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Men who have a higher consumption of dairy foods, especially milk, face a significantly increased risk of prostate cancer compared to men who eat less dairy.
This has been seen in a study conducted by researchers at the Loma Linda University School of Public Health, which, on the other hand, found no relationship between increased risk of prostate cancer and non-dairy calcium intake, which suggesting that substances other than calcium play a role in the risk of dairy foods for prostate cancer.
“Our results add to other evidence linking dairy, rather than non-dairy calcium, as a modifiable risk factor for prostate cancer,” said Gary Fraser, principal investigator of the study and professor in the College of Medicine and Loma Linda University School of Public Health.
The results reveal that men who consumed about 430 grams of dairy per day (1 ¾ cups of milk) faced a 25% increased risk of prostate cancer compared to men who ate just 20.2 grams of dairy per day (1/2 cup of milk per week). In addition, those who consumed about 430 grams of dairy per day faced an even greater increased risk compared to men who did not consume any dairy in their diet.
Fraser noted that the results of the study published in the American Journal of Clinical Nutrition presented a minimal variation when whole milk intake was compared with that of reduced or skimmed milk; no significant associations were seen with cheese and yogurt.
The study evaluated the dietary intake of more than 28,000 North American men with a wide range of dairy and calcium exposures, all of whom were initially free of cancer. Dietary intake was estimated from food frequency questionnaires (FFQs) and repeated 24-hour recalls. A baseline questionnaire included demographicsfamily history of prostate cancer, physical activity, alcohol use, prostate cancer screening, and BMI.
Next, the researchers used the state cancer registries to follow the participants’ prostate cancer status for an average of almost eight years. At the end of the study period, state cancer registries reported 1,254 new cases of prostate cancer among participants during follow-up.
As part of their analysis, Fraser said he and his co-authors separated non-dairy calcium intake (from nuts, seeds, cruciferous vegetables and other green vegetables, legumes, fruits and fortified cereals) from intake of dairy foods.
They used a statistical model to focus on dairy food intake, regardless of other factors such as non-dairy calcium intake, family history of prostate cancer, race, or age.
An interesting factor to note, Fraser says, is that the results did not show a uniform increase in risk in men with increased dairy intake. In other words, increasing dairy intake in 50-gram increments did not produce the same increases in risk as portion sizes became larger.
“Most of the continued increased risk occurs at 150 grams, about two-thirds of a glass of milk per day,” says Fraser. “It’s almost as if some biological or biochemical pathway gets saturated at about two-thirds of a cup of milk a day.”
Previous studies may have missed the curvilinear effect or the non-uniform increase in risk between dairy consumption and prostate cancer if most of those participants already drank more than one glass of milk a day. However, this study’s cohort allowed the researchers to compare a wide range of dairy consumption, including very low levels.
The data provided little evidence for an association between calcium intake and incident prostate cancer. “One interpretation is that dairy foods, or some closely associated unknown risk factor, are causally related to prostate cancer risk,” the study stated.
Fraser said that possible reasons for these associations between prostate cancer and dairy milk could be the content of dairy milk sex hormones. Up to 75% of dairy cows are pregnant, and prostate cancer is a hormone-responsive cancer. In addition, previous reports have associated dairy and other animal protein intake with higher blood levels of a hormone, insulin-like growth factor-1 (IGF-1), which is thought to promote certain types of cancer, including the prostate.
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