When people gain weight in the course of their lives can play a decisive role in their health decades later. A large-scale study by Lund University in Sweden with more than 600,000 participants investigated the extent to which weight changes between the ages of 17 and 60 are linked to the risk of dying from various diseases. The results indicate a clear trend: weight gain in the early adult years has the strongest influence on long-term health.
It has long been known that obesity increases the risk of many diseases. Rather than just focusing on obesity at one point in time, this study looked at how weight changes throughout adulthood affect health. “The most consistent finding is that weight gain at a younger age is associated with a higher risk of premature death later in life compared to people who gain less weight,” said Tanja Stocks, associate professor of epidemiology at Lund University. She is one of the researchers behind the study, which was published in eClinicalMedicine.
Faster Weight Gain Associated With Higher Mortality
The study followed over 600,000 people using data from various sources. Only people whose weight had been measured at least three times, for example at the start of pregnancy, during military service or as part of research studies, were included. During the study period, 86,673 men and 29,076 women died. The researchers tracked how body weight changed between the ages of 17 and 60 and compared these patterns with the risk of dying from all causes and obesity-related diseases. On average, both men and women gained about 0.4 kg per year.
The analysis showed that people who gained weight faster in adulthood were at higher risk of dying from obesity-related diseases. Those who developed obesity between the ages of 17 and 29 had an approximately 70 percent higher risk of premature death compared to people who did not become obese before the age of 60. The onset of obesity was defined as the time when a person’s body mass index – a weight and height-based measure (kg/m²) – first reached 30 or more. “One possible explanation for why people with early-onset obesity are at higher risk is the longer duration they are exposed to the biological effects of obesity,” said Huyen Le, PhD student at Lund University and first author of the study.
Exception for Cancer Risk in Women
There was one notable exception in the results. For cancers in women, the timing of weight gain did not appear to affect the risk level. “The risk was about the same regardless of when the weight gain occurred. If long-term exposure to obesity were the underlying risk factor, earlier weight gain should mean a higher risk. The fact that this is not the case suggests that other biological mechanisms may also play a role in cancer risk and survival in women,” Huyen Le noted.
One possible explanation could be hormonal changes associated with menopause. “If our findings in women reflect what happens during menopause, it begs the question: which came first – the chicken or the egg? It could be that hormonal changes affect weight and that age and the length of time these changes occur play a role – and that weight simply reflects what’s going on in the body.” During this phase, oestrogen levels fall and the metabolism changes at the same time. Adipose tissue then partially takes over the production of estrogens, which in turn can influence the growth of certain hormone-dependent tumors, such as breast or uterine cancer. This means that it is not only the amount of body fat that is decisive, but also when in life these hormonal changes occur and how they interact with weight.
In addition, weight gain in women can often itself be a result of hormonal processes – for example, due to changes in metabolism, appetite or fat distribution during the menopause. This makes it more difficult to clearly separate cause and effect. In this context, weight could be a “marker” for underlying biological changes rather than the sole trigger for the increased risk of cancer.
Understanding the Increase in Risk
A key strength of the study is the use of repeated weight measurements over many years. This allowed the researchers to estimate long-term weight changes with greater accuracy. Many previous studies rely on people remembering their previous weight, which can be less reliable. “The majority of weight measurements in this study were instead taken by a professional, such as a healthcare professional. The predominance of objectively measured weights in the study contributes to more reliable and robust results.
Increases in risk at the population level can be difficult to interpret. For example, a 70 percent increase in risk means that if 10 out of 1,000 people in one group die during a given period, about 17 out of 1,000 in the premature obesity group would die. “However, we should not get too hung up on exact risk figures. These are rarely completely accurate as they are influenced, for example, by the factors considered in the study and the accuracy of measurement of both the risk factors and the outcomes. However, it is important to recognize the patterns and this study sends an important message to decision and policy makers about the importance of obesity prevention,” Stocks explained.
The Role of an “Obesogenic Society”
Many experts describe today’s environment as an “obesogenic society”, where everyday conditions make it difficult to maintain healthy habits and easier to gain weight. High-calorie, highly processed foods are available everywhere and are often cheaper and more convenient than healthier alternatives. At the same time, conscious choices for healthy eating usually require more time, planning and sometimes higher costs. In addition, many people’s everyday lives have changed dramatically: Lack of exercise due to sedentary jobs, little physical activity in everyday life and increasing screen time are shaping lifestyles. Factors such as stress, irregular working hours or lack of sleep can also disruptthe circadian rhythm and thus have a negative impact on eating habits and metabolism.
Against this background, it is clear that obesity is not just an individual issue. Many experts see political and social measures as crucial to creating healthier framework conditions – for example through better food choices, physical activity-friendly cities or education. The aim is to make healthy choices in everyday life easier and more accessible.
The Study at a Glance – Key Findings
Overall, the study underscores that weight change is a long-term process whose effects often only become apparent over many years. The findings provide important insights for prevention and health policy, as they highlight how crucial it is to promote stable and healthy lifestyle habits from an early age. The long-term analysis of approximately 620,000 individuals shows how significantly weight trends over the lifespan can affect health. By collecting measurements multiple times between the ages of 17 and 60, changes could be recorded with particular reliability. It became clear that it is not individual snapshots but, above all, trends over time that are decisive.
The early onset of obesity was particularly striking: people who became obese in young adulthood had a significantly increased risk of premature death – around 70 percent higher than those who did not develop severe obesity until later in life. But even seemingly moderate, continuous weight gains were relevant. Even an average increase of around 0.4 kilograms per year at a young age was associated with a measurably increased risk of death.
The health effects were particularly evident in several key metabolic and cardiovascular diseases. The link with cardiovascular problems, which can range from increased blood pressure to serious events such as heart attacks and strokes, was particularly clear. Metabolic diseases also occurred more frequently, especially type 2 diabetes, in which long-term impaired blood sugar regulation plays a central role. In addition, there was a clear link to liver diseases, particularly fatty liver disease, which is closely linked to obesity and metabolic disorders. These changes often develop gradually and go unnoticed for a long time, but can impair organ function in the long term and increase the risk of further complications. There was also a link with weight gain in several types of cancer, but not in women.
Overall, it is clear that it is not only the body weight itself that is decisive, but above all its progression over many years. Weight gain that starts early and progresses over time appears to be particularly unfavorable, as it places a long-term burden on the body and affects several systems simultaneously. This creates risks that can reinforce each other across various organs and metabolic processes.