Nov. 3, 2006 New research shows that higher levels of uric acid are strongly associated with high blood pressure in African Americans, suggesting that a simple blood test could predict risk and that treatments to lower uric acid may be a novel way to reduce hypertension-related complications in this population.
"The novel angle of our study is that the association between uric acid and hypertension is much stronger in blacks, a group that disproportionately suffers from kidney disease, stroke and other complications of hypertension," said Philip B. Mellen, M.D., M.S., assistant professor internal medicine, and lead investigator.
The results are reported online in Hypertension, a journal of the American Heart Association.
Uric acid levels are influenced by dietary factors, such as high levels of protein, and by the breakdown of the body's cells. Most uric acid is eliminated in urine. However, if excess uric acid is being produced or if the kidneys cannot remove enough of it, levels build up in the blood.
Very high levels of uric acid cause gout, but recent animal and human studies suggest that modest elevations of uric acid are one cause of hypertension. Currently, studies are under way to evaluate whether lowering uric acid prevents hypertension.
"If these studies show that lowering uric acid is an effective treatment, our research suggests that it may be especially appropriate for blacks," said Mellen.
Uric acid can be lowered by medications such as allopurinol and newer agents under development.
Previous studies have linked high levels of uric acid and hypertension, but they did not include a large number of blacks. For the current study, researchers evaluated data from the Atherosclerosis Risk in Communities study.
The 9,104 participants were free of hypertension when the study began. They were evaluated for hypertension at three-year intervals over four examinations. At the start, participants were between 45 and 64 with a mean age of 53 years.
A statistical analysis revealed that overall, uric acid levels in the highest quartile increased the risk of hypertension by about 15 percent. These results held true even after adjusting for other variables that could have affected results, such as age, baseline blood pressure, body mass index, kidney function, diabetes and smoking.
The link between uric acid and hypertension was particularly strong among black men. Black men in the highest quartile had a two-fold risk of developing hypertension, compared to black men in the lowest quartile. In black women in the highest quartile, the increase in risk was 30 percent, compared to black women in the lowest quartile.
"Uric acid in the blood was positively associated with hypertension over nine years of follow-up, and this relationship was stronger in blacks than in whites," said Mellen. "More research is warranted concerning the clinical consequences of high uric acid, especially in blacks."
Co-researchers were: Anthony J. Bleyer, M.D., M.S., Gregory W. Evans, M.S., Lynne E. Wagenknecht, DrPH, and David M. Herrington, M.D., M.H.S., all with Wake Forest, and Thomas P. Erlinger, M.D., M.P.H., with University of Texas Medical Branch, F. Javier Nieto, M.D., Ph.D., University of Wisconsin, and Marion R. Wofford, M.D., M.P.H., University of Mississippi Medical Center.
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