Early Weight Gain Can Have Lifelong Consequences

It has long been known that obesity increases the risk of several diseases. In this new study, researchers have instead investigated how changes in weight over the course of adulthood affect health.

"The most consistent finding is that weight gain at a younger age is linked to a higher risk of premature death later in life, compared with people who gain less weight," says Tanja Stocks, Associate Professor of Epidemiology at Lund University. She is one of the researchers behind the study, which has now been published in eClinicalMedicine.

The study is based on data from over 600,000 people, who were tracked via various registers. To be included in the study, participants needed to have had their weight assessed on at least three occasions, for example during early pregnancy, at military conscription, or as a participant of a research study. During the period studied by the researchers, 86,673 of the men and 29,076 of the women died.

The researchers analysed how weight changed between the ages of 17 and 60 and how this was linked to the risk of death overall and from various obesity-related diseases (see fact box). On average, both men and women gained 0.4 kg per year.

The results show that people who gained weight more rapidly over this adult life course had a higher risk of dying from various obesity-related diseases examined by the researchers. People with obesity onset between the ages of 17 and 29 had an approximately 70 per cent higher risk of premature death compared with those who did not develop obesity before age 60. Obesity onset was defined as the first time a person's body mass index, a measure based on weight and height (kg/m²), reached 30 or higher.

"One possible explanation for why people with early obesity onset are at greater risk is their longer period exposed to the biological effects of excess weight," says Huyen Le, doctoral student at Lund University and first author of the study.

However, the pattern differed in one instance: when it came to cancer in women.

"The risk was roughly the same regardless of when the weight gain occurred. If long-term exposure to obesity were the underlying risk factor, earlier weight gain should imply 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," says Huyen Le.

One possible explanation could be hormonal changes associated with menopause.

"If our findings among women reflect what happens during menopause, the question is which came first: the chicken or the egg? It may be that hormonal changes affect weight and the age and duration over which these changes occur - and that weight simply reflects what's happening in the body."

One strength of the study is that it is based on multiple weight measurements per individual, which enabled the researchers to estimate weight changes over decades of adulthood. Most other studies lack such data, and they also largely rely on self-reported recalled weights at a younger age.

"The majority of weight measurements in this study were, instead, taken by staff, for example in healthcare settings. The predominance of objectively measured weights in our study contributes to more reliable and robust results," says Tanja Stocks.

Increases in risk within a population can sometimes be difficult to interpret. For example, a 70 per cent increase in risk means that if 10 out of 1,000 people in the reference group die over a given period, approximately 17 out of 1,000 would die in the group with early obesity.

"But we shouldn't get too hung up on exact risk figures. They are rarely entirely accurate, as they are influenced, for example, by the factors taken into account in the study and the accuracy with which both risk factors and outcomes have been measured. However, it's important to recognise the patterns, and this study sends an important message to decision-makers and politicians regarding the importance of preventing obesity," says Tanja Stocks.

Many researchers today refer to an "obesogenic society", in which the environment hinders healthy lifestyles and promotes the development of obesity.

"It's up to policymakers to implement measures that we know are effective in combating obesity. This study provides further evidence that such measures are likely to have a positive impact on people's health."