Highlights
Different observational studies suggest that consuming milk and dairy products may reduce the risk of colorectal or bowel cancer. However, based on limited evidence, it is found that a very high intake of milk and dairy products may increase the risk of prostate cancer in men. A similar association was also observed in Non-Hodgkin’s Lymphoma. There is no consistent evidence to confirm the association between milk and dairy product consumption and the risk of breast cancer. More well-defined clinical studies are required to test these associations.
Milk and Dairy Products
Milk and dairy products are consumed by millions of people worldwide and are included as part of their daily diet. Milk is either consumed raw or pasteurized and is also processed into various milk products such as cheese, cream, concentrated milk, butter and ghee. Milk and dairy products are excellent sources of calcium, which is good for bones and helps reduce the fractures, and nutrients such as proteins, fats, minerals and vitamins. Some of the active components present in milk and dairy products include Allantoin, Citric acid, Calcium, Casein, gamma-Linolenic acid, Lactoferrin, Lactose, Lauric acid, Linoleic acid, Myristic acid, Oleic acid, Palmitic acid, Vitamin B2, Vitamin B3, Vitamin D3 and Vitamin E. Milk also contains various growth factors such as insulin-like growth factor (IGF-1).
The role of milk and dairy products in cancer, however, lacks clarity.
Is milk good or bad for cancer patients?
Can I eat large amounts of dairy products without worrying about cancer?
Will milk and dairy products increase the risk of cancer?
These are some of the common queries that float around on the internet. A steady increase in milk and dairy product consumption over the past few decades has also drawn the attention of researchers across the world. Hence, different observational studies were carried out to study the association of milk and dairy products with cancer risk. However, the findings of these studies are not consistent. While some of the studies reported a modest increase in the risk of certain cancers, inverse results were observed in few other cancer types.
This blog summarizes some of the recent studies related to the link between milk and dairy products consumption and the risk of cancers.
Can Milk and Dairy Product Consumption increase Cancer Risk?
As we all know, the risk of cancer is strongly influenced by our diet. The key active compounds present in the food that we consume may either increase or decrease the risk of specific types of cancers. When it comes to the association of milk and dairy products with cancer, some of the compounds such as insulin-like growth factor (IGF-1), calcium, vitamin D, casein, lactose, lactoferrin, lactic acid producing bacteria, and dairy lipids are in spotlight .
Let us now zoom into the recent studies which evaluated the association between milk and dairy product consumption and the risk of different types of cancers.
Association of Milk and Dairy Products Intake with Colorectal Cancer Risk
Study done in Chinese Population
In a very recent case-control study published in 2020, the researchers from the Sun Yat-sen University in China evaluated the effects of dietary vitamin D, Calcium and dairy products intakes on colorectal cancer risk in Guangdong, China. Data for the analysis was obtained from 2380 patients with colorectal cancer and 2389 sex and age-matched controls who were recruited for the study between July 2010 and December 2018. (Xin Zhang et al, Br J Nutr., 2020)
The study found that higher dietary intakes of vitamin D and Calcium reduced the risk of colorectal cancer by 43% and 52% respectively. The researchers also found that, compared to those who rarely consumed dairy products, people who consumed high amounts of dairy products were associated with a 61% reduced risk of colorectal cancer risk. Also, those who drank milk had a 48% reduced risk of colorectal cancer than those who did not.
This study provided evidence that high consumption of dietary vitamin D, Calcium, milk and dairy products may be good for reducing colorectal cancer risk in Chinese population.
Study done by the Researchers in Spain
In a study published by the researchers from the Universitat Rovira i Virgili and Instituto de Salud Carlos III (ISCIII) in Spain, they did a systematic review and meta-analysis to examine the associations between dairy product consumption and colorectal cancer incidence using data from 15 population based and 14 case-control studies involving more than 22,000 cases. Following were the key findings of the population based studies. (Laura Barrubés et al, Adv Nutr., 2019)
- A higher consumption of total dairy products and milk was associated with a consistent significant decrease in colorectal/bowel risk, with the risk reduced by approximately 18%, as compared with those with lower consumption.
- There was significant protective association between low-fat milk consumption and colorectal cancer, with the risk reduction of approximately 27%; however, this association was observed only for colon cancer.
- Intake of cheese may reduce the risk of colorectal cancer by 15% and proximal colon cancer by 26%.
- No significant associations with colorectal cancer were found for the consumption of low-fat dairy products, whole milk, fermented dairy products, or cultured milk.
However, most of these associations were not supported by the case-control studies.
In short, when the researchers evaluated the association between different types of dairy products and colorectal cancer location, they found that:
- Higher consumption of total dairy products and total milk was associated with a lower risk of developing colorectal cancer at any anatomic location
- Low-fat milk consumption was associated with a lower risk of colorectal cancer only in colon cancer.
- Cheese consumption was associated with a reduced risk of colorectal cancer, particularly, proximal colon cancer.
The researchers suggested more well designed clinical trials to confirm these findings.
Study in an Older Mediterranean Population at High Cardiovascular Risk
Another observational study done by the researchers from different Universities in Spain evaluated the association between the consumption of total dairy products, their different subtypes and colorectal cancer risk in older Mediterranean individuals who were at high cardiovascular risk. The researchers analyzed data from 7,216 men and women who were aged between 55 and 80 years and did not have Colorectal cancer when recruited in the PREvención con DIeta MEDiterránea study between 2003 and 2009. These patients were followed up until December 2012. During a mean follow-up of 6.0 years, a total of 101 colorectal cancer cases were reported. (Laura Barrubés et al, Int J Cancer., 2018)
The study found that compared to those with lower intakes, people with higher intakes of dairy products and low-fat milk consumption had a 45% and 46% reduced risk of colorectal cancers, respectively. Hence, intake of low-fat milk and dairy products may be good for reducing the risk of colorectal cancer.
Study in Middle Eastern and North African Countries
A study done by the researchers from the Sidi Mohamed Ben Abdellah University and Laboratory of Microbiology and Molecular Biology in Fez, Morocco evaluated the association between consumption of dairy products and the risk of colorectal cancer in the Middle Eastern and North African countries (MENA). Data for the analysis was obtained from 7 studies which were obtained through literature search for studies published till the 31stof December 2016 in PubMed, Clinical Trials, and Cochrane. (K El Kinany et al, BMC Cancer., 2018)
Overall, the study found no significant association for dairy products. Evaluation of association with modern dairy products obtained conflicting results. The study also found an increase in colorectal cancer risk with increased intake of traditional dairy products. However, they found that higher intakes of calcium was associated with a reduced risk of colorectal cancer risk.
The results of this study were inconsistent. Hence, the researchers suggested further studies to understand the association between colorectal cancer risk and dairy products consumption in the Middle Eastern and North African countries.
Association of Non-fermented Milk, Solid Cheese, and Fermented milk with Colorectal Cancer Risk
Researchers of the Monash University in Australia did a systematic review and meta-analysis of 15 population based studies involving over 900,000 subjects and over 5200 colorectal cancer cases, to evaluate the association between intake of different types of dairy foods such as non-fermented milk, solid cheese, and fermented milk during adulthood and the development of colorectal cancer. Following were the key findings of the study. (Robin A Ralston et al, Crit Rev Food Sci Nutr., 2014)
- There was a 26% reduced risk of colorectal cancer in men consuming high amounts of non-fermented milk averaging 525 g/day, when compared to those with low intakes of non-fermented milk.
- There was no association between consumption of nonfermented milk and rectal cancer in men or non-fermented milk and colon or rectal cancer in women.
- High consumption of solid cheese or fermented milk did not reduce the risk of colorectal cancer in this cohort.
Hence, higher intake of nonfermented milk may be good for reducing the risk of colon cancer in men.
Key take-away on the Association between Milk and Dairy product Consumption and Colorectal Cancer Risk : Although in few studies, there are conflicting results, most of the studies indicate that consuming milk and dairy products may be good for reducing the risk of colorectal cancer or bowel cancer. This protective effect may be attributed to the high calcium content in milk and dairy products, casein and lactose which increases the bioavailability of calcium, lactic acid producing bacteria, lactoferrin, vitamin D, conjugated linoleic acid and short chain fatty acid butyrate. (World Cancer Research Fund)
Association of Milk and Dairy Products Intake with Prostate Cancer Risk
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WCRF/AICR Continuous Update Project
In the WCRF/AICR Continuous Update Project, the researchers from the Norwegian University of Science and Technology in Norway, Imperial College in London and University of Leeds in UK evaluated the association between the intake of calcium and dairy products and prostate cancer risk, based on 32 studies obtained through literature search in Pubmed till April 2013. (Dagfinn Aune et al, Am J Clin Nutr., 2015)
The study found that the intakes of total dairy products, total milk, low-fat milk, cheese, and dietary calcium were associated with an increased risk of total prostate cancer. They also highlighted that this association was true for only total calcium and dairy calcium intakes, but not for non-dairy calcium or calcium supplement intakes. The study found that supplemental calcium intake was associated with an increased risk of fatal prostate cancer.
Dairy Products Intake and Prostate Cancer Mortality Risk
A study published in 2016 by the researchers from the Zhejiang University in China evaluated the association between dairy products intake and cancer mortality risk based on data from 11 population-based cohort studies involving 778,929 individuals, obtained through literature search in PubMed and EMBASE. (Wei Lu et al, Nutr J., 2016)
The study found that there was no association between total dairy products intake and mortality risk due to cancer, when all cancers were considered together. However, they found that a high consumption of whole milk (dairy) in men may not be good as it may increase the risk of deaths due to prostate cancer significantly.
Association between Plant and Animal-Based Foods (including Dairy products) and Prostate Cancer Risk
A study published in the Journal of the American Osteopathic Association in 2019, by the researchers from the Mayo Clinic in Rochester, Minnesota evaluated the association between plant and animal-based food (including dairy products) consumption and prostate cancer risk. The study included data from 47 references including 2 very large cohort studies with more than 100,000 participants, 6 large cohort studies with more than 40,000 participants, 11 medium cohort studies with more than 10,000 participants, 10 small cohort studies with less than 10,000 participants, 13 case-control studies, 4 meta-analyses, and 1 population study which investigated the association between diet and prostate cancer risk. (John Shin et al, The Journal of the American Osteopathic Association, 2019)
The analysis found that consumption of plant-based foods either decreased or did not change the risk of Prostate cancer, however, intake of animal-based foods, particularly dairy products either increased or did not change the risk of Prostate Cancer.
Key take-away on the Association between Milk and Dairy Product Consumption and Prostate Cancer Risk : Most of the observational studies elaborated above suggested that a very high consumption of milk and dairy products may be associated with an increased risk of prostate cancer or prostate cancer deaths. Conversely, there are few studies that do not support the findings on the harmful impact of dairy consumption on overall prostate cancer risk, especially among men in the United States (Isabella Preble et al, Nutrients., 2019) Hence, more clinical studies may be required to confirm whether milk intake is good or bad for prostate cancer, before recommending men to avoid milk and dairy product consumption.
In any case, the possibility of increased risk of prostate cancer through dairy consumption may be attributed to various factors such as calcium, Vitamin-D and IGF-1. Higher consumption of milk and dairy products increases calcium levels which may reduce the formation of biologically active forms of vitamin D resulting in increased prostate cancer cell proliferation. Higher consumption of milk and dairy products may also modestly increase circulating concentrations of IGF-1 which is a risk factor for prostate cancer. (World Cancer Research Fund)
Association of Milk and Dairy Products Intake with Breast Cancer Risk
Association between Dairy Intake and Breast Cancer in Western and Asian Populations
A study done by the researchers from the Shanghai Municipal Center for Disease Control and Prevention, Shanghai Armed Policed General Troops Hospital, and Affiliated Nanshan Hospital of Guangdong Medical College in China and University of North Carolina at Chapel Hill in the US evaluated the association between dairy consumption and breast cancer risk based on data from 22 prospective cohort studies involving 1,566,940 participants and 5 case-control studies involving 33,372 participants. Following were the key findings of the study. (Jiajie Zang et al, J Breast Cancer., 2015)
- Intake of 400-600 g or more dairy per day significantly reduced the risk of breast cancer, when compared with low dairy consumption (<400 g/day).
- Yogurt and low-fat dairy, but not other dairy products reduced the risk of breast cancer.
- People with high intakes of dairy in the United States had a risk reduction of 9%; and in those followed for more than 10 years, the risk reduction was 10%.
- Asians with the highest intakes of dairy were associated with a 26% reduced risk of breast cancer compared to those with low dairy intake.
In short, this study suggested that high dairy consumption may reduce the risk of developing breast cancer and the effect was dependent on the dose, dairy-type, and time.
Health Examinees-Gem (HEXA-G) study
Researchers from the Seoul National University in Korea evaluated the association between dairy milk consumption and the risk for breast cancer based on dietary data from 93,306 participants aged between 40-69 years who were recruited in the Health Examinees-Gem (HEXA-G) study between 2004 and 2013. During a mean follow-up of 6.3 years, a total of 359 breast cancer cases were reported. (Woo-Kyoung Shin et al, Nutrients., 2019)
The study did not find any association between milk consumption and decreased risk for breast cancer when the whole group of participants was considered together. However, they found that among Korean women under 50 years of age, those who consumed more than 1 servings of dairy milk per day had a 42% reduced risk of breast cancer compared to those who never or rarely consumed milk (<1 serving/week).
Dairy, Soy, and Risk of Breast Cancer
While there a few studies like the ones mentioned above which suggested a possible protective effect of milk consumption on the risk of breast cancer, few other studies such as a very recent study published by the researchers from the Loma Linda University in the US in 2020, found an increased risk of breast cancer in women with high intake of milk. The cohort study included 52,795 North American women with a mean age of 57 years who were initially free of cancer and were followed up for 7.9 years, during which 1057 breast cancer cases were reported. (Gary E Fraser et al, Int J Epidemiol., 2020)
The study found no clear associations between soy based milk and milk products intake and breast cancer, independent of dairy. However, higher intakes of dairy calories and dairy milk increased the risk of breast cancer by 22% and 50%, respectively, when compared to low intakes of milk. The risks were similar in participants who consumed full-fat milk, reduced-fat or non-fat (skimmed) milk. However, no important associations were noted with fermented milk products such as yogurt and cheese.
The study also predicted a marked reduction in breast cancer risk when dairy milk was substituted with soy milk.
Key take-away on the Association between Milk and Dairy Product Consumption and Breast Cancer Risk : So far, there is limited evidence suggesting a protective effect of dairy milk intake against breast cancer risk in premenopausal women. Due to inconsistent results, more studies are needed to test this association. A possible protective effect of milk on breast cancer development may be hypothesized due to high concentrations of conjugated linoleic acids, obtained from milk (apart from calcium and Vitamin-D), which may inhibit mammary tumor development, as found in experimental studies.
Dairy Product Consumption and the Risk of Non-Hodgkin Lymphoma
Researchers from the Medical College of Qingdao University in China conducted a meta-analysis of studies from 16 articles to evaluate the association between dairy product consumption and the risk of Non-Hodgkin Lymphoma. Data for this study was obtained through literature search in PubMed, Web of Science and Embase for relevant articles published till October 2015.
The study found that the risk of Non-Hodgkin Lymphoma increased by 5% and 6% for every 200g increment of dairy product and milk consumption per day, respectively. The researchers also found significant associations between the consumption of total dairy product and milk and an increased risk of diffuse large B-cell lymphoma (DLBCL).They highlighted that dairy product consumption, but not yogurt, may increase the risk of Non-Hodgkin Lymphoma. (Jia Wang et al, Nutrients., 2016)
Conclusion
There is strong evidence that milk and dairy product consumption may reduce the risk of colorectal or bowel cancers. As you may wonder, very high intake of milk and dairy products regularly may not always be safe due to its increased saturated fat content and may be associated with different health issues. Limited evidence suggests that those who consumed large amounts of milk and dairy products are at risk of prostate cancer and Non-Hodgkin Lymphoma. Also, there is limited evidence suggesting a protective effect of dairy milk (containing calcium, vitamin D and conjugated linoleic acid) intake against breast cancer risk. Few studies also found an increased breast cancer risk with milk consumption. Again, due to conflicting and inconsistent results, more studies are needed to test this association.
The association between milk/dairy product intake and risk of different types of cancers may be attributed to the key compounds present in milk such as calcium, Vitamin D, conjugated linoleic acid and growth factors such as IGF-1. Until we have more clarity on the association with cancer risk, it would be better to avoid excessive consumption of milk and dairy products to reduce health issues. Also, instead of avoiding milk and dairy products completely, reducing their number of servings per day would be good to stay away from the possible risk of cancers such as prostate cancer.
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