Dairy consumption and risks of total and site-specific cancers in Chinese adults: an 11-year prospective study of 0.5 million people

Abstract

Background: Previous studies of primarily Western populations have reported contrasting associations of dairy consumption with certain cancers, including a positive association with prostate cancer and inverse associations with colorectal and premenopausal breast cancers. However, there are limited data from China where cancer rates and levels of dairy consumption differ importantly from those in Western populations.

Methods: The prospective China Kadoorie Biobank study recruited ~0.5 million adults from ten diverse (five urban, five rural) areas across China during 2004-2008. Consumption frequency of major food groups, including dairy products, was collected at baseline and subsequent resurveys, using a validated interviewer-administered laptop-based food frequency questionnaire. To quantify the linear association of dairy intake and cancer risk and to account for regression dilution bias, the mean usual consumption amount for each baseline group was estimated via combining the consumption level at both baseline and the second resurvey. During a mean follow-up of 10.8 (SD 2.0) years, 29,277 incident cancer cases were recorded among the 510,146 participants who were free of cancer at baseline. Cox regression analyses for incident cancers associated with usual dairy intake were stratified by age-at-risk, sex and region and adjusted for cancer family history, education, income, alcohol intake, smoking, physical activity, soy and fresh fruit intake, and body mass index.

Results: Overall, 20.4% of participants reported consuming dairy products (mainly milk) regularly (i.e. ≥1 day/week), with the estimated mean consumption of 80.8 g/day among regular consumers and of 37.9 g/day among all participants. There were significant positive associations of dairy consumption with risks of total and certain site-specific cancers, with adjusted HRs per 50 g/day usual consumption being 1.07 (95% CI 1.04-1.10), 1.12 (1.02-1.22), 1.19 (1.01-1.41) and 1.17 (1.07-1.29) for total cancer, liver cancer (n = 3191), female breast cancer (n = 2582) and lymphoma (n=915), respectively. However, the association with lymphoma was not statistically significant after correcting for multiple testing. No significant associations were observed for colorectal cancer (n = 3350, 1.08 [1.00-1.17]) or other site-specific cancers.

Conclusion: Among Chinese adults who had relatively lower dairy consumption than Western populations, higher dairy intake was associated with higher risks of liver cancer, female breast cancer and, possibly, lymphoma.

Keywords: Cancer; China; Dairy products; Diet; Prospective cohort study.

Fig. 1

Percentage of men and women who reported regular dairy intake by age and study area at baseline (2004–2008)

Fig. 2

Adjusted mean leg length, standing height, body weight and body mass index by frequency of dairy intake in men (M) and women (F) at baseline (2004–2008). Linear regression analyses were adjusted for age (continuous variable), region (ten regions), education (four categories), annual household income (four categories), smoking (four categories), alcohol consumption (four categories), total physical activity (continuous variable) and fresh fruit consumption (five categories). Vertical lines represent 95% CIs. Solid squares represent men and open squares represent women

Fig. 3

Associations of usual dairy intake (g/day) with the incidence of total cancer, liver cancer, lymphoma and female breast cancer. Cox regression analyses were performed among 510,146 participants with no prior self-reported history of cancer at baseline. Analyses were stratified by age-at-risk (continuous), sex (dichotomous variable) and region (ten regions) and were adjusted for education (four categories), income (four categories), smoking (four categories), alcohol consumption (four categories), total physical activity (continuous variable), family history of cancer (dichotomous), fresh fruit consumption (five categories), soy consumption (three categories) and BMI (continuous variable). B Analysis for liver cancer was additionally adjusted for HBsAg status (three categories). The y axis was plotted on a log_e scale with the lowest intake group (never/rarely) as a reference category. The estimated crude mean values of usual dairy intake (g/day) were 24.0, 44.4 and 80.8 g/day in the lowest (never/rarely), medium (monthly) and highest (regular) intake groups, respectively. The FDR-corrected P trend values for the associations with incidence of total cancer, liver cancer, lymphoma and female breast cancer were 0.002, 0.04, 0.17 and 0.01, respectively. The black squares represent HRs with the size being inversely proportional to the variance of the log_e of HR and the vertical lines represent 95% CIs. The numbers above the vertical lines are point estimates for HRs and the numbers below the lines refer to the number of incident cancer cases. Dashed diagonal lines indicate the linear associations between dairy intake and cancer risk