Because many Chinese have difficulty digesting and absorbing lactose, and the intake of dairy products has been low, relevant studies in the Chinese population are limited.
Recently, a paper was published inBMC MedicineThe study adds important evidence for the impact of dairy consumption on cancer in Chinese.Data from a follow-up of 500,000 people in different regions of China for more than 10 years show that,Among Chinese adults, higher intake of dairy products is associated with higher risk of liver cancer, female breast cancer, and overall cancer. The paper states that,The study is “the first and largest prospective cohort study in China” on dairy products and cancer risk.
The research was conducted by experts from the University of Oxford, School of Public Health, Peking University, Fuwai Hospital, Chinese Academy of Medical Sciences, Chinese Academy of Medical Sciences, Henan Center for Disease Control and Prevention, and China National Center for Food Safety Risk Assessment..
The research team also objectively stated in the paper,Despite adjusting for a range of confounding factors, the study wasn’t strong enough to confirm that the association was causal.These findings, and the accumulation of evidence from more future studies, may provide important information for evidence-based dietary recommendations for cancer prevention suitable for the Chinese population.
Currently,The Dietary Guidelines for Chinese Residents (2022) recommends that,Healthy people aged 2 and above should drink 300ml to 500ml of dairy products or an equivalent amount of dairy products every day.
research method
This large-scale prospective study is based on the China Kadoorie Biobank (CKB), covering approximately 510,000 people. The participants, who joined the study between 2004 and 2008, at an average age of 52 years, came from five urban areas in Qingdao, Harbin, Haikou, Suzhou, and Liuzhou, and five in Sichuan, Gansu, Henan, Zhejiang, and Hunan. rural area. None of the participants had cancer when they joined the study.
The researchers recorded the dietary habits of the participants in the past year through questionnaires. To facilitate the evaluation of diets, the researchers divided all foods into 12 groups, namely rice, wheat products, whole grain products, red meat, poultry, fish, eggs, total dairy products, fresh vegetables, preserved vegetables, fresh fruits, and beans Food intake frequency was divided into 5 categories, i.e. daily, 4-6 days per week, 1-3 days per week, monthly, and never/rarely. The vital health status of the participants was determined based on information from the China Disease Surveillance System, the Cancer Registry and the National Health Insurance Claims Database.
Research result
Across all participants, the average daily dairy intake was 37.9 grams.20.4% of the participants consumed dairy products at least once a week (with a habit of regular consumption), and their average daily intake was 80.8 grams. 68.5% never or rarely consume dairy products.Dairy intake in urban areas is higher than in rural areas for both genders.
After an average follow-up of 10.8 years, a total of 29,277 people developed cancer. Investigators were stratified by age at risk, sex, and region, and based on family history of cancer,educate, income, alcohol intake, smoking, physical activity, soy and fresh fruit intake, and body mass index (BMI) were adjusted for: dairy intake and overall cancer risk, as well as some specific The cancer risk of the site was significantly positively correlated (P<0.05).
Specifically,Daily intake of dairy products for every 50 grams:
Linked to a 7% increased risk of cancer overall（HR = 1.07，95% CI 1.04–1.10） ；
was associated with a 12% increased risk of liver cancer (n=3191) (HR=1.12, 95% CI 1.02–1.22) and was not associated with hepatitis B infection;
was associated with a 19% (HR=1.19, 95% CI 1.01–1.41) increased risk of breast cancer in women (n=2582);
was associated with a 17% (HR=1.17, 95% CI 1.07–1.29) increased risk of lymphoma (n=915).
After adjusting the data multiple times, the researchers found that,The association of dairy product intake with the risk of developing lymphoma was not statistically significant. Also, no significant association was observed between dairy intake and colorectal or other cancers.
The researchers also found that,compared with those who ate no or less dairy products,People who have the habit of consuming dairy products on a regular basis:
They were more likely to be female, had higher education, higher income levels, and were generally in better health, but were also slightly more likely to have a history of cardiovascular disease or diabetes.
Average height is taller (0.6 cm tall) and longer legs (0.3 cm long).
Both body weight and BMI were lower, with a mean BMI lower in men by 0.4 kg/kgm2, BMI was on average 0.5 kg lower in women/m2. But no clear association between dairy intake and waist circumference or body fat was observed.
Summarize
The paper concludes,Higher dairy intake may be associated with higher risk of liver cancer, female breast cancer, and lymphoma among Chinese adults with relatively low dairy intake. The effect of dairy intake on cancer was independent of other lifestyle factors, including obesity. The possible mechanisms are:
Higher intake of dairy products may lead to increased plasma insulin-like growth factor-I (IGF-I), which plays a key role in cell proliferation and cancer development.
Milk contains higher levels of branched-chain amino acids, lactose, and IGF-I, which can activate and enhance the mechanism of rapamycin complex 1 (mTORC1) signaling, thereby promoting cell proliferation, which may lead to carcinogenesis.
Saturated fatty acids (SFA) and trans fatty acids in dairy products may be associated with insulin resistance and elevated levels of proinflammatory cytokines, which may be risk factors for the development of liver cancer and lymphoma.
In recent decades,Although Chinese dairy intake has increased substantially(average intake increased from 14.9 g/day in 1992 to 24.7 g/day in 2012),but still much lower than other countries(For example, in 2015, the per capita intake in the United States was about 400 grams per day).The study’s analysis of height also supports the role of dairy in slowing bone loss.
The study also has limitations, such as the fact that only a subset of major food groups were collected in the questionnaire, and there was no total energy, specific nutrients (such as SFA and calcium) or specific dairy intake, the paper said. Also, despite the large number of cancer cases documented, the statistical power for some less common cancer sites, such as prostate cancer, remains low, and even for common cancer types, the number of cases may not be sufficient to be derived in subgroup analyses Reliable results (eg difficult to analyze breast cancer risk associated with estrogen receptor status).
In the future, more research is needed to further explore the potential mediating role of lactose intolerance between dairy intake and cancer risk. Looking forward to future research to determine its causality and underlying mechanisms.
References
[1] Kakkoura， M.G。， Du， H。， Guo， Y。 et al。，（2022）。 Dairy consumption and risks of total and site-specific cancers in Chinese adults： an 11-year prospective study of 0.5 million people.BMC Med 20， 134 （2022）。 https://doi.org/10.1186/s12916-022-02330-3
