Research published in the British Medical Journal finds that individuals who have never smoked tobacco and maintain BMIs between 20-24 are at the lowest risk for all cause mortality; findings suggest anything above or below said BMI range can put individuals at risk for various chronic diseases


The prevalence of obesity has increased dramatically over the past few decades. This has become a serious health concern due to the association between obesity and an increased risk of chronic diseases including cardiovascular disease, diabetes, cancer, and other morbidities. A newly-published study has conducted a meta-analysis of published cohort studies to clarify the strength of the relationship between BMI (body mass index) and all cause mortality. This study also looked at potential confounding effects of smoking, as well as if prevalent disease influenced the association between BMI and all cause mortality.

This study, published in the British Medical Journal (BMJ), collected a total of 230 cohort studies (207 publications) that looked at the association between BMI and all cause mortality. Studies were included that reported risk estimates for at least three categories of BMI in relation to all cause mortality. Data was then extracted from all the studies that were collected.

Results looked at the shape of dose-response relation curves. A J-shaped curve was seen in those who never smoked (aka “never-smokers”), and the lowest risk for all cause mortality was seen in three groups: individuals who were never-smokers with BMIs between 23-24, never-smokers who were healthy at baseline with BMIs between 22-23, and never-smokers who had a longer duration of follow-up (more than 20 years) with BMIs between 20-22. In contrast to these findings, there was a U-shaped association between BMI and mortality among current and former smokers.

This meta-analysis provides further evidence for the conclusion that obesity, as measured by BMI, increases the risk of premature mortality. The lowest mortality was observed in the BMI range of 23-24 among never-smokers, 22-23 among healthy never-smokers, and 20-22 among never-smokers with longer follow-up durations. An interesting finding to note was that the risk of mortality increased for individuals with BMIs that were too low (underweight individuals).

This research is beneficial to inform people regarding the adverse risks that accompany excess or deficient weight. This study, as well as previous research, recommends a BMI of 18.5-24.9 for the prevention of chronic diseases. Future research can focus on BMI and specific causes of death, including less common diseases contributing to mortality.




Written By: Rachel Berkovich, BSc

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