New research links dairy to increased risk of cancer

To date, studies have reported contrasting associations of dairy product consumption with certain cancers. These include a positive association with prostate cancer, as well as inverse associations with colorectal and premenopausal breast cancers.

In China, however, cancer rates and dairy consumption levels differ significantly from those of Western populations. Very little cheese and butter are consumed in China, for example, and consumption of milk and yogurt is much lower than that of Western populations.

Additionally, it is well documented that Chinese adults cannot properly metabolize dairy products due to a lack of lactase – a key enzyme for breaking down lactose from milk sugar.

To better understand how the links between dairy products and cancer risk may differ among Chinese people, researchers from Oxford Population Health, Peking University and the Chinese Academy of Medical Sciences in Beijing, published a new large-scale study in BMC Medicine​.

How many dairy products do adults in China consume?

The researchers relied on data collected from around 500,000 adults at the China Kadoorie Biobank, living in ten diverse regions (a mix of rural and urban areas) across China between 2004 and 2008.

Participants were surveyed and re-surveyed throughout the period, to learn about their consumption of major food groups, including dairy products.

The results revealed that, overall, 20.4% of participants reported consuming dairy products (mostly milk) on a regular basis, meaning one day a week or more. The average estimated consumption was 80.8 g per day in this population and almost 40 g per day in all participants.

Eleven percent of the participants consumed dairy products monthly and 69% never consumed any.

Incident-based follow-up research of cancer cases. Results were adjusted for family history of cancer, education, income, alcohol consumption, smoking, physical activity, soy and fresh fruit consumption, and body mass index.

Overall, 29,277 new cases of cancer were recorded, with regular dairy consumers having significantly higher risks of liver and breast cancer.

For every 50 g of dairy products consumed per day, the risk increases by 12% for liver cancer and 17% for breast cancer.

There was also an increased risk of lymphoma, although this was not considered statistically significant. No significant association was found for any other type of cancer studied.

Linking dairy product consumption to cancer risk

Although the results of these studies do not prove causation, the researchers believe that there are several plausible biological mechanisms that may explain these associations.

It could be, for example, that higher consumption of dairy products increases levels of insulin-like growth factor (IGF-I), which promotes cell proliferation and has been linked to higher risks for several types of cancer.

Another possibility is that the female sex hormones found in cow’s milk, such as estrogen and progesterone, could play a role in the increased risk of breast cancer. And the saturated and trans fatty acids in dairy products could increase the risk of liver cancer.

The researchers also noted that for the majority of Chinese people who don’t produce enough lactase, dairy products can be broken down into products that affect cancer risk.

“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.” said first author Dr Maria Kakkoura, a nutritional epidemiologist at Oxford Population Health.

Co-lead author, Associate Professor Huaidong Du, a senior researcher at Oxford Population Health, stressed that these findings should not prompt consumers to reduce their consumption of dairy products.

“While 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 dairy intake based solely on current study rights or without ensuring adequate intake of protein, vitamins and minerals from other sources.”

Source: BMC Medicine
“Dairy product consumption and risks of total and localized cancers in Chinese adults: an 11-year prospective study involving 0.5 million people”
Posted May 6, 2022
DOI: https://doi.org/10.1186/s12916-022-02330-3
Authors: Maria G. Kakkoura, Huadong Du, Yu Guo, Zhengming Chen et al.

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