A new study by researchers from Loma Linda University, California-USA has found that men with a higher intake of dairy foods but not nondairy calcium, had a higher risk of prostate cancer!.
Prostate cancer is the most common non-cutaneous cancer in American males and also males in other countries. To date, causal links between dairy, or dietary calcium, and this cancer are considered suggestive but limited.
The study team conducted a cohort study of 28,737 Seventh-day Adventist men in the United States and Canada, of whom 6389 were of black ethnicity. Diet was measured by FFQ (Food Frequency Questionnaires), and 275 male participants also provided repeated 24-hours dietary recalls as a calibration sub-study. Incident cancers were mainly found by matching with cancer registries. Analyses used multivariable proportional hazards regressions and regression calibration for some analyses.
The study findings revealed that in total, 1254 (190 advanced) incident prostate cancer cases were found during an average 7.8 y of follow-up. Men at the 90th percentile of dairy intake (430 g/d) compared with the 10th percentile (20.2 g/d) had higher prostate cancer risk (HR: 1.27; 95% CI: 1.12, 1.43).
Similar findings, comparing the same g/d intakes, were demonstrated for advanced prostate cancers (HR: 1.38; 95% CI: 1.02, 1.88), for non-advanced cases (HR: 1.27; 95% CI: 1.11, 1.45), in black participants (HR: 1.24; 95% CI: 0.98, 1.58), and when excluding vegan participants (HR: 1.22; 95% CI: 1.03, 1.43). Calibrated dairy (g/d) regressions (all participants and all prostate cancers), adjusting for dietary measurement error, found a HR of 1.75 (95% CI: 1.32, 2.32). Comparing 90th percentile intake to zero intakes (uncalibrated), the HR was 1.62 (95% CI: 1.26, 2.05).
There was no evidence of an effect of higher (905 mg/d) compared with lower (349 mg/d) intakes of nondairy calcium (HR: 1.16; 95% CI: 0.94, 1.44).
The study team concluded that men with higher intake of dairy foods, but not nondairy calcium, had a higher risk of prostate cancer compared with men having lower intakes. Associations were nonlinear, suggesting greatest increases in risk at relatively low doses.
The study findings were published in the peer reviewed American Journal of Clinical Nutrition.
The study findings showed that men with higher intakes of dairy foods, especially milk, face a significantly higher risk of prostate cancer compared to men with lower intakes.
The study found no such associations between increased prostate cancer risk and intake of non-dairy calcium including soy products, suggesting substances other than calcium play a role in the risk dairy foods poses for
Corresponding author and principal investigator, Dr Gary Fraser, MBChB, PhD, a Professor at the School of Medicine and School of Public Health, Loma Linda University told Thailand Medical News, “Our findings add important weight to other evidence associating dairy products, rather than non-dairy calcium, as a modifiable risk factor for prostate cancer."
The research findings revealed 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 consumed only 20.2 grams of dairy per day (1/2 cup of milk per week).
The findings also showed that men who consumed about 430 grams of dairy per day faced an even greater increase in risk when compared to men with zero dairy intake in their diets.
Dr Fraser noted that the results had minimal variation when comparing intake of full fat versus reduced or nonfat milks; there were no important associations reported with cheese and yogurt.
The research evaluated dietary intakes of over 28,000 North American men with a wide range of dairy and calcium exposure, all of whom were initially free of cancer.
All dietary intakes were estimated from food frequency questionnaires (FFQ) and repeated 24-hour recalls. A baseline questionnaire included demographics, family history of prostate cancer, physical activity, alcohol consumption, prostate cancer screening, and BMI.
The study team then used cancer state registries to follow up on the participants' prostate cancer status for an average time of nearly eight years. By the end of the study period, state cancer registries reported 1,254 new prostate cancer cases among the participants during follow-up.
The study team as part of their analysis, separated non-dairy calcium intake (from nuts, seeds, cruciferous and other green vegetables, legumes, fruits, and fortified cereals) from dairy foods intake.
The study team also used a statistical model to focus on the intake of dairy foods irrespective of other factors like non-dairy calcium intake, family history of prostate cancer, race, or age.
Importantly, the nature of the large, diverse cohort placed the study team in a solid position to assess these differences.
Dr Fraser added, "Because our study cohort showed a great disparity and divergence of dairy intake and calcium levels, we could ask the question with unusual strength."
He said that one interesting factor to note is that results did not show a uniform rise in risk in men with incrementally more dairy intake. In other words, increasing dairy intake by 50-gram increments did not yield the same risk increases as the portions grew larger and larger.
Dr Fraser further added, "Most of the continuing increase in risk is done with by the time you get to 150 grams, about two-thirds of a cup of milk per day. It's almost as if some biological or biochemical pathway is saturated at about two-thirds of a cup of milk per day."
Numerous past studies may have missed the curvilinear effect or non-uniform rise in risk between dairy consumption and prostate cancer if most of those participants already drank more than one cup of milk per day. However, this study's cohort allowed researchers to compare an extensive range of dairy consumption, including very low levels.
Interestingly study data provided little evidence of an association between calcium intake and incident prostate cancer.
The study team commented, "One interpretation is that dairy foods, or some closely associated unknown risk factor, are causally related to the risk of prostate cancer.”
Dr Fraser said the possible reasons for these associations between prostate cancer and dairy milk might be the sex hormone content of dairy milk.
It should be noted that up to 75% of lactating dairy cows are pregnant, and prostate cancer is a hormone-responsive cancer. Further, prior reports have associated intake of dairy and other animal proteins with higher blood levels of a hormone, insulin-like growth factor-1 (IGF-1), which is thought to promote certain cancers, including prostate.
A previous study from Adventist Health Study-2 about the effects of dairy on breast cancer risk in women reported similar results both in the non-uniform risk with increased consumption levels and in the magnitude of risk.
Dr Fraser added, "The parallels between our breast cancer in women paper a year ago and this paper relating to men, are striking. It seems possible that the same biological mechanisms are at work."
However, Dr Fraser says this study does not yet conclusively indicate that milk causes prostate cancer.
Dr Fraser advised that as further studies investigate how dairy consumption could increase prostate cancer risk, prudent men with a family history of prostate cancer or other risk factors would "be cautious" about consuming even moderate levels of dairy milk as part of their diet until this is clarified.
He said, "If you think you're at higher-than-average risk, consider the alternatives of soy, oat, cashew, and other non-dairy milks.”
Thailand Medical News would like to add that coincidentally, the incidence of breast cancer, prostate cancer, colon cancer, rectal cancer, throat cancer, oral cancer, neck cancer, lung cancer, liver cancer and brain cancer is increasing exponentially with the advent of the COVID-19 pandemic.
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