The validity of body mass index (BMI) as the only predictor of all-cause mortality is further questioned by a recent study.
The majority of earlier research, according to the study’s authors, rely on more dated data that isn’t sufficiently diverse, so they’re hoping the current study may remedy that.
A BMI that indicates overweight or obesity can increase the chance of developing several chronic, fatal diseases, but it may not be a reliable predictor of mortality as a whole.
According to a recent study, it is advisable to take into account a person’s body mass index, or BMI, together with other risk variables when forecasting all-cause death. As an independent variable, BMI might not be a reliable predictor of premature death.
There was no variation in the risk of death from all causes among persons in the healthy and overweight BMI categories, from a BMI of 22.5 to 27.4, according to the research.
However, the study found that in persons with a BMI greater than 30, the risk of all-cause death rose by 21% to 108%.
No appreciable increase in mortality was observed in older persons between BMIs of 22.5 to 34.9, the higher range indicating obesity.
Older statistics on BMI and early death are displaced by new data.
Data from the 1970s that concentrated on non-Hispanic white adults formed the basis of the majority of research on BMI and mortality.
The new study examined more recent, comprehensive data while keeping in mind the changes in lifestyles since that time, including the rise in overweight and obesity, and sought a more varied study population sample.
Self-reported BMI data from 554,332 American individuals who took part in the National Health Interview Survey from 1999 to 2018 and data from the 2019 US National Death Index were used in the analysis.
The average age was 46, there were equal numbers of males and women, and 69% of the population identified as non-Hispanic white, while 12% identified as non-Hispanic Black.
Among the individuals, 35 percent had a BMI between 25 and 30, which is normally regarded as overweight, and 27.2 percent had a BMI of 30 or more, which is categorised as obesity.
A total of 75,807 fatalities were reported throughout the average follow-up period of 9 years and the maximum follow-up period of 20 years.
Why BMI is a poor indicator of health?
We spoke with Dr. Pedro J. Caraballo, medical director of the Mayo Clinic Clinical Decision Support Programme, who was not engaged in this investigation.
“It is extremely debatable whether or not BMI alone should be used to define obesity or health. Different types of obesity that may have an impact on health have clearer definitions. BMI may be easily calculated and found in any medical records, though.
A person’s BMI is calculated by dividing their weight in kilogrammes by the square of their height in metres.
However, BMI ignores other aspects of the body, such as the ratio of fat to muscle, how fat is distributed throughout the body, and metabolic health. For instance, having excess fat around the waist raises your risk of getting sick.
“[BMI] does not distinguish between muscle mass and fat mass, and some individuals, like bodybuilders, may have a high BMI because of more muscle mass,” said Dr. Dagfinn Aune, a research associate in the Faculty of Medicine, the School of Public Health at Imperial College London in the United Kingdom, who was not involved in this study.
Despite these drawbacks, according to Dr. Aune, BMI performs a good job of capturing the elevated risk of chronic disease and mortality that is connected to obesity at the population level.
BMI as a measure of obesity is “not a suitable tool”
Dr. Aune provided a lengthy list of chronic diseases linked to an oversized BMI. These included kidney stones, gallstones, diverticular disease, coronary heart disease, stroke, heart failure, sudden cardiac death, atrial fibrillation, hypertension, type 2 diabetes, and a dozen distinct cancers.
Additionally, preeclampsia, gestational diabetes, gestational hypertension, stillbirth, and infant death are just a few of the pregnancy issues that are linked to being overweight or obese while pregnant, according to Dr. Aune.
The results of this study are outdated in Dr. Caraballo’s eyes. He referenced his own research, which “showed that BMI is an independent risk factor only in extreme values, very low (20) or very high (>40), with risk stratification based on comorbidities.”
Multiple studies, according to Dr. Caraballo, have found that mild to moderate obesity “may help survival when considering a specific subpopulation that is under stress.”
He noted various papers on this subject for “heart disease, kidney disease, cancer, stroke, and rheumatoid arthritis, etc.” and concluded that maintaining energy reserves may be beneficial for people.
According to Dr. Visaria, “the United States has undergone a significant transformation since the 20th century in terms of racial/ethnic makeup, age distribution, healthcare access and treatments, and sociocultural behaviours.”
It is crucial to comprehend the relationship in a more modern population since all of these can affect the association between BMI and all-cause mortality, he said.
Dr. Visaria further emphasized the importance of utilizing the most rigorous techniques to eliminate bias and ensure that observational data is as nationally representative as feasible.
Lower risk of older adults having greater BMI
Dr. Visaria proposed theories as to why this would be the case, given that older adults did not exhibit an increased mortality risk up to a BMI of 35.
We believe that the decline in bone mineral density and sarcopenia that occurs as people age have a role in this. Despite having large quantities of fat, losing these two types of weight can cause you to have excessively normal BMIs, he warned us.
Because of their maintained bone and muscle mass, those with higher BMIs may actually be in better health.
What factors predict total mortality more accurately?
According to Dr. Caraballo, the link between fat and mortality is extremely convoluted.
“Obesity by itself, in the range of mild to moderate, may not be an independent risk factor,” he said. “However, obesity is a significant risk factor for the emergence of numerous metabolic disorders that, over time, raise the mortality risk (diabetes, heart disease, etc.). People may also put on weight when they have a chronic illness because they do less exercise and eat poorly.
In his recommendation, Dr. Visaria said that “physicians should consider supplementing BMI with other measures such as waist circumference, waist-to-height ratio, and waist-to-hip ratio.”
According to Dr. Visaria’s study, “We show that waist circumference significantly modifies the association between BMI and all-cause mortality.”
Dr. Visaria stated, “Bioimpedance scales are another alternative to determine total body fat percent, but they still need to be verified and are known to have some mistakes. Additionally, doctors should consider patients’ cardio-metabolic health factors like blood pressure, blood sugar, and cholesterol levels when interpreting adiposity measurements.
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