April 13, 2026, 11:07 am | Read time: 6 minutes
In a large Swedish long-term study with over 620,000 participants, researchers analyzed how both weight development in adulthood and the timing of obesity onset affect mortality. The results show that weight gain in young adulthood is particularly associated with a significantly increased risk for numerous diseases. Notably, the relationships differ partially between men and women.
Weight Gain in Younger Age Particularly Critical
It is now well established that severe overweight or obesity in childhood is particularly problematic.1 They often persist into adulthood and can trigger early metabolic disorders, such as insulin resistance—a precursor to type 2 diabetes. The duration of exposure seems to be crucial. The earlier in life overweight begins, the longer the body is exposed to these risks, and the higher the later mortality risk.
Similar findings are indicated by the results of a recent study focusing on already adult individuals.2 The responsible scientists explain their research approach by stating that previous studies often only highlighted snapshots of the dangers of obesity. Typically, the causes of death were examined based on a single determined body mass index (BMI).3 Thus, it remained unclear what role the timing of weight gain plays and what potential impacts arise depending on how weight develops throughout adulthood. The present study from Sweden aimed to close this gap.
Details of the Study
The analysis is based on the Swedish cohort study “Obesity and Disease Development Sweden” (ODDS), a large nationwide data collection.4 The participant pool included 258,269 men and 361,784 women who had at least three weight measurements between the ages of 17 and 60 from 1963 to 2015.
The researchers, led by study director Huyen Le, focused on three key aspects:
- typical weight developments (called weight trajectories) between ages 17 and 60,
- the age at which obesity first occurs, and
- the speed of weight gain in different life phases.
Measurements and Methods
To accurately depict individual weight developments, the researchers used so-called linear mixed models. These are statistical methods that allow for the calculation of a personal weight curve over time from multiple measurement points. Using these models, they could determine the timing of obesity and the average annual weight gain in different age phases (17 to 29, 30 to 44, and 45 to 60 years).
Participants were then tracked through national registers until their death or other events that made further observation impossible, such as emigration; without such an event, observation ended in 2020. The follow-up period averaged 23.3 years for men and 11.7 years for women. To assess mortality risk, the researchers used Cox regressions. This method determines the relative mortality risk (hazard ratio) considering various factors such as initial weight, participants’ education level, and smoking behavior.
Analysis Shows: Weight Gain Before 30 Particularly Dangerous
During the observation period, a total of 86,673 men and 29,076 women died. The average modeled weight gain was about 0.42 kilograms per year for both genders.
The study clearly shows that weight gain in young adulthood is a crucial risk factor. Those who gained more weight between the ages of 17 and 29 had a significantly increased risk of premature death. Specifically, this risk increased by 18 percent for men and 16 percent for women per additional weight gain of 0.5 kilograms per year.
The connection was particularly evident in the timing of obesity development. Individuals who became obese at a young age had a higher mortality risk than those who did not develop severe overweight by age 60. For men, the risk increase was about 69 percent, and for women, about 71 percent.
The Role of Long-Term Changes
Participants with particularly strong weight gain throughout adulthood had a significantly increased risk for numerous causes of death. These included cardiovascular diseases, various cancers, type 2 diabetes, and diseases of the digestive and urinary systems. Weight gain in later life phases generally showed weaker associations with mortality.
However, there was an important exception—among women. Here, weight gain in all age phases was similarly strongly associated with an increased risk of cancer deaths. A possible explanation is hormonal changes, as fat tissue becomes an important source of estrogens after menopause.
The study vividly demonstrates: It is not only crucial whether weight gain occurs, but also when. Early weight gain seems particularly harmful—most likely because the body is exposed to the negative effects of being overweight for many years. The earlier harmful processes begin, the longer they persist—and the higher the risk for diseases and premature death.
Overweight teenagers have an increased risk for 17 types of cancer in adulthood
Fitness or body weight – which is more important for your health?
Study Director Explains the Significance of the Results to FITBOOK
In response to FITBOOK’s inquiry, study director Huyen Le explains that early adulthood is a particularly sensitive phase for long-term health. The most important explanation she cites is the longer duration of exposure to being overweight. The decisive factor is the long period lived with obesity. “The central driver is the cumulative time with obesity or excess body fat, not weight gain at a specific age.”
However, as described, the cancer mortality of women simultaneously showed that for some individuals, weight gain later in life can have similarly strong associations as in young years. For prevention, the researchers deduce that measures should be taken as early as possible. “We are convinced that prevention strategies should focus more on young adults and maintaining a healthy body weight.” Ideally, prevention should start even earlier—preferably in childhood and adolescence. Besides individual behavior, the environment is crucial. It is particularly effective to “reduce the structural causes of a sedentary lifestyle and make healthy choices easier and more accessible for young people.”
Limitations of the Study
The study is one of the most comprehensive analyses ever conducted on the topic. The combination of a relatively high number of participants with repeated weight measurements over several decades allows for a particularly detailed examination of weight development throughout adulthood. The study is based on high-quality, nationwide registry data that enable long and nearly seamless tracking of participants.
Nevertheless, various limitations should be noted. As an observational study, only correlations can be derived, not definitive cause-and-effect relationships. Additionally, not all relevant lifestyle factors were available. Information on diet, physical activity, alcohol consumption, or existing preconditions was incomplete. Smoking was also only recorded as “yes or no,” not the extent. This limits the significance and accuracy of this crucial influencing factor.
It should also be considered that it was not distinguished whether documented weight losses were intentional or due to illness. Furthermore, the two-stage statistical method used may lead to a slight underestimation of the uncertainties of individual estimates.