- Design
- Nationwide population-based cohort
- Population
- 6,313,338 Korean adults aged 20–39 without prior cancer
- Primary outcome
- Incident cancer
- Effect
- 10-year incidence 2.62% (class II obesity) vs 1.84% (normal weight); difference 0.78% (0.73–0.82)
This nationwide cohort, published in Annals of Internal Medicine on 27 October, followed 6,313,338 Korean adults aged 20–39 from a health screening programme for a mean of 11.2 years. BMI was classified with Asian-specific cut-offs.
Ten-year cancer incidence was 1.84% at normal weight, 2.24% in class I obesity and 2.62% in class II obesity — absolute differences of 0.40 and 0.78 percentage points. Waist mattered too: class I obesity with abdominal obesity carried a higher incidence (2.45%) than class II obesity without it (2.20%). The highest incidences were for thyroid, endometrial and ovarian cancer. Obesity was not associated with breast cancer diagnosed by age 50.
This is observational, limited to people attending screening, and smoking was incompletely captured. The absolute differences are small for any individual. The relevance to India is the use of Asian thresholds and the weight given to waist circumference, both of which apply to South Asian patients.
- Measure waist circumference as well as BMI in young adults; abdominal obesity added risk beyond BMI here.
- Use Asian BMI thresholds when classifying obesity in South Asian patients.
- Young adults with obesity and new thyroid, menstrual or pelvic symptoms are worth a lower threshold for investigation.
- Frame weight management in young adults around long-term risk, without overstating a small individual cancer risk.
Why it matters
It adds early-onset cancer to the case for treating obesity in young adults, and shows waist adds information BMI misses.
Don't overread it
Observational data: it cannot show that weight loss in young adults would prevent these cancers.
The statistics, in plain English
The relative increase sounds large, but the absolute difference is under one percentage point over ten years: about 8 extra cancers per 1,000 people with class II obesity. The confidence intervals are very narrow because the cohort is huge, which makes the estimate precise, not necessarily unconfounded.
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