The first major study to investigate dairy consumption and cancer risk in Chinese adults found that higher intake was associated with an increased risk of liver cancer and female breast cancer.
The general evidence so far on whether eating dairy products affects the risk of cancer has not been consistent. Studies of Western populations indicate that dairy products may be associated with a lower risk of colorectal cancer and a higher risk of prostate cancer, but have found no clear link to breast cancer or other cancers. These results, however, may not be the same for non-Western populations, where the amounts and types of dairy consumption and the ability to metabolize dairy products are very different.
For example, in China there is very little consumption of cheese and butter, and the consumption of milk and yogurt is also much lower than in Western populations. In addition, most Chinese adults are unable to properly metabolize dairy products due to lack of lactase, a key enzyme in breaking down lactose from milk sugar.
To determine whether dairy products affect cancer risk differently in the Chinese, researchers from Oxford Population Health, Peking University and the Chinese Academy of Medical Sciences, Beijing, published the results of a study today. new large-scale study in BMC Medicine. This gathered data from more than 510,000 participants in the Kadoorie Biobank Study in China.
Participants (59% women, 41% men), who came from ten geographically diverse regions of China and joined the study between 2004 and 2008, had no history of cancer. When recruited, each participant (aged 30 to 79) completed a questionnaire about how often they consumed different foods, including dairy products. The researchers classified participants into three groups: regular dairy consumers (at least once a week), monthly dairy consumers, and people who never or rarely consumed dairy products (non-consumers).
Participants were followed for an average of about 11 years, and the researchers used data from national cancer and death records, as well as health insurance records to identify new cancer diagnoses. Deadly and non-fatal events were included. Data analysis took into account a number of other factors that may affect the risk of cancer, such as age, sex, region, family history of cancer, and socioeconomic status. education and income), lifestyle factors (ie alcohol intake, smoking, activity, soy consumption and fresh fruit intake), body mass index, chronic virus infection of hepatitis B (for liver cancer) and female reproductive factors (for breast cancer).
The study found:
- Overall, about one-fifth (20%) of participants consumed dairy products regularly (mostly milk), 11% consumed dairy products monthly, and 69% were non-consumers. The average daily consumption was 38 g per day in the entire study population and 81 g per day among regular dairy consumers (compared to an average consumption of about 300 g per day in Biobank participants of the United Kingdom).
- During the study period, 29,277 new cases of cancer were registered, with the highest rate of lung cancer (6,282 cases), followed by breast cancer (2,582 cases), stomach cancer (3,577 cases), colorectal cancer (3,350 cases). and liver cancer (3,191). cases).
- People who consumed dairy products regularly had a significantly higher risk of developing liver and breast cancer. For each 50 g / day intake, the risk increased by 12% and 17%, respectively.
- Regular dairy consumption was associated with an increased risk of lymphoma (although this was not statistically significant).
- There was no association between dairy intake and colorectal cancer, prostate cancer, or any other type of cancer investigated.
Both liver and breast cancer are among the most common cancers in China, accounting for about 393,000 and 368,000 new cases of cancer each year, respectively. Although the results of these studies do not prove causality, there are several plausible biological mechanisms that may explain these associations, according to the researchers. Increased dairy consumption, for example, may increase levels of insulin-like growth factor-I (IGF-I), which promotes cell proliferation and has been associated with an increased risk of various cancers. . Potentially, female sex hormones in cow’s milk (such as estrogen and progesterone) may play a role in increasing the risk of breast cancer, while saturated and trans fatty acids in dairy products may increase the risk. of liver cancer. For most Chinese who do not produce enough lactase, dairy products can also be broken down into products that affect the risk of cancer.
Dr Maria Kakkoura, a nutritional epidemiologist at Oxford Population Health and the lead author of the research study, said: “This was the first major study to investigate the link between dairy products and cancer risk. “More studies are needed to validate these current findings, establish whether these associations are causal, and investigate the possible underlying mechanisms involved.”
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, a senior researcher at Oxford Population Health and one of the study’s senior co-authors, added: “Although our results suggest that there may be a direct link between regular dairy use and certain cancers. , it is important to note that dairy products are a source of protein, vitamins and minerals.It would not be prudent to reduce dairy consumption based solely on the results of the current study or without ensuring an adequate intake of protein, vitamins and minerals from other sources “.
The study is published in BMC Medicine.
DOI: 10.1186 / s12916-022-02330-3
This work was supported by Wellcome as part of its Livestock, Environment and People (LEAP) program.
- World Cancer Research Fund / American Cancer Research Institute. Meat, fish and dairy and the risk of cancer. Expert report of the 2018 continuous update project.
- “National, Regional, and Global Estimates of Lactose Malabsorption in Adults: A Systematic Review and Meta-Analysis” by Christian Løvold Storhaug, MS; Svein Kjetil Fosse, MS and Dr. Lars T Fadnes, PhD, July 6, 2017,