Post-MI mortality is significantly lower among those with an above normal BMI yet much higher for individuals when their BMI is below normal
The post-myocardial infarction (post-MI) mortality risk has been found to be significantly lower among those who are classed as overweight or obese yet much higher for those with a body mass index (BMI) below the ideal range.
This was the conclusion of a systematic review and meta-analysis by an international team led by researchers from Aberdeen University, Scotland, UK.
Body mass index (BMI) is a measure of nutritional status in adults and defined as a person’s weight in kilograms divided by the square of the person’s height in metres (kg/m2). Based on the BMI, individuals are deemed to be of normal weight when their BMI is being 18.5 and 24.9.
According to the World Health Organization, individuals with a BMI > 25 are classed as overweight, and obese when their BMI is equal to or > 30). According to the American Heart Association, the presence of obesity leads to the development of cardiovascular disease and mortality, independently of other cardiovascular risk factors.
Despite this, meta-analyses support a J-shaped relationship between mortality and BMI in patients with coronary artery disease, i.e., the risk is highest for underweight and overweight individuals and lowest for those with a normal BMI.
Nevertheless, whether this same J-shaped relationship holds for post-MI mortality is unknown and was subject of the present meta-analysis. The researchers looked for studies in adults with a previous myocardial infarction where the BMI had been measured and which reported on outcomes such as all-cause mortality, recurrence of an adverse cardiovascular event or hospital re-admission.
Hazard ratios (HRs) were used to assess the risk of mortality and the normal BMI (18.5 – 24.9) was used as the reference range for comparative purposes.
Post-MI mortality and BMI
A total of 27 articles with 308,430 participants and with follow-up periods ranging from 6 months to 17 years were included in the analysis.
Among individuals who were classed as overweight (BMI 25 – 29.9) compared to those of normal BMI and based on 8 studies, there as a 15% lower risk of post-MI mortality (HR = 0.85, 95% CI 0.76 – 0.94, p = 0.002).
In 14 studies that reported on odds ratios (ORs) rather than hazard ratios, there was also a reduced mortality risk (OR = 0.72, 95% CI 0.64 – 0.81, p < 0.0001).
Among obese patients (BMI > 30) the HR was 0.86 (95% CI 0.81 – 0.91, p < 0.0001) and for morbidly obese patients, although the HR was reduced, it was not statistically significant (HR = 0.89, 95% CI 0.78 – 1.01, p = 0.08).
In contrast, among those with a BMI < 18.5, there was a 42% higher risk of post-MI mortality (HR = 1.42, 95% CI 1.25 – 1.62, p < 0.0001) and again, where studies reported odds ratios, this was also significantly increased (OR = 2.48, 95% CI 1.77 – 3.47, p < 0.0001).
There were no significant effects when comparing the risk of hospital re-admission for those who were overweight, obese and underweight.
The authors concluded that individuals who have a BMI less than the normal range are at a significantly higher risk of post-MI mortality. They called for future studies to examine the prognostic utility of other markers of nutritional status in MI to better identify those at a higher risk of poor clinical outcomes.
Citation
De Paola L et al. Body Mass Index and Mortality, Recurrence and Readmission after Myocardial Infarction: Systematic Review and Meta-Analysis J Clin Med 2022
