Milk Causes Cancer = Preposterous?

Cancer was responsible for around three million deaths in China in 2020. Though it is difficult to determine an individual's cancer risks, it is now clear that certain elements can increase the probability of developing the disease. In China, nearly half of the deaths from cancer were caused by risk factors that are preventable. These include smoking, lack of physical activities, unhealthy diet, alcohol consumption, obesity, diabetes, infectious diseases, and environmental factors like air pollution. Smoking has long been one of the most eminent causes of cancer deaths in China, according to the Statista May 2022 report.

In a first major study to investigate cancer risk and dairy consumption in Chinese adults, researchers from Oxford Population Health, Peking University, and the Chinese Academy of Medical Sciences, Beijing have found that greater intake was associated with higher risks of liver cancer and female breast cancer.

Published on May 6, 2022 the results of a new large-scale study in BMC Medicine found that both liver and breast cancer are among the most common types of cancer in China, accounting for around 393,000 and 368,000 new cancer cases each year respectively. While these study results do not prove causation, there are several plausible biological mechanisms that may explain these associations, according to the researchers. The study has collected data from over 510,000 participants in the China Kadoorie Biobank Study.

Greater dairy consumption, for instance, may increase levels of insulin-like growth factor-i (IGF-I), which promotes cell proliferation and has been associated with higher risks for several types of cancer. Potentially, female sex hormones present in cow's milk (such as oestrogen and progesterone) may have a role in the increased risk of breast cancer, whilst saturated and trans-fatty acids from dairy products may increase the risk of liver cancer. For the majority of Chinese people who do not produce enough lactase, a key enzyme for breaking down the milk sugar lactose and dairy products may also be broken down into products that affect cancer risk.

The study noted that overall, around a fifth (20 per cent) of the participants consumed dairy products regularly (primarily milk), 11 per cent consumed dairy products monthly, and 69 per cent were non-consumers. The average consumption was 38g per day overall in the whole study population and 81g per day among regular dairy consumers (compared with an average consumption of around 300g per day in participants from the UK Biobank).

During the study period 29,277 new cancer cases were recorded, with the highest rate being for lung cancer (6,282 cases), followed by female breast (2,582 cases), stomach (3,577 cases), colorectal (3,350 cases) and liver cancer (3,191 cases). People who consumed dairy products regularly had significantly greater risks of developing liver and breast cancer. For each 50g/day intake, the risk increased by 12 per cent and 17 per cent respectively. Regular dairy consumption was associated with an increased risk of lymphoma (though this was not statistically significant).

This study has gained significance as we found out that the demand for dairy products among the Chinese population has grown at an average rate of 3.6 per cent over the past 10 years. Household dairy consumption jumped in the past two years, with per capita consumption rising 11.8 per cent year on year to 42.3 kg in 2021.

India, which has around 2.25 million people living with cancer and every year, over 11,57,294 new cancer patients registered and cancerrelated deaths totalling to 7,84,821 (2018 data). Cancers of oral cavity and lungs account for over 25 per cent of cancer deaths in males and cancer of breast and oral cavity account for 25 per cent cancers in females, according to Cancerindia.org. And India's per capita milk consumption at 406 grams (g)/day (2019-2020), already exceeds the world average of 305 g/day (2020), according to USDA'S report.

Taking cue from the Chinese study, India should also take up a similar approach in understanding whether dairy products affect the risk of cancer differently among Indians.