were aware of it, 61 per cent were being treated and 35 per cent were keeping it under control.
- Treatment rates also went up in all race and gender groups.
- All race and gender groups also showed a tendency to improve their control of blood pressure, with non-Hispanic white and black men showing the highest increases, from 22 to 39 per cent and from 17 to 30 per cent respectively between the two surveys.
- One group that failed to show any significant improvement between the two surveys in their control of blood pressure was white women .
- Mexican Americans appear to have the lowest proportion of adults in control of their blood pressure, especially among young men (16 per cent) and older women (19 per cent).
Cutler commented that while there has been a considerable improvement in the treatment and control of high blood pressure, it is "far from ideal", and:
"Most importantly, we have to do a better job of prevention."
He also said that the gender pattern appears to have reversed over the decade or so covered by the two surveys, with white men now able to control their blood pressure as well as if not better than white women.
Dr Theodore A. Kotchen, Professor of Medicine and Epidemiology, Associate Dean for Clinical Research, Medical College of Wisconsin in Milwaukee said in an accompanying editorial that from an overall and a patient care perspective, the study emphasizes the importance of:
"Preventing obesity and encouraging weight loss for the overweight as strategies for hypertension prevention."
He said this was particularly relevant because the past decade has seen a several fold increase in childhood obesity.
"In 2003-2006, 16.3 percent of children and adolescents were at or above the 95th percentile of BMI [body mass index] for age, based on the 2000 Centers for Disease Control and Prevention growth charts," said Kotchen.
"Trends in Hypertension Prevalence, Awareness, Treatment, and Control Rates in United States Adults Between 1988-1994 and 1999-2004."
Jeffrey A. Cutler, Paul D. Sorlie, Michael Wolz, Thomas Thom, Larry E. Fields, and Edward J. Roccella.
Hypertension, Published Online on October 13, 2008.
Click here for Abstract.
Source: AHA, journal abstract.