From John Ray's shorter notes
December 10, 2018
Does being fat give you heart disease?
The study below reports only two very weak associations. The association between diabetes and obesity is no surprise. It is known that diabetics tend to overeat and put on weight. But that does NOT prove that being overweight gives you diabetes.
The correlation between coronary artery disease and obesity is potentially meaningful but the association is marginal and tends to be undermined by the finding that obesity is unrelated to stroke incidence. Obesity is in other words associated with a stroke precursor but not with stroke itself. The only reasonable response to that pattern of effects is that obesity is harmless
The authors below, however, draw the conclusions that they wanted to draw -- as is very common in research reports
Association Between Obesity and Cardiovascular Outcomes
A Systematic Review and Meta-analysis of Mendelian Randomization Studies
Haris Riaz et al.
Importance: Although dyslipidemia has been consistently shown to be associated with atherogenesis, an association between obesity and cardiovascular disease outcomes remains controversial. Mendelian randomization can minimize confounding if variables are randomly and equally distributed in the population of interest.
Objective: To assess evidence from mendelian randomization studies to provide a less biased estimate of any association between obesity and cardiovascular outcomes.
Data Sources: Systematic searches of MEDLINE and Scopus from database inception until January 2018, supplemented with manual searches of the included reference lists.
Study Selection: Studies that used mendelian randomization methods to assess the association between any measure of obesity and the incidence of cardiovascular events and those that reported odds ratios (ORs) with 95% CIs estimated using an instrumental variable method were included. The 5 studies included in the final analysis were based on a consensus among 3 authors.
Data Extraction and Synthesis: Two investigators independently extracted study characteristics using a standard form and pooled data using a random-effects model. The Meta-analysis of Observational Studies in Epidemiology (MOOSE) reporting guideline was followed.
Main Outcomes and Measures: Obesity associated with type 2 diabetes, coronary artery disease, or stroke. The hypothesis was formulated prior to data collection.
Results: Of 4660 potentially relevant articles, 2511 titles were screened. Seven studies were included in the systematic review, and 5 studies with 881 692 participants were eligible to be included in the meta-analysis. Pooled estimates revealed that obesity was significantly associated with an increased risk of type 2 diabetes (OR, 1.67; 95% CI, 1.30-2.14; P < .001; I2 = 93%) and coronary artery disease (OR, 1.20; 95% CI, 1.02-1.41; P = .03; I2 = 87%). No association between obesity and stroke was found (OR, 1.02; 95% CI, 0.95-1.09; P = .65; I2 = 0%).
Conclusions and Relevance: The present meta-analysis suggests that obesity is associated with type 2 diabetes and coronary artery disease. Although this analysis of mendelian randomization studies does not prove causality, it is supportive of a causal association. Hence, health care practitioners should continue to emphasize weight reduction to combat coronary artery disease.
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