The young adulthood to midlife transition period is an important new target for obesity prevention, says An Pan

The harmful effect of obesity on health is well known. However, weight loss interventions generally have a small effect and can be difficult to sustain. The prevalence of obesity continues to increase in many countries. [1] Previous research mostly focused on promoting weight loss among people with overweight/obesity and on obesity prevention in children/adolescents or in older people. However, young adulthood is a critical period when weight gain (mostly with body fat increase) is common. The prevalence of obesity in US adults aged 20-39 years old during the period 2013-2016 was 33.2% in men and 36.8% in women, which was nearly two-fold compared with the 17.8% prevalence in US children and adolescents at the same time. [2, 3] Therefore, monitoring weight change since young adulthood and preventing excess weight gain could have an important impact on population health.

Within this context, we started to explore the relations of long-term weight change throughout adult life with mortality, especially weight change from young adulthood to midlife.

We used data from 36051 participants aged 40 years and above in the US National Health and Nutrition Examination Survey who had their measured weight and height at baseline and recalled weight at age 25 years and ten years before baseline. Since the mean age of participants was 57 (range 30-80, IQR 36-56) at baseline and 47 (range 40-90, IQR 46-66) at ten years before baseline, we approximated the period of age 25 years to ten years before baseline as the period of young adulthood to middle adulthood. Similarly, the period of age 25 years to baseline was approximated as young to late adulthood, and the ten years period before baseline was approximated as middle to late adulthood. We also did several sensitivity analyses to better reflect the age periods and check that the results were robust.

We found that overweight and obesity at early adulthood were linearly and positively associated with higher risk of mortality in later life, while the association between BMI and mortality started to attenuate and changed to U shape at middle adulthood and late adulthood. The results are consistent with many previous studies and suggest that BMI at early adulthood may be a better indicator of premature mortality in later life.

When looking at the association between weight change pattern and mortality risk, we found that stable obesity was related to higher risk compared to stable normal weight, and the association was stronger for the period from young to middle adulthood (72% higher risk) compared to the period from middle to late adulthood (20% higher risk). We further found that weight gain from young to middle adulthood was associated with increased risk of mortality from all cause and heart diseases, while the association was attenuated with increasing age. For example, compared with participants in stable normal weight group, those moving from nonobese BMI to obesity during young to middle adulthood had a 22% higher risk of all-cause mortality, while the association was attenuated to null for weigh gain pattern from middle to late adulthood. On the other hand, the association with weight loss from middle to late adulthood became stronger and significant. For example, moving from obesity to nonobese BMI from middle to late adulthood was associated with 30% higher risk of premature deaths. 

Our study provides evidence that maintaining a normal weight across adulthood, especially preventing weight gain in early adulthood, is important for preventing premature deaths in later life. More studies with multiple repeated measures are still needed to better understand the weight change pattern across life periods and its health impact. In addition, weight cycling and the underlying reasons for weight change are also important factors to be explored in future research. 

An Pan is an epidemiologist with research interests in understanding the causes and consequences of non-communicable diseases, particularly obesity and related metabolic diseases. He is a professor at the School of Public Health, Tongji Medical College, Huazhong University of Science and Technology.

Competing interests: Please see declaration on research paper. 

References:

1. Roberto CA, Swinburn B, Hawkes C, Huang TT, Costa SA, Ashe M, et al. Patchy progress on obesity prevention: emerging examples, entrenched barriers, and new thinking. Lancet. 2015;385(9985):2400-9.
2. Hales CM, Fryar CD, Carroll MD, Freedman DS, Aoki Y, Ogden CL. Differences in obesity prevalence by demographic characteristics and urbanization level among adults in the United States, 2013-2016. JAMA. 2018;319(23):2419-29.
3. Ogden CL, Fryar CD, Hales CM, Carroll MD, Aoki Y, Freedman DS. Differences in obesity prevalence by demographics and urbanization in US children and adolescents, 2013-2016. Jama. 2018;319(23):2410-8.