The first major study to investigate dairy consumption and cancer risk in Chinese adults discovered that higher dairy intake was associated with increased risks of liver cancer and breast cancer in women.
The general evidence so far about whether eating dairy products affects cancer risk has not been consistent. Studies in Western populations suggest that dairy products may be associated with a reduced risk of colorectal cancer and an increased risk of prostate cancer, but have not found any clear link to breast or other types of cancer. However, these results may not be the same for the non-Western population, where the amounts and types of dairy consumption and the ability to metabolize dairy products vary widely.
For example, in China there is very little consumption of cheese and butter, and the consumption of milk and yoghurt is much lower than that of the Western population. Additionally, most Chinese adults cannot properly metabolize dairy products due to a lack of lactase, a key enzyme for breaking down the milk sugar lactose.
To determine whether dairy products affect cancer risk differently in the Chinese, researchers from the Oxford University of Population Health, Peking University and the Chinese Academy of Medical Sciences, Beijing, have published the results of a new, large-scale study in BMC . Medicine. This collected data from more than 510,000 participants in the China Kadoorie Biobank study.
Participants (59% female, 41% male), who came from ten geographically diverse regions across China and joined the study between 2004 and 2008, had no prior history of cancer. On assignment, each participant (30 to 79 years old) completed a questionnaire on how often they consumed different food products, including dairy. The researchers categorized the participants into three groups: regular dairy consumers (at least once a week), monthly dairy consumers, and people who never or rarely ate dairy (non-consumers).
Participants were followed for an average of 11 years, and the researchers used data from national cancer and death registries as well as health insurance registries to identify new cancer diagnoses. Both fatal and non-fatal events are included. Data analyzes took into account a range of other factors that can influence cancer risk, including age, gender, region, family history of cancer, socioeconomic status (ie, education and income), and lifestyle factors (eg, alcohol and smoking intake, physical). activity, soy consumption, intake of fresh fruit), body mass index, chronic hepatitis B virus infection (for liver cancer), and female reproductive factors (for breast cancer).
The study found:
- Overall, about one-fifth of participants (20%) regularly consumed dairy (mainly milk), 11% consumed dairy per month, and 69% were non-consumers. Average consumption was 38g per day overall in the entire study group and 81g per day among regular dairy consumers (compared to average consumption of about 300g per day in UK Biobank participants).
- During the study period, 29,277 new cases of cancer were registered, with the highest incidence of lung cancer (6,282 cases), followed by female breast (2582 cases), stomach (3,577 cases), colorectal (3,350 cases), and liver cancer (3,191 cases). cases).
- People who regularly consume dairy products have a higher risk of developing liver and breast cancer. For every 50 g/day, the risks were increased by 12% and 17%, respectively.
- Regular dairy consumption was associated with an increased risk of developing lymphoma (although this was not statistically significant).
- There was no association between eating dairy products and colorectal cancer, prostate cancer, or any other type of cancer examined.
Liver cancer and breast cancer are the two most common types of cancer in China, accounting for about 393,000 and 368,000 new cancer cases each year, respectively. While the results of this study do not establish causation, there are several plausible biological mechanisms that may explain these associations, according to the researchers. For example, consuming more dairy products may increase levels of insulin-like growth factor (IGF-I), which promotes cell proliferation and has been associated with higher risks for many types of cancer. It is possible that the female sex hormones present in cow’s milk (such as estrogen and progesterone) may have a role in increasing the risk of breast cancer, while the saturated and trans fatty acids from dairy products may increase the risk of liver cancer. For the majority of Chinese who do not produce enough lactase, dairy products can also be broken down into products that affect cancer risk.
Dr Maria Kakora, a nutritional epidemiologist in Population Health at Oxford, and first author of the research study said: “This was the first major study to investigate the relationship between dairy products and cancer risk in the Chinese population. Further studies are needed to validate these current findings. , determine whether these associations are causal, and investigate the mechanisms underlying it.”
Although the average level of dairy consumption in China is still much lower than in European countries, it has risen rapidly in recent decades.
Associate Professor Huaidong Du, Senior Research Fellow at Oxford Population Health, and one of the study’s lead authors added: “While our findings suggest that there may be a direct link between regular consumption of dairy products and certain types of cancer, it is important to know that dairy is a source of for proteins, vitamins and minerals. It would not be wise to reduce consumption of dairy products based solely on the results of the current study or without ensuring adequate intake of protein, vitamins and minerals from other sources.”
The study was published in BMC . Medicine.
This work was supported by Wellcome as part of the Livestock, Environment, and People Program (LEAP).
- World Cancer Research Fund/American Institute for Cancer Research. Meat, fish, dairy products and the risk of cancer. Continuous update of the 2018 Project Expert Report.
- “Country, regional, and global estimates of lactose malabsorption in adults: a systematic review and meta-analysis” by Christian Loewold Storhaug, MS; Svein Kjetil Fosse, MS and Dr Lars T Fadnes, Ph.D., 6 Jul 2017, Available here.