Dairy products may be a risk for some cancers
PEOPLE who regularly eat and drink dairy products could be at greater risk of developing some types of cancer, a new study has found.
Data collected from nearly 30,000 cancer cases among 500,000 Chinese adults found that regular dairy consumption was associated with significantly higher risks of liver and female breast cancers. For each 50g per day intake, the risk increased by 12% and 17% respectively.
However there was no association between dairy intake and colorectal cancer, prostate cancer or any other type of cancer investigated.
Researchers claim these results may not be the same for non-Western populations, where amounts and types of dairy consumption and ability to metabolise dairy products differ greatly.
Scientists believe greater dairy consumption 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.
They claim female sex hormones present in cow’s milk, such as oestrogen and progesterone, potentially have a role in the increased risk of breast cancer, while saturated and trans-fatty acids from dairy products may increase the risk of liver cancer.
Dr Maria Kakkoura, nutritional epidemiologist at Oxford Population Health and the 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 if these associations are causal and investigate the potential underlying mechanisms involved.”
Although the average level of dairy consumption in China remains 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 senior co-authors of the study, added:
“Whilst our results suggest there may be a direct link between regular dairy consumption and certain cancers, it is important to be aware 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 from the current study or without ensuring adequate intake of protein, vitamins and minerals from other sources.”
The results of the large-scale study, carried out by Oxford Population Health, Peking University and the Chinese Academy of Medical Sciences, Beijing, were published in BMC Medicine. The data was collected from more than 510,000 participants in the China Kadoorie Biobank Study.
The participants (59% female, 41% male) came from 10 geographically-diverse regions across China and joined the study between 2004 and 2008. None had a previous history of cancer. When recruited, each participant, aged 30-79, completed a questionnaire about how frequently they consumed different food products, including dairy.
The researchers categorised 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 up for an average of around 11 years, and the researchers used data from national cancer and death registries as well as health insurance records to identify new cancer diagnoses. Both fatal and nonfatal events were included.
The data analyses took into account a range of other factors that can affect cancer risk, including age, sex, region, family history of cancer, socioeconomic status (ie education and income), lifestyle factors (ie alcohol intake, smoking, physical activity, soy consumption and fresh fruit intake), body mass index, chronic hepatitis B virus infection (for liver cancer) and female reproductive factors (for breast cancer).