- A new study suggests that people who have a weight within the healthy range in early adulthood and then gradually develop overweight — but not obesity — tend to live longer than other people.
- The adults who fell into this category tended to have a lower mortality risk than those who maintained a body mass index (BMI) in the normal range throughout their life.
- People with obesity in early adulthood who continued to gain weight as they aged were associated with the highest mortality rate.
A recent study examined how measuring an individual’s BMI over time might help estimate their risk of disease and mortality later in life.
The scientists published their findings in the Annals of Epidemiology.
“The impact of weight gain on mortality is complex. It depends on both the timing and the magnitude of weight gain and where BMI started,” says Dr. Hui Zheng, the study’s lead author and an associate professor of sociology at The Ohio State University in Columbus.
For the study, the researchers analyzed medical history data from the Framingham Heart Study (FHS), in which scientists tracked the health of three generations.
Removing the FHS participants with incomplete data left the team with 4,576 individuals from the original FHS cohort and 3,753 of the participants in the offspring cohort. The researchers further restricted their analysis to include only the individuals who were at least 31 years of age at the start of the study.
By 2011, 3,913 individuals from the original cohort and 967 individuals from the offspring cohort had died.
The researchers controlled for a variety of factors known to influence mortality, including smoking, education level, and sex.
After analyzing how the BMI of the participants evolved over the years, the researchers found that the older participants generally fell into one of seven BMI trajectories.
Among the second generation, however, there were just six BMI trajectories because few members of this group lost weight over the course of their life.
The researchers found that in both generations, those who had a healthy BMI early in adulthood and then gradually gained weight as they aged tended to live longer. However, this was only the case if they did not develop obesity.
The authors speculate that having a modest amount of extra body weight in old age may provide protection against issues such as nutritional deficiencies and loss of muscle and bone density due to chronic diseases.
Participants whose weight remained in the healthy range throughout their life had the second lowest mortality risk, followed by those who had overweight but stayed at that same weight over the course of their life. Next, came people with underweight and then, in the older generation, those who had overweight initially but lost weight as they aged.
The least likely to survive were people who had obesity in early adulthood and continued to gain weight.
“The main message is that for those who start at a normal weight in early adulthood, gaining a modest amount of weight throughout life and entering the overweight category in later adulthood can actually increase the probability of survival,” says Dr. Zheng.
The researchers found that the second generation developed overweight and obesity earlier in life than their parents.
“The higher BMI trajectories in the younger generation tend to shift upward at earlier ages relative to their parents,” Dr. Zheng says.
Due to medical advancements, the study’s authors explain, people with obesity are more likely to survive now than they were in earlier decades.
However, Dr. Zheng cautions that this trend still has ramifications for society:
“Even though the mortality risks associated with obesity trajectories have decreased across the generations, their contributions to population deaths increased from 5.4% in the original cohort to 6.4% in the offspring cohort.”
The study supports the findings of a 2013 study by Dr. Zheng and others, which found that people who had overweight in their 50s but kept their weight relatively stable over the years were more likely to survive the next 19 years.
“Now, with this study,” Dr. Zheng says, “we know more about weight trends earlier in life and how they are related to mortality.”