CARDIA Study IDs 'Sobering' Rate of Hypertension in Blacks

Liam Davenport

July 18, 2018

Three quarters of black men and women develop hypertension by middle age, compared with just over half of white men and two fifths of white women, warn US researchers in a study that nevertheless underlined the role of following a healthy diet in preventing high blood pressure.

Data on over 3800 individuals from the Coronary Artery Risk Development in Young Adults (CARDIA) study showed that by age 55 years, the cumulative incidence of hypertension was approximately 75% in black men and women, compared with 55% in white men and 40% in white women.

Increased body mass index (BMI) and a parental history of hypertension were risk factors for developing hypertension, regardless of race or sex.

However, adherence to the Dietary Approaches to Stop Hypertension (DASH) diet, which is rich in fruits, vegetables, whole grains, fish, poultry, beans, seeds, and nuts, and low- or fat-free dairy foods, and limited in red meat and salt, was associated with a reduced risk for hypertension in both blacks and whites.

This would imply that lifestyle changes could be effective in reducing the excess risk for hypertension seen in blacks. However, lead author S. Justin Thomas, PhD, Department of Psychiatry, University of Alabama at Birmingham, pointed out that diet and exercise are probably not the only factors in play.

Speaking to theheart.org | Medscape Cardiology, he said that there is likely "a genetic component to the development of hypertension that may put blacks more at risk than whites," particularly given their finding "that even blacks at a young age with low blood pressure still have a higher risk than whites for hypertension."

The study, published in JAMA on July 11, used the 2017 American College of Cardiology (ACC)/American Heart Association (AHA) clinical practice guideline definition of hypertension of 130/80 mm Hg rather than the traditional threshold of 140/90 mm Hg.

Clyde Yancy, MD, Northwestern University in Chicago, Illinois, told theheart.org | Medscape Cardiology that the importance of the study is that it reveals the prevalence of hypertension, "especially in minorities, in the context of the newest guidelines."

Yancy, a former president of the AHA, added, "It is sobering to consider that 75% of black men and women will develop hypertension and will do so at an earlier age. This means that three out of every four African Americans is at risk for heart failure, kidney failure, and stroke."

He emphasized that early-onset hypertension is "of considerable public health importance" but that there are "very few" screening initiatives that include people aged under 30 years and that risk assessment scores are not calibrated for that population.

Despite concern "that the duration of exposure to high blood pressure increases the likelihood of end-organ disease," Yancy believes that the cost-effectiveness of screening in young adults "is likely not justifiable," thus underlying the need for "primordial prevention" to prevent the development of risk factors, such as hypertension.

He said, "Though not a strongly held concept in the broad space of prevention, in this case, preventing risk factors/diseases, ie, primordial prevention, vs treating risk factors/diseases to prevent overt cardiac events, ie, primary prevention, is the goal that carries some primacy now.

"To be clear, in this higher-risk group, it is better to prevent hypertension rather than prevent its consequences."

Yancy added: "It should be considered quite appropriate now to make very concerted public health efforts to prevent the onset of hypertension and thwart the negative influence of hypertension upstream in the life course and not once heart failure, chronic kidney disease, or stroke have occurred."

Evidence Gap

Previous cross-sectional studies using data from the National Health and Nutrition Examination Survey have consistently revealed a higher prevalence of hypertension in black individuals vs whites, beginning from childhood.

However, few studies have looked at the cumulative incidence of hypertension from young adulthood to middle age in black and whites, and even fewer have used the 2017 ACC/AHA blood pressure guideline to examine racial differences in hypertension.

The team therefore used data from the CARDIA study on 3890 blacks and whites aged 18 to 30 years from four US centers, none of whom had hypertension at enrollment. Participants underwent clinic visits at baseline and at 2, 5, 7, 10, 15, 20, 25, and 30 years following the baseline examination.

Defining hypertension as a mean systolic blood pressure of at least 130 mm Hg, mean diastolic blood pressure of at least 80 mm Hg, or self-reported use of antihypertensive medication, the team found that the cumulative incidence of hypertension by 55 years of age was 75.5% in black men and 75.7% in black women vs 54.5% in white men and 40.0% in white women.

After adjustment for age, sex, BMI, systolic and diastolic blood pressure, cigarette smoking, parental history of hypertension, education, physical fitness, serum uric acid levels, alcohol consumption, and adherence to the DASH diet, blacks had 1.5 to 2 times the risk of developing hypertension than whites within each baseline blood pressure category.

Specifically, the hazard ratio for incident hypertension among blacks vs whites was 1.97 for a baseline blood pressure less than 110/70 mm Hg, 1.80 for 110 to 119/70 to 74 mm Hg, and 1.59 for 120 to 129/75 to 79 mm Hg (P = .268 for interaction).

In both blacks and whites, parental history of hypertension, higher BMI, serum uric acid levels, and baseline blood pressure categories were associated with an increased risk for hypertension, while higher adherence to the DASH diet was linked to a lower risk.

In whites but not blacks, female sex and higher physical fitness levels were linked to a lower hypertension risk, while older age was associated with a greater hypertension risk in blacks but not whites.

Early, Comprehensive Action

Thomas said that changing lifestyle behaviors to prevent hypertension developing in the first place needs "to start at a very young age [and] I think we need to not just hit kids once or twice with the message that you need to eat well, get exercise, et cetera, but continue that throughout childhood."

He added, however, "Even if kids understand that, we run into the problem that their parents have to be onboard, and so we would want to involve the parents."

Thomas also pointed that, at least in Birmingham, Alabama, where part of the study was conducted, "blacks tend to be in a lower socioeconomic status background, and so they don't have the access to the foods that will allow them to follow the DASH diet."

He told theheart.org | Medscape Cardiology that "unfortunately it's a bit kind of bleak, but I think there's so many factors that you have to address.

"I think it's going to take more than just talking about but having a pretty comprehensive intervention to give people the means of being able to eat more healthily."

CARDIA was conducted and supported by the National Heart, Lung, and Blood Institute (NHLBI) in collaboration with the University of Alabama at Birmingham, Northwestern University, University of Minnesota, Kaiser Foundation Research Institute, and Johns Hopkins University School of Medicine. CARDIA is also partially supported by the Intramural Research Program of the National Institute on Aging (NIA) and an intra-agency agreement between NIA and NHLBI. The current analysis was supported by grants from the National Heart, Lung, and Blood Institute and a grant from the AHA. The authors declared no conflicts of interest.

JAMA. Published online July 11, 2018. Full text

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