The first large study looking at dairy consumption and cancer risk in Chinese adults found that higher consumption was associated with increased risks of liver cancer and breast cancer in women.
To date, the overall evidence on whether dairy consumption affects cancer risk is inconsistent. Studies in 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 for breast or prostate cancer. other types of cancer. However, these results may not be the same for non-Western populations, where the amounts and types of dairy consumption and the ability to metabolize dairy 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. Additionally, most Chinese adults cannot properly metabolize dairy products due to a lack of lactase, a key enzyme for breaking down lactose from milk sugar.
To determine whether dairy products affect cancer risk differently among Chinese people, researchers from Oxford Population Health, Peking University and the Chinese Academy of Medical Sciences in Beijing, today published the results of a new large-scale study on BMC Medicine. This collected data from more than 510,000 participants in the China Kadoorie Biobank study.
The participants (59% female, 41% male), who came from ten geographically diverse regions across China and joined the study between 2004 and 2008, had no history of cancer. During recruitment, each participant (aged 30 to 79) completed a questionnaire on the frequency of consumption of different food products, including dairy products. 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 consumed dairy products (non-consumers).
Participants were followed for about 11 years on average, and researchers used data from national cancer and death registries as well as health insurance records to identify new cancer diagnoses. Fatal and non-fatal events were included. Data analyzes took into account a range of other factors that may affect cancer risk, including age, gender, region, family history of cancer, socioeconomic status (i.e. education and income), lifestyle factors (i.e. physical activity, soy consumption and fresh fruit consumption), 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 (20%) of participants regularly consumed dairy products (mostly milk), 11% consumed dairy products monthly, and 69% were non-consumers. Average consumption was 38 g per day in the overall study population and 81 g per day among regular dairy consumers (compared to an average consumption of around 300 g per day among UK Biobank participants) .
- During the study period, 29,277 new cases of cancer were recorded, with the highest rate being lung cancer (6,282 cases), followed by female breast cancer (2,582 cases), stomach (3,577 cases), colorectal (3,350 cases) and liver (3,191 cases). case).
- People who regularly consumed dairy products had significantly higher risks of developing liver and breast cancer. For each intake of 50g/day, the risk increased by 12% and 17% respectively.
- Regular consumption of dairy products was associated with an increased risk of lymphoma (although this was not statistically significant).
- There was no association between dairy consumption and colorectal cancer, prostate cancer, or any other type of cancer studied.
Liver and breast cancers are among the most common types of cancer in China, accounting for about 393,000 and 368,000 new cancer cases respectively each year. Although these study results do not prove causation, there are several plausible biological mechanisms that may explain these associations, according to the researchers. Higher consumption of dairy products, for example, can increase levels of insulin-like growth factor (IGF-I), which promotes cell proliferation and has been linked to higher risks for several types of cancer. Potentially, the female sex hormones found in cow’s milk (such as estrogen and progesterone) may play a role in the increased risk of breast cancer, while the saturated and trans fatty acids in dairy products may increase the risk of breast cancer. 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 Kakkoura, nutritional epidemiologist at Oxford Population Health and first author of the study, said: “This was the first major study to investigate the link between dairy products and cancer risk in a Chinese population. Further studies are needed to validate these current findings, establish whether these associations are causal, and investigate potential underlying mechanisms involved.
Although the average level of consumption of dairy products in China is still much lower than that of European countries, it has increased rapidly over the past decades.
Associate Professor Huaidong Du, Principal Investigator at Oxford Population Health, and one of the study’s co-lead authors, added: “Although our results suggest there may be a direct link between regular consumption of dairy products and certain cancers, it is important to know that dairy products are a source of protein, vitamins and minerals It would not be prudent to reduce the consumption of dairy products only based on the results of the current study or without ensuring adequate intake of protein, vitamins and minerals from other sources.
The study is published in BMC Medicine.
This work was supported by Wellcome through its Livestock, Environment and People (LEAP) programme.
- World Cancer Research Fund/American Institute for Cancer Research. Meat, fish and dairy products and cancer risk. Continuous update of the 2018 project expert report.
- “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, DOI: 10.1016/S2468-1253(17)30154-1
- The full list of site-specific cancer types investigated by the study is as follows: bladder, cervical, colorectal, endometrial, female breast, kidney, laryngeal, leukaemia, liver, lung, lymphoma, oesophageal, oral cavity, ovarian, pancreatic, prostate, and stomach.
- “Current cancer situation in China: good or bad news from the 2018 Global Cancer Statistics?” by Rui-Mei Feng, Yi-Nan Zong, Su-Mei Cao and Rui-Hua Xu, 29 April 2019, Cancer communications.