Body Mass Index and Mortality Among Adults With Incident Myocardial Infarction

Laila Al-Shaar; Yanping Li; Eric B. Rimm; JoAnn E. Manson; Bernard Rosner; Frank B. Hu; Meir J. Stampfer; Walter C. Willett

Disclosures

Am J Epidemiol. 2021;190(10):2019-2028. 

In This Article

Abstract and Introduction

Abstract

The relationship between body mass index (BMI; weight (kg)/height (m)2) and mortality among survivors of myocardial infarction (MI) remains controversial. We examined the relationships of BMI before and after MI and change in weight with all-cause mortality among participants in the Nurses' Health Study (1980–2016) and Health Professionals Follow-up Study (1988–2016) cohorts. During a follow-up period of up to 36 years, we documented 4,856 participants with incident nonfatal MI, among whom 2,407 died during follow-up. For pre-MI and post-MI BMI, overweight was not associated with lower mortality. Obesity (BMI ≥30) was associated with higher risk of mortality. Compared with participants with post-MI BMI of 22.5–24.9, hazard ratios were 1.16 (95% confidence interval (CI): 1.01, 1.34) for BMI 30.0–34.9 and 1.52 (95% CI: 1.27, 1.83) for BMI ≥35.0 (P for trend < 0.001). Compared with stable weight from before MI to after MI, a reduction of more than 4 BMI units was associated with increased mortality (hazard ratio = 1.53, 95%: CI: 1.28, 1.83). This increase was seen only among participants who lost weight without improving their physical activity or diet. Our findings showed no survival benefit of excess adiposity in relation to risk of mortality. Weight loss from before to after MI without lifestyle improvement may reflect reverse causation and disease severity.

Introduction

Obesity affects about 40% of the US adult population[1] and is a major contributor to premature morbidity and mortality.[2] An apparent survival benefit, termed the obesity paradox, has been described among overweight and obese patients with heart failure,[3] myocardial infarction (MI),[4] hypertension,[5] type 2 diabetes,[6] and end-stage renal disease.[3] However, most prior studies have been limited by small sample sizes,[7] short follow-up,[7–10] lack of information on intentionality of weight change,[11] or incomplete adjustment for diet, physical activity, and smoking.[4,7,8] Potential incomplete control for preexisting health conditions and disease severity[12] raise additional concerns about reverse causation bias, whereby weight loss due to underlying illness can affect the relationship between weight and mortality.[12–14]

In an attempt to mitigate those limitations, we conducted a detailed analysis to evaluate the relationship of body mass index (BMI; weight (kg)/height (m)2), measured before and after MI diagnosis, with long-term mortality among survivors of MI among participants in 2 large prospective US cohort studies.[9] We had previously demonstrated a strong positive monotonic association between BMI and incidence of MI in these cohorts.[15]

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