CARDIA: CRP may pose hypertension risk only in middle age

Caroline Cassels

February 17, 2006

Winston-Salem, NC - C-reactive protein may increase the risk of hypertension in middle-aged adults only and not their young counterparts, a new study suggests[1].

Designed to determine the antecedents and risk factors associated with cardiovascular disease in a group of young adults, this new analysis from the longitudinal Coronary Artery Risk Development in Young Adults (CARDIA) study showed no increased risk of hypertension associated with elevated CRP levels of >3 mg/L.

"In our young cohort, CRP concentration did not predict incident or prevalent hypertension after adjusting for BMI," the researchers, with first author Dr Susan G Lakoski (Wake Forest University School of Medicine, Winston-Salem, NC), write.

The study appears in the February 13, 2006 issue of the Archives of Internal Medicine.

The CARDIA study was launched in 1985 and includes 3919 African American and white men and women aged 18 to 30. Study subjects had CRP concentrations measured at year 7 of the study in 1992-1993 and again at year 15 (2000-2001). The authors report that in unadjusted analyses, study subjects with CRP concentrations of >3 mg/L had a 79% increased risk of incident hypertension compared with those with CRP levels of <1 mg/L. However, after adjusting for body mass index (BMI) and other potential confounders, they found no increased hypertension risk. Similarly, year-7 CRP concentration was not associated with changes to either diastolic or systolic blood pressure over an eight-year period. Results were similar across race- and sex-specific groups.

Unadjusted and adjusted hypertension risk associated with CRP >3 vs <1 mg/L

Risk type Relative risk CI (95%)
Unadjusted 1.79 1.40-2.28
Adjusted 1.14 0.86-1.53

According to the study, 18% of men vs 33% of young women had year-7 CRP levels >3 mg/L. Similarly, 33% of African Americans had year-7 CRP levels >3 mg/L compared with 20% of whites. Of those with diabetes, 45% had CRP concentrations in the highest category

Adults a different story

The authors point out there have been at least two large prospective studies that found baseline CRP levels predicted hypertension in older adults. The most notable of these, the Women ' s Health Study, showed that after adjustment for BMI and other potential confounders, baseline CRP remained a statistically significant predictor of hypertension among women with an average age of 50.

The reason CRP appears to increase hypertension risk in middle-aged and not young adults is not clear. However, say the authors, it is possible that "as a cohort ages, unknown variables in addition to obesity influence either blood pressure by an inflammatory mechanism or inflammation and blood pressure independently."

The authors called for further research to clarify the role of CRP in the etiology of hypertension and determine the effect of other factors, such as obesity, on this relationship.

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