Do dairy products increase your risk of cancer? The verdict is out

Could dairy products such as milk, cheese and yoghurt increase your risk of cancer? We put this alarming assertion under the microscope.

Researched by Lee Mwiti

A consumer shops for dairy products in a supermarket in Kenya’s capital Nairobi in July 2014. Photo: AFP/Simon Maina

Dairy products such as milk, yoghurt and cheese “are bad for you”, stated a March article in the wellness section of a South African trade union’s website.

The Solidarity piece listed 5 “shocking” reasons why, including that it weakens your bones and induces moodiness.

A reader suggested Africa Check look into these claims. To decide on one, we put them to the vote — and our readers picked the claim that dairy products “could increase your risk of cancer”.

3 sources cited specifically referred to cancer

While saying that the link between dairy and cancer is “not conclusive”, the Solidarity article claimed that a Harvard study of 100,000 women between 26 and 46 showed those “with the highest intake of meat and dairy products ran the highest risk of breast cancer”.

Three further sources Solidarity cited specifically referred to cancer.

One, an article on women-focused US publication Bustle.com, referred to the same Harvard study. It also mentioned a more recent study published in the British Journal of Cancer, in which 22,788 lactose-intolerant participants from Sweden were followed. The results reportedly showed that “low consumption of milk and other dairy products is linked with decreased risks of lung, breast and ovarian cancers”.

A second reference was to a 2004 study, titled “Does diet affect breast cancer risk?”. Published in the Breast Cancer Research journal, it reviewed several studies to check for a relationship between dietary risk factors and breast cancer.

Lastly, Solidarity referenced a blog entry by high-profile American family physician Mark Hyman, which stated that higher intakes of calcium and dairy products may raise the risk of prostate cancer by “30–50%”.

High-fat dairy foods linked to higher breast cancer risk

The “Harvard study” Solidarity most prominently mentioned was published in July 2003. It looked at the relation between dietary fat intake and breast cancer risk among 90,655 women who haven’t yet reached menopause.

The study concluded that the “intake of animal fat, mainly from red meat and high-fat dairy foods, during premenopausal years is associated with an increased risk of breast cancer”.

One of the study’s researchers while at Harvard University, Professor Eunyoung Cho, is now at Brown University. She told Africa Check that sweeping statements should not be made about this study.

“My paper only found an association with high-fat dairy foods,” Eunyoung, who focuses on the role of diet and nutrition in the development of chronic diseases, said. “I wouldn’t generalise the finding to all of dairy products or milk.”

The researchers have submitted a manuscript with more up to date data on the topic, she added, but it is yet to be published.

The study of 22,788 lactose intolerant Swedes did find that people who used little dairy in their diet had a decreased risk of lung, breast and ovarian cancer.

But this does not mean that the converse — higher intake of dairy products means a higher risk of these cancers — is true. This Dr Jianguang Ji, who focuses on medical epidemiology at the Center for Primary Health Care Research at Sweden’s Lund University, told Africa Check.

“We cannot draw such conclusion based only on this study,” said Jianguang, one of the study’s researchers, adding that more research into any links is required.

Milk is ‘very complicated’

Radiation therapists prepare a patient for a radiation session at the Cancer Care Kenya centre in Nairobi on in December 2016. Photo: AFP/SIMON MAINA

The claim that milk increases the risk of breast cancer is unproven, a co-author of the 2003 Harvard study as well as the Breast Cancer Research journal study, Walter Willett, told Africa Check. Willett is a professor of epidemiology and nutrition at Harvard University.

“Milk is very complicated with benefits and risk. The evidence on breast cancer is still mixed,” he said. Willett mentioned studies that showed an increase in the risk of prostate cancer and to a lesser extent, uterine cancer.

However, the International Agency for Research on Cancer told Africa Check that the evidence from some prostate cancer studies is quite weak and more research is required to arrive at a more definitive conclusion. As for other cancers, dairy products and high calcium diets are related to a lower risk of colorectal cancer.

Based on published scientific evidence, there is no proven link between dairy products and breast cancer, Dr Marc Gunter, who heads the nutrition and metabolism section at the agency, told Africa Check.

“If anything there is some data from epidemiological studies suggesting that the consumption of dairy products and diets rich in calcium might be protective against breast cancer,” he said. Again, further research is needed.

Conclusion: More research on dairy’s link to cancer needed

South African trade union Solidarity published what it said were shocking reasons why people should skip the dairy product aisle at the supermarket.

One reason given was that these products could increase the risk of cancer, specifically breast cancer. But researchers of the studies quoted or linked to said their findings did not support this conclusion.

Though other studies have pointed to an increased risk of prostate cancer, more research is required to definitely say so. On the other hand, taking in dairy products and lots of calcium are related to a lower risk of colorectal cancer.

Given the lack of conclusive proof, we rate this claim unproven.

Additional reading

Fake-news alert: Male circumcision NOT linked to cancer of the penis
Claim that contraception causes cancer is misleading and alarmist
Can dates really cure cancer? The claim is nothing but dangerous quackery

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Originally published at africacheck.org.

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