- Obesity in young adulthood was associated with significantly increased likelihood of early-onset cancers in an observational study, a risk that persisted into middle age.
- Men had a higher cancer risk than women, and abdominal fat further increased cancer risk beyond BMI alone.
- Cancer rates were highest for thyroid, endometrial, and ovarian cancers.
Obesity in young adulthood was associated with significantly increased likelihood of early-onset cancers, with the risk persisting into middle age, a large population-based study from South Korea showed.
The 10-year cumulative incidence of any cancer ranged from 1.84% in normal-weight individuals to 2.62% in people with class II obesity (body mass index [BMI] ≥30, as defined by Asian-specific categories). The obesity-cancer association was stronger among men, and presence of abdominal and visceral fat added to the risk, as compared with BMI alone.
Analyses by cancer type showed the highest 10-year cancer rates for thyroid, endometrial, and ovarian cancer, followed by colorectal, kidney, liver, and pancreatic cancers. The 10-year rates of breast cancer were lower in people with obesity than normal-weight young adults, reported Kyungdo Han, PhD, of Soongsil University in Seoul, and colleagues in the Annals of Internal Medicine.
“Although the absolute risk differences were modest, the consistency of associations across multiple cancer types and the young age of the population underscore the potential importance of early-life weight management,” the authors stated. “Future research should include prospective studies to determine whether intentional weight loss in early adulthood reduces subsequent cancer risk and to identify clinical settings in which early cancer screening for young adults with obesity might be warranted.”
The findings reinforce and add to existing evidence linking cancer and obesity, said Alpa Patel, PhD, of the American Cancer Society in Atlanta. The low absolute cancer rates reflect the age group studied (19-39), which has an overall low risk of cancer.
“This study provides additional insights into early-onset cancers, which are not as well represented in older studies,” Patel, who was not involved in the study, told MedPage Today. “This is also a more contemporary study population, with the start of the follow-up period occurring between 2009 and 2012, so the trends reflect more of the current landscape. For example, the authors report that individuals in the higher BMI categories are more likely to currently smoke, whereas historically, current smoking was more common among individuals with a lower BMI.”
One notable limitation was that the authors reported smoking status but not smoking intensity or duration, which also contribute to cancer risk, she added.
More than a dozen cancers have a significant association with overweight and obesity. One recent study suggested that up to 10% of the total global cancer burden might be attributed to overweight and obesity. Within the context of a global rise in obesity prevalence, multiple studies have shown recent increases in early-onset cancers. Most studies of the obesity-cancer association have included limited information on young adults. Moreover, cancer prevention strategies have focused on middle-age and older populations, Han and colleagues noted.
The authors specifically examined associations between obesity and early-onset cancer risk in young adults, which they defined as ages 20-39. Using a national health insurance database for the years 2009-2021, investigators identified 6.3 million adults within the specified age range who underwent at least one national health examination during 2009-2012.
Investigators accounted for multiple covariates, including smoking status, alcohol intake, physical activity, residential area, income level, and comorbid conditions. BMI was divided into five groups in accordance with World Health Organization criteria for Asian populations. Participants also were categorized by waist circumference and abdominal obesity status.
The study population had a mean age of 30.9, and men accounted for 59.3% of the study population. During a mean follow-up of 11.2 years, 151,893 cancers were documented in the study population. Stratification by BMI resulted in the following 10-year cumulative cancer incidences:
- Normal weight: 1.84%
- Class I obesity: 2.24%
- Class II obesity: 2.62%
Individuals with class I obesity and abdominal obesity had a 10-year cumulative cancer incidence of 2.45% versus 2.13% for class I obesity without abdominal obesity and 2.20% for class II obesity without abdominal obesity. As compared with normal-weight individuals, the hazard for cancer over 10 years increased with rising BMI:
- Overweight: HR 1.10 (95% CI 1.08-1.11)
- Class I obesity: HR 1.22 (95% CI 1.20-1.24)
- Class II obesity: HR 1.43 (95% CI 1.39-1.47)
Cancer hazards were higher for men (1.13, 1.29, and 1.58 across the BMI categories, respectively) as compared with women (1.08, 1.15, and 1.28).
