Young adulthood and adulthood adiposity in relation to incidence of pancreatic cancer: a prospective study of 0.5 million Chinese adults and a meta-analysis

Abstract

Background: Adult adiposity is positively associated with pancreatic cancer in Western populations. Little is known, however, about the association in China where many have lower body mass index (BMI) or about the relevance of young adulthood adiposity for pancreatic cancer in both Western and East Asian populations.

Methods: The China Kadoorie Biobank (CKB) recruited 512 891 adults aged 30-79 years during 2004-2008, recording 595 incident cases of pancreatic cancer during 8-year follow-up. Cox regression yielded adjusted HRs for pancreatic cancer associated with self-reported young adulthood (mean ~25 years) BMI and with measured adulthood (mean ~52 years) BMI and other adiposity measures (eg, waist circumference (WC)). These were further meta-analysed with published prospective studies.

Results: Overall, the mean BMI (SD) was 21.9 (2.6) at age 25 years and 23.7 (3.3) kg/m² at age 52 years. Young adulthood BMI was strongly positively associated with pancreatic cancer in CKB (adjusted HR=1.36, 95% CI 1.16 to 1.61, per 5 kg/m² higher BMI) and in meta-analysis of CKB and four other studies (1.18, 1.12 to 1.24). In CKB, there was also a positive association of pancreatic cancer with adulthood BMI (1.11, 0.97 to 1.27, per 5 kg/m²), similar in magnitude to that in meta-analyses of East Asian studies using measured BMI (n=2; 1.08, 0.99 to 1.19) and of Western studies (n=25; 1.10, 1.06 to 1.12). Likewise, meta-analysis of four studies, including CKB, showed a positive association of adulthood WC with pancreatic cancer (1.10, 1.06 to 1.14, per 10 cm).

Conclusions: In both East Asian and Western populations, adiposity was positively associated with risk of pancreatic cancer, with a somewhat stronger association for young than late-life adiposity.

Keywords: Chinese; adiposity; adulthood; meta-analysis; pancreatic cancer; young adulthood.

Figure 1

Age-specific incidence of pancreatic cancer in CKB versus Chinese national estimate in 2010. Incidence in CKB was calculated for each age at risk category and standardised by sex and region, where appropriate. Chinese national estimate was from the Global Burden of Disease Study 2010. The average incidence in CKB was 15.3 and 11.7 per 100 000 in urban and rural areas, respectively. Figure 1A shows CKB versus Chinese national estimate. Figure 1B shows urban versus rural areas in CKB. CKB, China Kadoorie Biobank.

Figure 2

Adjusted HRs for pancreatic cancer by measures of adiposity at young adulthood (aged ~25 years) and adulthood (aged ~52 years) in CKB. Young adulthood and adulthood BMI were classified as <20.0, 20.0–22.4 (reference), 22.5–24.9, 25.0–26.9 and ≥27.0 kg/m². WC was classified as <70, 70–<80, 80–<90, 90–<100 and ≥100 cm. The sizes of the boxes are proportional to the inverse of the variance of the log HRs. The models were stratified by age at risk, sex and study area, and adjusted for education, smoking and alcohol. For young adulthood BMI, smoking status at age 25 years was used in the adjustment. SD was 3.38 kg/m² for adulthood BMI, 2.59 kg/m² for young adulthood BMI and 9.74 cm for WC. Numerical values above the 95% CI represent the HR and values beneath the 95% CI represent the number of cases of pancreatic cancer in each group. The HRs and CIs are shown in online supplementary table 7. BMI, body mass index; CKB, China Kadoorie Biobank; WC, waist circumference.

Figure 3

Adjusted RRs for pancreatic cancer associated with a 5 kg/m² higher young adulthood BMI (weighted mean age of 20.9 years) in meta-analysis of CKB and four published studies. Boxes represent the RRs associated with a 5 kg/m² higher BMI at young adulthood for individual studies, with the size of the box inversely proportional to the variance of the logRR. Open boxes represent previously published studies, and the black box represents CKB. Diamonds represent summary RRs. Within categories, RRs are ordered according to their year of publication. Estimates and 95% CI of the summary RRs are in bold. Heterogeneity between studies was assessed by I² and Cochran’s Q test. BMI, body mass index; CKB, China Kadoorie Biobank; RRs, relative risks.

Figure 4

Adjusted RRs for pancreatic cancer associated with a 5 kg/m² higher adulthood BMI (weighted mean age of 51.6 years) in meta-analysis of CKB and 31 published studies, stratified by BMI assessment methods. Conventions as in figure 3. BMI, body mass index; CKB, China Kadoorie Biobank; RRs, relative risks.