Weight History Will Help Determine Risk of Early Death

A maximum body mass index (BMI) over a 24-year period in adulthood that falls into obesity categories I or II is associated with an increased risk of premature death compared with those whose maximum BMI remains in the normal or overweight ranges, according to new research.

"Maximum BMI in the normal-weight range was associated with the lowest risk of mortality in this cohort, highlighting the importance of obesity prevention," say Ching-Ti Liu, PhD, of the Boston University School of Public Health, Massachusetts, and colleagues, in their study published online November 16 in JAMA Network Open.

The findings therefore indicate that yo-yoing weight is not beneficial when it comes to avoiding an early death, and they seem to also suggest that losing weight slowly is preferable to dropping the pounds rapidly.

"Therefore, eliciting weight history in clinical practice may be valuable for identifying patients at increased risk of mortality," the researchers stress.

In an accompanying editorial, Mark A. Pereira, PhD, of the Division of Epidemiology and Community Health, School of Public Health, University of Minnesota, in Minneapolis, noted that the findings underscore the benefits in avoiding weight gain.

"The bottom line from these analyses was that the lowest mortality risk was observed among individuals who remained in the normal weight or overweight categories over time."

Failure to Include Weight History in Research Will Bias Results

In the extensive research looking into the link between obesity and mortality, many studies rely on weight assessed at a single point in time, which leaves open the looming possibility of reverse causality — or weight status that is influenced by a medical condition, rather than vice versa.

To take a different approach, Liu and colleagues turned to longitudinal data on 6197 people from two generations enrolled in the Framingham Heart Study.

They first calculated participants' maximum BMI over 24 years of weight history and then assessed mortality over a subsequent mean 17 years of follow-up. The beginning of the follow-up period, when patients were a mean age of 62.7 years, was considered baseline in order to determine the role of weight history over the previous 24 years in subsequent mortality.

Over the course of follow-up, 3478 (56.1%) patients died and a monotonic association was seen between maximum BMI and mortality, with the risk increasing with obese I (BMI 30 to < 35 kg/m²; hazard ratio [HR], 1.27) and obese II (BMI 35 to < 40 kg/m²; HR, 1.93) categories.

A similarly significant association between maximum weight and mortality was not observed for the overweight category (BMI of 25 to < 30 kg/m²; HR, 1.08).

Even after achieving normal weight, mortality rates were higher among individuals who were previously overweight (47.5 per 1000 person-years) and obese (66.7 per 1000 person-years) compared with those who never exceeded normal weight (27.9 per 1000 person-years).

In analyses limiting the sample to never smokers, overweight emerged as a significant risk factor for mortality, with a significant association between a maximum BMI in the overweight range and mortality (HR, 1.31).

In addition, men had greater premature mortality risks than women.

"Prior studies of mortality risks of obesity have typically used a single point in time to measure adiposity status," the authors explain. "Our study findings indicate that failure to incorporate weight history may introduce substantial bias into assessment of risk."

"Specifically, in analyses stratified by weight history, mortality risks were found to be substantially higher in normal-weight individuals who had a history of overweight or obesity compared with those who maintained a normal-weight status over time."

Slow Weight Loss Better Than Rapid

An additional sensitivity analysis showed that individuals who experienced rapid weight loss had higher mortality risks than individuals who had slower weight loss, which possibly could be indicative of the severity of an underlying disease, the authors note.

"Regardless of the underlying mechanisms of weight loss in the present study, the fact that those who lost weight exhibited higher mortality risks in the present study reinforces the need to treat them separately from those who maintained normal weight across time, accomplished only by incorporating weight history," they explain.

In his editorial, Pereira noted that the study has some key caveats, including the fact that the participants in the study included individuals in two cohorts spanning two generations — an original cohort of participants aged 28 to 62 years commencing in 1948 and an offspring cohort of participants initiated in 1971.

"There is much information missing from these analyses that would help with interpretation, including dynamics of weight change (for example, from minimum rather than maximum BMI), weight loss intentionality, and importantly, stratification on original versus offspring cohorts," Pereira writes.

"It is still quite possible that reverse causality by underlying illness may have contributed to the weight loss results," he added.

"Nonetheless, the key finding of those with stable overweight having similar risk as stable normal weight is an important observation in support of lifestyle and environment changes to prevent chronic diseases and mortality among overweight and obese individuals," he stressed.

"Indeed, multiple large-scale randomized clinical trials of diabetes prevention have clearly shown that decreases in disease incidence are possible through improved diet and physical activity among overweight and obese individuals, whether weight loss is achieved or not."

The authors have reported no relevant financial relationships.

JAMA Netw Open. Published online November 16, 2018. Abstract, Editorial

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