BMI, Blood Pressure Strongly Linked Across Diverse Subgroups in China

The well-known link between body mass index (BMI) and blood pressure was further tightened last week, when a cross-sectional study of 1.7 million Chinese individuals showed the relationship is consistent across an array of more than 22,000 subgroups and apparent even at BMI levels that fall short of obesity.

Factors such as age, sex, ethnicity, occupation, household income, residency status, education, and geographic location made no difference, according to the findings published online in JAMA Network Open.

Previous analyses of the same data set, from the China PEACE Million Persons Project, captured the scope of hypertension in the rapidly changing nation. Fewer than half of those with high blood pressure even knew they had the condition. Only 30.1% of hypertensive individuals were taking BP-lowering drugs, with control achieved in just 7.2%.

For the latest study, the goal was to “characterize the relationship between BMI and blood pressure. The fact that this is a very strong relationship has been studied in the past,” lead author George C. Linderman, BS (Yale New Haven Hospital, CT), noted in an interview with TCTMD. “Going into this, we knew that there is this relationship. But what was not so clear was how [it] would change among different groups.”

If the association wasn’t consistently robust or linear, this might provide information on who best to target in public health campaigns or what physiologic forces might be at work, Linderman suggested. Instead, what they found is a consistent link across the population.

There was a divide, though, between individuals who did versus didn’t take antihypertensive drugs. “It suggests that not only does medication drop your blood pressure but perhaps it actually also can mitigate the effect of BMI on blood pressure,” Linderman explained, adding that if causal, this relationship is yet another reason to ensure patients are getting adequate medical therapy.

Overall, he said, the study is a reminder of “how important it is that public health measures are taken to address these obesity trends that we’re observing in China and other places around the world.”

China PEACE Million Persons Project

Linderman worked with senior author Harlan M. Krumholz, MD (Yale New Haven Hospital), and colleagues to analyze data on 1,727,411 adults (mean age 55.7 years; 59% women) who were seen at 141 primary care sites across all 31 provinces in mainland China between September 15, 2014, and June 20, 2017. Mean BMI was 24.7 kg/m2, while mean values for systolic BP and diastolic BP were 136.5 and 81.1 mm Hg, respectively. Fully 41.6% had hypertension, defined as systolic BP ≥ 140 mm Hg or diastolic BP ≥ 90 mm Hg), and more than four in 10 individuals were overweight or obese.

Between BMIs of 18.5 and 30.0 kg/m2, the association with blood pressure was positive and linear. On average, for every 1-kg/m2 increase in BMI, blood pressure rose by 1.3 mm Hg for men and 1.4 mm Hg for women. These increases parallel those found by earlier studies, Linderman and colleagues point out.

But among the various subgroup iterations in the latest research, only two stood out: individuals from the province of Tibet and those who were taking antihypertensive drugs. The investigators describe the association between BMI and BP in patients taking the medications as “substantially smaller” than the link in people with untreated hypertension.

The results have important implications for public health, they say. If mean BMI increases to 27.8 kg/m2 for men and 25.3 kg/m2 for women by the year 2025, this could potentially lead to more than 300,000 strokes and 350,000 cases of ischemic heart disease, according to their calculations. “It is a rough estimate but indicates the possibility that China will be facing an even larger challenge with hypertension in the future,” Linderman et al write.

“China and other countries experiencing an epidemiologic transition have two paths to mitigate the increasing threat to cardiovascular health posed by increasing BMI,” they continue. “The first is to slow the increase in BMI through public health interventions, and the second is through better treatment of hypertension. Although many public health strategies have not yet been successful in slowing the increase of BMI in adults, increasing the rates of treatment of hypertension is an attainable goal.”