A new study has revealed that weight gain not only affects human health as we age, but the timing of weight gain may be a crucial factor in determining the risk of premature death.
Obesity that begins in early adulthood is associated with significantly higher mortality rates compared to those who maintain a normal weight for a longer period.
The study showed that people who first became obese between the ages of 17 and 29 were nearly 70% more likely to die from any cause during the follow-up period, compared to those who did not become obese until the age of 60.
The study, conducted by a team from Lund University in Sweden, aimed to track weight across life stages rather than relying on a single measurement. Researchers used data from over 600,000 people, specifically those with at least three recorded weight measurements between the ages of 17 and 60.
Researchers defined the onset of obesity as the first time the body mass index (BMI) reaches 30 or more, which is the standard adopted at the time weight measurements are taken, although modern definitions of obesity have become more sophisticated and include additional factors such as fat distribution and differentiation between fat mass and muscle mass.
Although the study does not directly prove that premature weight gain is the sole cause of death, it confirms what is scientifically known about the link between obesity and a large number of chronic health problems.
"The most consistent finding is that being overweight at a young age is associated with a higher risk of premature death later in life, compared to people who gain less weight," said Tanya Stokes, an epidemiologist at Lund University.
Researchers believe the likely reason for this is that the body remains under biological stress for a longer period due to obesity, increasing the chances of developing chronic health problems such as inflammation, insulin resistance, heart disease, and organ damage over time.
The team tracked overall mortality rates, as well as deaths related to cardiovascular disease, various types of cancer, and type 2 diabetes, which are among the most prominent diseases associated with obesity.
The results showed that people who gained the most weight during their lifetime were the most likely to die, with cardiovascular diseases, such as heart attacks and strokes, accounting for the largest proportion of these cases.
The researchers wrote in the scientific paper: "Our results suggest that the duration of obesity, and not just weight gain in later stages of adulthood, may be the main factor behind the increased risk of death."
They added that long-term exposure to insulin resistance and chronic inflammation, in addition to coagulation disorders resulting from substances secreted by fatty tissues, may explain this increase in mortality rates.
The study also linked obesity to deaths from type 2 diabetes and some types of cancer, but some cases, such as bladder cancer in men and stomach cancer in women, did not show a clear statistical correlation.
The researchers noted differences between men and women, particularly with regard to cancer in women, as the risk of death associated with obesity was similar regardless of when the weight gain occurred, suggesting that other factors may be more influential, such as hormonal changes associated with menopause.
They pointed out some limitations in the study, including the failure to account for the impact of physical activity and diet, despite their great importance to public health, which may affect the interpretation of the results.
However, the large sample size and long follow-up period give the study significant public health importance and reinforce the call for preventing obesity at an early age rather than waiting for its effects to appear later.
To illustrate the result in numbers, if 10 out of every 1,000 people who did not develop early obesity died during the follow-up period, then about 17 out of every 1,000 people died in the group that developed early obesity.
Stokes stressed that the focus should not be solely on the precise numbers, but on the overall pattern revealed by the study, saying: "These results carry an important message for decision-makers and politicians about the need for early intervention to reduce obesity."
The study was published in the journal eClinicalMedicine.
