Does Drinking Milk and/or Eating Dairy Products Cause Cancer?
The belief that milk and dairy products cause cancer is largely based on one author’s statement: “Casein is the most relevant chemical carcinogen ever identified, make no mistake about it…we can turn on and turn off cancer, turn on by increasing casein consumption…”1 Casein is a type of protein found in milk and dairy products. The author of the above quote claims that in his experiences, which he described in a book The China Study adding casein to a diet of experimental animals resulted in these animals developing cancer. In fact, he claims that he and his team were able to turn on and/or turn off cancer depending on whether or not they added casein to these animals’ feed.
When evaluating the above claim, it should be first pointed out that, even assuming that casein does have the type of impact on cancer as is described in the above-mentioned book, nobody goes to a grocery store and orders casein. Similarly, nobody has casein as an ingredient in a meal. As mentioned, we ingest casein in milk and dairy products. The notion that these food items cause cancer is based on the assumption that isolated from these products casein has the same impact as casein ingested with these products. This assumption may or may not be correct.
If indeed milk and dairy products cause cancer, because they contain casein, it seems logical that people who ingest more of them should be at a higher risk of developing cancer. Below I have included conclusions from several meta-analyses along with research findings on members of the Seventh-day Adventists (SDA) to see whether this is the case. The following quotes describe the impact of dairy among SDA members: “In AHS-2, we compared study members who were the highest dairy consumers (top 20 percent) to the lowest (bottom 20 percent).…The high dairy consumers had about 70 percent less rectal cancer than the low-consumers, but there was little or no difference for colon cancer. Most of the association of dairy with rectal cancer seemed to come from differences in milk consumption.”2
“Vegan diet seems to confer lower risk for overall and female-specific cancer compared to other dietary patterns. The lacto-ovo-vegetarian diets seem to confer protection from cancers of the gastrointestinal tract.”3 The above-described findings indicate that members of the SDA church who ingest more milk and/or dairy products have a lower risk of some cancers. Thus, these findings do not confirm the suggestion that milk and dairy product consumption causes cancer. It would be more accurate to conclude, based on the findings expressed in the quotes above, that dairy intake leads to a lower risk of some cancers.
Over the years, several meta-analyses that evaluated the impact of milk and/or dairy on cancer diagnosis and mortality have been published. A meta-analysis is a tool to evaluate findings from more than one study to see their cumulative effect on a condition of interest. Below, I am quoting conclusions from available meta-analyses. I purposely have excluded findings from those meta-analyses that were sponsored by the National Dairy Council since this organization directly benefits from the sale of milk and dairy products, thus, it has a conflict of interest when sponsoring research studies.
The first of these meta-analyses was sponsored by the U.S. Department of Agriculture. “Men with the highest intake of dairy products (RR = 1.11 [95% CI = 1.00 to 1.22], P = .047) and calcium (RR = 1.39 [95% CI = 1.09 to 1.77], P = .018) were more likely to develop prostate cancer than men with the lowest intake. Dose-response analyses suggested that dairy product and calcium intakes were each positively associated with the risk of prostate cancer (P trend = .029 and .014, respectively).”4 The findings described in the above quote tell us that men with the highest intake of dairy products had an 11 percent higher risk of prostate cancer (note the RR = 1.11, which is interpreted as 11 percent higher risk, in the above quote), in comparison to men with the lowest intake. We also learned that men with the highest calcium intake had a 39 percent higher risk (note the RR = 1.39, in the above quote), compared to those with lowest intake. Considering that dairy products are among the best dietary sources of calcium we can conclude that they are associated with an increased risk of prostate cancer.
In another meta-analysis, authors evaluated the impact of milk and dairy on cancer of the bladder. It was sponsored by The Natural Science Foundation of Guangdong Province of China. “We extracted data from 14 studies on milk (involving 4879 cases) and 6 studies on dairy products (3087 cases). The total study population was up to 324,241 individuals. Overall, there was no significant association between milk intake and bladder cancer (SRRE 0.89, 95% CI 0.77-1.02). However, an inverse association was found in the United States (SRRE 0.88, 95% CI .79-.99). In addition, no significant association was observed between consumption of dairy products and risk of bladder cancer (SRRE 0.95, 95% CI .71-1.27), though an inverse association was detected in the Japanese population (SRRE 0.56, 95% CI .40-.80).”5 The number 0.88, mentioned in the context of the American study indicates a 12 percent lower risk. Similarly, the number 0.56 indicates a 44 percent lower risk among Japanese. Consistently, the above described findings seem to indicate that milk and dairy may have a protective effect on cancer of the bladder. This conslusion is especially strong among the Japanese.
In yet another meta-analysis, sponsored by The National Institutes of Health, authors evaluated the effect of drinking milk and ingesting dairy products on cancer of the pancreas. Here is what these scientists found: “There was no association between total milk intake and pancreatic cancer risk (MVHR = 0.98, 95% CI = 0.82-1.18 comparing ≥500 with 1-69.9 g/day). Similarly, intakes of low-fat milk, whole milk, cheese, cottage cheese, yogurt, and ice-cream were not associated with pancreatic cancer risk. No statistically significant association was observed between dietary (MVHR = 0.96, 95% CI = 0.77-1.19) and total calcium (MVHR = 0.89, 95% CI = 0.71-1.12) intake and pancreatic cancer risk overall when comparing intakes ≥1300 with <500 mg/day.”6 According to these results there was a negligible 2 percent, not statistically significant, difference among individuals who ingested at least 500 grams of milk and those who ingested about seven times (500/69.9=7.2) less of milk on the development of pancreatic cancer. This means that these findings do not support a suggestion that milk causes cancer.
Findings from the last meta-analysis summarize the impact of dairy products on cancer of the stomach. No sponsor was listed in this publication, which likely means, the authors did the analysis without any financial support. The authors stated, “We found 39 studies that were potentially eligible for inclusion in this meta-analysis, including 10 cohort studies and 29 case-control studies. The summary relative risk for gastric cancer, comparing the highest and lowest dairy product consumption categories, was 1.06 (95%CI: 0.95-1.18).”7 These results indicate a 6 percent increase, which was not statistically significant.
On the basis of available research findings we can conclude that the belief that milk and dairy intake cause cancer is at best very simplified and at worse misleading. Research findings show that milk, dairy products, and calcium intake increase risk of prostate cancer. The same products decrease risk of cancer of colon and rectum. The impact of these products on other cancers is less clear, however, it may be safe to state that they may also decrease risk of cancer of the bladder.
Milk and dairy products have constituted a staple of human diet for millennia. Individuals who want to give up drinking milk and eating dairy products can find at least a few valid reasons to do so. Perhaps the most prominent one has to do with the ethical aspect of keeping cows in confined spaces, treating them with hormones to increase the amount of milk they produce, and giving them unnatural diet that, instead of fresh grass, consists of a mixture of dried, ground dead animals. I myself have become a vegan for these reasons. Adventists should also keep in mind that, according to Ellen White, the time will come when it may not be safe to include milk in our diet.8 However, a concern that by ingesting milk and/or dairy products we may increase risk of getting cancer, with the exception of prostate cancer, seems not to be a valid reason to discard these food items.
Notes & References:
1. Campbell C. Link Between Dairy Protein, Casein, & Cancer. https://www.youtube.com/watch?v=xEWAf6sOGv0.
2. A dairy Conundrum: Does it decrease the risk of colorectal cancer? Adventist Health Study 2 Annual Newsletter. Winter Edition, 2018.
3. Tantamango-Bartley Y., Jaceldo-Siegl K., Fan J., Fraser G. Vegetarian Diets and the Incidence of Cancer in a Low Risk Population. Cancer Epidemiol Biomarkers Prev. 2013;22(2):286-294.
4. Gao X., LaValley MP., Tucker KL. Prospective studies of dairy product and calcium intakes and prostate cancer risk: a meta-analysis. J Natl Cancer Inst. 2005;97(23):1768-1777.
5. Li F., An SL., Zhou Y., Liang ZK., Jiao ZJ., Jing YM., Wan P., Shi XJ., Tan WL. Milk and dairy consumption and risk of bladder cancer: a meta-analysis. Urology. 2011;78(6):1298-1305.
6. Genkinger JM., Wang M., Li R., Albanes D., Anderson KE., Bernstein L., et al. Dairy products and pancreatic cancer risk: a pooled analysis of 14 cohort studies. Ann Oncol. 2014;25(6):1106-1115.
7. Sun Y., Lin LJ., Sang LX., Dai C., Jiang M., Zheng CQ. Dairy product consumption and gastric cancer risk: a meta-analysis. World J Gastroenterol. 2014;20(42):15879-15898.
8. White E. Counsels on diet and foods. Review and Herald. 4th ed. 1976.
Roman Pawlak, Ph.D, RD is an Associate Professor of Nutrition at East Carolina University in North Carolina. He is the author of several books including Forever Young. Secrets of Delaying Aging and Living Disease Free, Healthy Diet without Secrets, In Defense of Vegetarianism, and I Am the Lord Who Heals You, and a co-author of Vegetarian Mother and Her Baby.
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