Higher BMI in Young Adults 'Likely to Cause' High BP, Enlarged Heart

Marlene Busko

August 09, 2018

Higher body mass index (BMI) is "likely to cause" higher blood pressure and higher left ventricular mass index, researchers conclude from a new study.

The investigators analyzed data from participants in the ongoing Avon Longitudinal Study of Parents and Children (ALSPAC) study, also known as the Children of the 90s. In a large sample of 17-year-old participants, using Mendelian randomization, the researchers determined that participants who had a higher BMI also had a higher blood pressure and a higher left ventricular mass index.

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Next, in a recall-by-genotype analysis of other study participants when they were 21 years old, the researchers found that those who had a higher BMI also had higher blood pressure and a higher left ventricular mass as well as a higher cardiac output and stroke volume.

"At 17, we found that BMI was potentially causally influencing blood pressure and left ventricular mass index, which means that already at age 17 there's a potentially detrimental effect on the heart," lead author Kaitlin H. Wade, PhD, from the University of Bristol, United Kingdom, told theheart.org | Medscape Cardiology in an interview.

"No one's really looked at this in such a large sample of children, especially in terms of causal assessment," she added. "So far, it's all been just associational linking using observational data."

"Mendelian randomization mimics a randomized controlled trial," Wade added. That is, in a large population, there is a huge amount of random genetic variation, where some individuals will have a genetic predisposition to having an ever so slightly higher BMI than others, for example.

"This genetic predisposition is independent of confounders, such as diet and lifestyle," she added. "So, this allows researchers to assess whether a higher BMI may cause higher blood pressure, for example, as opposed to simply being associated with it."   

"Our results," the researchers conclude, "support efforts to reduce BMI from a young age to prevent the development of precursors of long-term adverse cardiovascular health."

According to Wade, this work also stresses that "it's never too early to start reducing BMI to a normal healthy level...especially given that obesity is widely prevalent, and the population average of the number of obese children is increasing."

The findings were published online July 31 in Circulation.

Higher BMI, Effect on Young Hearts

Studies in adults have shown "quite convincingly" that higher BMI likely increases the risk for cardiovascular disease or mortality from cardiovascular disease, Wade noted, but it is not clear if high BMI in young adults already has a detrimental effect on markers of cardiovascular health.

To investigate this, the researchers analyzed data from ALSPAC, which has been collecting clinical, questionnaire, and biological data from parents and offspring in Bristol since the children were born in 1991 to 1992. The children are now around 26 years old.

In the first part of the study, the researchers performed a Mendelian randomization analysis of 3000 participants in ALSPAC, when they were 17 years old.

Wade and colleagues determined the participants' genetic risk score for BMI, based on 97 single-nucleotide polymorphisms that are associated with BMI according to a previously published article in Nature.

They used this genetic risk score as a proxy for BMI to examine how BMI was associated with blood pressure, carotid-femoral pulse wave velocity, carotid intima-media thickness, and left ventricular mass index from echocardiography in 1420 to 3108 individuals for different outcomes.  

They found that participants with a higher BMI had higher systolic and diastolic blood pressures, pulse pressure, mean arterial pressure, and left ventricular mass index.

In the second part of the study, the recall-by-genotype analysis, the researchers recalled 418 ALSPAC participants, who were 21 years old at the time, from the lower and upper 30% of the distribution of a genetic risk score for BMI.

In this subset, 191 individuals had a genetic predisposition to a lower BMI (and had a mean BMI of 22.6 kg/m2) and 227 had a genetic predisposition to a higher BMI (and had a mean BMI of 26.2 kg/m2).  

Individuals with a genetic predisposition to a higher BMI had higher blood pressure and a higher MRI-derived left ventricular mass index (as in the first part of the study), and they also had a higher cardiac output and stroke volume, also measured with MRI.

Neither of the two analyses suggested that BMI causes a change in heart rate, carotid intima-media thickness, or carotid-femoral pulse wave velocity, as has been seen in previous studies showing such an association. 

"The main message of the study," Wade said, "is that any reduction in BMI to a normal, healthy range from a young age is likely to prevent later cardiovascular disease."

The UK Medical Research Council and the Wellcome Trust and the University of Bristol provide core support for ALSPAC. Genome-wide association study data were generated by Sample Logistics and Genotyping facilities at Wellcome Sanger Institute and LabCorp using support from 23andMe. The authors have disclosed no relevant financial relationships.  

Circulation. Published July 30, 2018. Abstract   

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