Structural Bias in Studies of Cardiovascular Disease: Let's Not Be Fooled by the "Obesity Paradox"

Cardiovascular Risk and Diseases in Patients With and Without Leptin-Melanocortin Pathway Variants

OBJECTIVE

To study differences in cardiovascular risk factors and diseases between patients with and without genetic variants in the leptin-melanocortin pathway.

METHODS

A cross-sectional study of patients with a history of severe obesity genotyped in June 2019 as participants of the Mayo Clinic Biobank was conducted in March 2022 to assess differences in cardiovascular risk and diseases between carriers of a heterozygous variant in the leptin-melanocortin pathway and noncarriers. Cardiovascular risk factors included hypertension, diabetes, dyslipidemia, and smoking. Cardiovascular disease includes coronary artery disease, peripheral artery disease, and cerebrovascular accidents. Patients with a history of bariatric surgery were excluded. We used logistic regression models to estimate the odds ratio and 95% CI, adjusting for age, body mass index (BMI), and sex.

RESULTS

Among a total of 168 carriers (8%; 121 [72%] female; mean [SD] age, 65.1 [14.9] years; BMI, 44.0 [7.4] kg/m2) and 2039 noncarriers (92%; 1446 [71%] female; mean [SD] age, 64.9 [14.4] years; BMI, 42.9 [6.6] kg/m2), carriers had higher prevalence odds of hypertension (odds ratio, 3.26; 95% CI, 2.31 to 4.61; P<.001) and reported higher number of cardiovascular risk factors compared with noncarriers (2.4 [1.1] vs 2.0 [1.1]; P<.001). There were no significant differences in the adjusted odds associated with diabetes, dyslipidemia, smoking, or cardiovascular disease.

CONCLUSION

Despite having similar body weight and BMI, carriers of heterozygous variants in the leptin-melanocortin pathway had higher rates of hypertension than noncarriers. These findings point to an association between hypertension and leptin-melanocortin pathway variants.

Repercussions of absolute and time-rated BMI "yo-yo" fluctuations on cardiovascular stress-related morbidities within the vascular-metabolic CUN cohort

Aims

The association between body mass index (BMI) fluctuation and BMI fluctuation rate with cardiovascular stress morbidities in a Caucasian European cohort was evaluated to ascertain the impact of weight cycling.

Methods

A total of 4,312 patients of the Vascular-Metabolic CUN cohort (VMCUN cohort) were examined and followed up during 9.35 years ( ± 4.39). Cox proportional hazard ratio analyses were performed to assess the risk of developing cardiovascular stress-related diseases (CVDs) across quartiles of BMI fluctuation, measured as the average successive variability (ASV) (ASV = |BMIt0 - BMIt1| + |BMIt1 - BMIt2| + |BMIt2-BMIt3| +…+ |BMItn - 1 - BMItn|/n - 1), and quartiles of BMI fluctuation rate (ASV/year).

Results

There were 436 incident cases of CVD-associated events involving 40,323.32 person-years of follow-up. A progressively increased risk of CVD in subjects with greater ASV levels was found. Also, a higher level of ASV/year was significantly associated with an increased risk of developing CVD stress independent of confounding factors with a value of 3.71 (95% CI: 2.71-5.07) for those in the highest quartile and 1.82 (95% CI: 1.33-2.50) for those in the third quartile.

Conclusions

The BMI fluctuation rate seems to be a better predictor than BMI fluctuation of the potential development of cardiovascular stress morbidities. The time-rated weight fluctuations are apparently more determinant in increasing the risk of a CVD than the weight fluctuation itself, which is remarkable in subjects under "yo-yo" weight patterns for precision medicine.

Survival bias may explain the appearance of the obesity paradox in hip fracture patients

Patients with low-energy hip fractures do not follow the obesity paradox as previously reported. In datasets where injury mechanism is not available, the use of age >50 years (as opposed to commonly used >65 years) as a surrogate for a low-energy hip fracture patients may be a more robust inclusion criterion.  PURPOSE: In elderly patients with a hip fracture, limited data suggests that obese patients counterintuitively have improved survival compared to normal-weight patients. This "obesity paradox" may be the byproduct of selection bias. We hypothesized that the obesity paradox would not apply to elderly hip fracture patients.

METHODS

The National Surgical Quality Improvement Project dataset identified 71,685 hip fracture patients ≥50 years-of-age with complete body mass index (BMI) data that underwent surgery. Patients were stratified into under and over 75-year-old cohorts (n=18,956 and 52,729, respectively). Within each age group, patients were stratified by BMI class and compared with respect to preoperative characteristics and 30-day mortality. Significant univariate characteristics (p<0.1) were included in multivariate analysis to determine the independent effect of obesity class on 30-day mortality (p<0.05).

RESULTS

Multivariate analysis of <75-year-old patients with class-III obesity were more likely to die within 30-days than similarly aged normal-weight patients (OR 1.91, CI 1.06-3.42, p=0.030). Multivariate analysis of ≥75-year-old overweight (OR 0.69, CI 0.62-0.77, p<0.001), class-I obese (OR 0.62, CI 0.51-0.74, p<0.001), or class-II obese (OR=0.69, CI 0.50-0.95, p=0.022) patients were less likely to die within 30-days when compared to similarly aged normal-weight patients.

CONCLUSIONS

Our data suggest that obesity is a risk factor for mortality in low-energy hip fracture patients, but the appearance of the "obesity paradox" in elderly hip fracture patients results from statistical bias that is only evident upon subgroup analysis.

Inverse association of mortality and body mass index in patients with left ventricular systolic dysfunction of both ischemic and non-ischemic etiologies

BACKGROUND

Obesity is a worldwide epidemic that has been associated with poor outcomes. Previous studies have demonstrated an inverse relationship between body mass index (BMI) and outcomes, the 'obesity paradox', in several diseases.

HYPOTHESIS

We sought to evaluate whether the obesity paradox is present in patients with left ventricular systolic dysfunction (LVSD) of all etiologies, using all-cause mortality as the primary endpoint and hospitalization as the secondary endpoint.

METHODS

We conducted a retrospective cohort study of LVSD patients (n = 18 003) seen within the University of Pittsburgh Medical Center network between January 2011 and December 2017. Patients were divided into four BMI categories (underweight, normal weight, overweight, and obese) and stratified by left ventricular ejection fraction (LVEF): <20%, 20-35%, and 35-50%.

RESULTS

Over a median follow-up of 2.28 years, higher BMI (mean 28.9 ± 6.8) was associated with better survival for the overall cohort and within LVEF strata (p < .0001). The most common cause of hospitalization was subendocardial infarction among underweight and normal weight patients and heart failure among overweight and obese patients. Cox proportional hazards model showed that BMI, age, and comorbid conditions of diabetes mellitus, chronic obstructive pulmonary disease, chronic kidney disease, and prior myocardial infarction are independent predictors of death.

CONCLUSIONS

Our results support the existence of an obesity paradox impacting all-cause mortality in patients with LVSD of ischemic and non-ischemic etiologies even after adjusting for LVEF and comorbidities. Additional research is needed to understand the effect of weight loss on survival once a diagnosis of LVSD is established.

Differential predictive factors for cardiovascular events in patients with or without cancer history

Although attention has been paid to the relationship between malignant diseases and cardiovascular diseases, few data have been reported. Moreover, there have also been few reports in which the preventive factors were examined in patients with or without malignant disease histories requiring percutaneous coronary intervention (PCI).This was a retrospective, single-center, observational study. A total of 1003 post-PCI patients were divided into a malignant group, with current or past malignant disease, and a nonmalignant group. The primary endpoint was a composite of cardiovascular death, nonfatal myocardial infarction, stroke, revascularization, and admission due to heart failure within 5 years of PCI. Kaplan-Meier analysis showed a significantly higher probability of the primary endpoint in the malignant group (P = .002). Multivariable Cox hazard analyses showed that in patients without a history of malignant, body mass index (BMI) and the presence of dyslipidemia were independent and significant negative predictors of the primary endpoint (BMI: hazard ratio [HR] 0.73, 95% confidence interval [CI] 0.53-0.99, P = .041; prevalence of dyslipidemia: HR 0.72, 95% CI 0.52-0.99, P = .048), and the presence of multi-vessel disease (MVD) and the prevalence of peripheral artery disease (PAD) were independent and significant positive predictors of the primary endpoint (prevalence of MVD: HR 1.68, 95% CI 1.18-2.40, P = .004; prevalence of PAD: HR 1.51, 95% CI 1.03-2.21, P = .034). In patients with histories of malignancy, no significant independent predictive factors were identified.Patients undergoing PCI with malignancy had significantly higher rates of adverse cardiovascular events but might not have the conventional prognostic factors.

Body mass index and all-cause mortality in patients with atrial fibrillation: insights from the China atrial fibrillation registry study

BACKGROUND

Impact of body mass index (BMI) on all-cause mortality in atrial fibrillation (AF) patients remains controversial.

METHODS

A total of 10,942 AF patients were prospectively enrolled and categorized into four BMI groups: underweight (BMI < 18.5 kg/m²), normal weight (BMI 18.5-24 kg/m²), overweight (BMI 24-28 kg/m²) and obesity (BMI ≥ 28 kg/m²). The primary outcome was all-cause mortality. Different Cox proportional hazards models were performed to evaluate the association between BMI and all-cause mortality.

RESULTS

During a median follow-up of 30 months (IQR 18-48 months), 862 deaths events occurred. Compared to normal BMI, higher BMI was associated with a lower mortality risk (overweight: HR 0.70; 95% CI 0.61-0.81, P < 0.0001 and obesity: HR 0.54; 95% CI 0.44-0.67, P < 0.0001) and lower BMI was associated with a higher mortality risk (HR 2.23, 95% CI 1.67-2.97, P < 0.0001).

CONCLUSION

A reversed relationship between BMI and all-cause mortality in AF patients was found. Higher risk of mortality was observed in underweight patients compared to patients with a normal BMI, while overweight and obese patients had a lower risk of all-cause mortality.

CLINICAL TRIAL REGISTRATION

URL: http://www.chictr.org.cn/showproj.aspx?proj=5831. Unique identifier: ChiCTR-OCH-13003729.

Impact of body fat distribution on long-term clinical outcomes after drug-eluting stent implantation

Background and objective

The distribution of body fat is closely related to cardiovascular disease and outcomes, although its impact on patient prognosis after percutaneous coronary intervention (PCI) with drug-eluting stent (DES) has not been evaluated. We investigated the impact of truncal fat distribution on long-term clinical outcomes after DES treatment.

Methods

In 441 DES-treated patients, dual energy X-ray absorptiometry was performed to assess total and regional body fat distribution after index PCI. The ratio of truncal fat to total body fat mass (%FM_trunk/FM_total) was calculated as a representative parameter for truncal fat distribution. The primary endpoint was major adverse cardiac events (MACE), a composite of ischemia-driven target vessel revascularization (TVR), non-procedural myocardial infarction, cardiac death at 5 years.

Results

During the median follow-up duration of 1780 days, MACE occurred in 22.0% of patients, with the highest-quartile group of %FM_trunk/FM_total having a higher rate than the lowest quartile group (27.8% vs. 15.3%; log rank p = 0.026). The difference was driven by a higher rate of ischemia-driven TVR (25.9% vs. 9.9%; log rank p = 0.008). In multivariable Cox regression analyses, %FM_trunk/FM_total was independently associated with MACE (hazard ratio: 1.075; 95% CI: 1.022–1.131; p = 0.005), but body mass index (BMI) was not.

Conclusions

In DES-treated patients, truncal fat distribution is associated with unfavorable clinical outcomes and is more clinically relevant than BMI.

Body Mass Index of 92,027 patients acutely admitted to general hospitals in Denmark: Associated clinical characteristics and 30-day mortality

BACKGROUND

Data are sparse on the range of BMI among patients acutely admitted to general hospitals. We investigated BMI values and associated patient characteristics, reasons for hospital admission, and mortality in Denmark.

METHODS

We identified all persons with an acute inpatient admission 2011-2014 in Central Denmark Region and assessed BMI measurements recorded in the Clinical Information System. We used cross-sectional and cohort analyses to examine the BMI distribution and its association with demographic characteristics, comorbidities, medication use, tobacco smoking, reasons for admission, and 30-day mortality.

RESULTS

Among 92,027 acutely admitted patients (median age 62 years, 49% female) with a BMI measurement, 4% had a BMI (kg/m2) <18.5, 42% a BMI between 18.5 and 25, 34% a BMI between 25 and 30, and 20% a BMI ≥30. Compared with normal-weight patients, 30-day mortality was high among patients with BMI <18.5 (7.5% vs. 2.8%, age- and smoking-adjusted odds ratio (aOR) 2.4; 95% confidence interval (CI): 2.0-2.9, whereas patients with overweight (aOR 0.7; 95% CI: 0.6-0.8) and obesity class I (aOR 0.8; 95% CI: 0.6-0.9)). Compared with the total population, patients with BMI <18.5 were older (68 years median); more were female (73%); more had comorbidities (Charlson Comorbidity Index score >0 in 42% vs. 33% overall), more were current smokers (45% vs. 27% overall), and acute admissions due to respiratory diseases or femoral fractures were frequent. In contrast, patients with BMI ≥30 were relatively young (59 years median), fewer smoked (24%): type 2 diabetes, sleep disorders, cholelithiasis, and heart failure were frequent diagnoses. Prevalence of therapies for metabolic syndrome, pain, and psychiatric disorders increased with higher BMI, while patients with BMI <18.5 frequently used asthma medications, glucocorticoids, and antibiotics.

CONCLUSION

In patients acutely admitted to general hospitals, reasons for hospital admission and associated clinical characteristics differ substantially according to BMI range. BMI <18.5 is a clinical predictor of high short-term mortality.

Paediatric obesity appears to lower the risk of diabetes if selection bias is ignored

BACKGROUND

Frustrated with the onslaught of articles reporting fascination with results that appear paradoxical but are merely due to selection bias, we studied the apparent effect of obesity on diabetes risk in youth who had a test for diabetes. We hypothesised that obese subjects would have lower rates of diabetes than non-obese subjects due to selection bias, and consequently, obesity would appear to lower the risk of diabetes.

METHODS

Retrospective cohort study of children (4-9 years), pre-teens (10-12 years) and teenagers (13-19 years). Participation was restricted to those who had a test of haemoglobin A1C along with measured height and weight. Body mass index percentile via the Centers for Disease Control and Prevention age and sex standards was calculated and categorised. The main outcome was A1C%, subsequently categorised at the level for diagnosis of diabetes mellitus (≥6.5%).

RESULTS

The sample consisted of 134 (2%) underweight, 1718 (30%) healthy weight, 660 (12%) overweight and 3190 (56%) obese individuals. 16% (n=936) had an A1C≥6.5%. Overall, healthy weight children had 8.2 times the risk of A1C≥6.5% (95% CI 5.3 to 12.7) compared with those in the obese category. The relative risk was 13 in pre-teens (95% CI 8.5 to 20.0) and 3.9 in teenagers (95% CI 3.3 to 4.7).

CONCLUSIONS

Healthy weight was associated with a 4-13 times higher relative risk of diabetes mellitus compared with being obese. While apparently shocking, the study's fatal flaw (selection bias) explains the 'paradoxical' finding. Ignoring selection bias can delay advances in medical science.