A large Swedish study conducted on over 600,000 people at Lund University has established a finding: gaining weight early in adulthood appears even more harmful to longevity than later weight gain, even significant weight gain. The researchers tracked weight changes between ages 17 and 60 and linked them to causes of death, offering a new way to think about prevention of obesity-related diseases.
Thus, participants were selected if they had at least three recorded weight measurements, for example during pregnancy, military service, or as part of medical studies. During the follow-up period, 86,673 men and 29,076 women died. On average, weight increased by about 0.88 pounds (0.4 kg) per year in both sexes. The study then analyzed the link between these weight trajectories and overall mortality, as well as deaths from obesity-related diseases, including cancer.
The results show that people who gained weight quickly during their adult life have a higher risk of premature death than those whose weight remained relatively stable, which is not surprising in itself.
What is striking is that those who developed obesity (body mass index of 30 or higher) between ages 17 and 29 had a risk of early mortality about 70% higher than those who did not reach that stage before age 60. A longer exposure to the biological effects of overweight could explain this difference, according to the authors.
However, a notable exception appeared in the data: the risk of cancer in women did not differ according to the age of weight gain. If prolonged exposure to obesity were the only factor, an early onset should have increased the risk. The researchers suggest that other biological mechanisms, possibly related to hormonal changes of menopause, could come into play. It is possible that hormones influence both weight and cancer risk, thus complicating the direct link.
A strength of this study is the use of repeated and objective weight measurements, often taken by medical personnel, unlike many previous studies that rely on participants' memory. This makes the results more reliable.
The researchers emphasize the importance of understanding trends rather than exact risk numbers, as these depend on many factors. For example, a 70% increase in risk means that if 10 people out of 1,000 die in a reference group, about 17 out of 1,000 die in the early-risk group.
The study was published in the journal eClinicalMedicine and received funding from several Swedish organizations.