Researchers to Men With Prostate Cancer: Avoid Whole Milk

Nick Mulcahy

November 15, 2017

Enjoying a tall glass of cold, whole milk on a regular basis is a no-go for men with prostate cancer, advise the authors of a new observational study.

"Men with non-metastatic prostate cancer who choose to drink milk should select non-fat or low-fat options," conclude the authors, led by June Chan, ScD, a professor of epidemiology and biostatistics and of urology, University of California, San Francisco.

They found that whole milk consumption after a prostate cancer diagnosis was tied to an increased risk for recurrence, particularly among overweight men.

However, an expert not involved in the study disagrees with the authors' conclusion about milk, citing insufficient evidence.

Men with prostate cancer who choose to drink milk should select non-fat or low-fat options. Chan et al.

The new study was published online November 6 in The Prostate.

This was a prospective study among 1334 men with nonmetastatic disease participating in the Cancer of the Prostate Strategic Research Endeavor (CaPSURE). Participating men answered a food questionnaire in 2004-2005 (a median of 2 years after their diagnosis). They were followed until 2016 for post-treatment recurrence.

The median follow-up was 8 years. During that time, there were 137 recurrence events, which included biochemical recurrence, metastases, and prostate cancer–related deaths.

Dr Chan and colleagues found that men who were regular milk drinkers (>4 servings a week) had about an 80% increased risk for recurrence compared with infrequent milk drinkers (0 to 3 servings a month; hazard ratio [HR], 1.73; P = .04).

When the researchers looked at the men according to different body mass indexes (BMIs), they found that those who were very overweight and obese had a much greater risk and that the risk disappeared among normal-weight men.

Among the big men (BMI > 27 kg/m2), regular whole milk consumption was associated with a 3-fold higher risk for recurrence when compared with infrequent consumption (HR, 2.96; P < .001).

On the other hand, no tie between milk-drinking frequency and recurrence risk was seen in men with BMI below this cut-point.

Notably, the authors say that the statistically significant interaction between whole milk consumption and BMI may be due to chance.

Medscape Medical News asked Dr Chan if her team's recommendation for  men with prostate cancer to avoid whole milk was perhaps a bit over-restrictive, given the uncertainty about the findings.

"The recommendation that men try to switch to non- or low-fat milk is not solely based on our data or this one study, but was intended to be a broader public health recommendations to consume low-fat dairy products, to minimize saturated fat intake for general health," explained Dr Chan.

This is in line with recommendations for the prevention of heart disease,  which remains the main cause of death in the United States, including for men diagnosed with prostate cancer, she pointed out.

However, a prostate cancer expert had a different take on the study's conclusion.

"I don't think based upon these data we should tell men to avoid whole milk," said Stephen Freedland, MD, co-director, Cancer Genetics and Prevention Program, Samuel Oschin Comprehensive Cancer Institute at Cedars-Sinai Medical Center in Los Angeles, California.

I don't think based upon these data we should tell men to avoid whole milk. Dr Stephen Freeland

"I am hesitant to translate observational studies into direct patient advice," he told Medscape Medical News.

Dr Freedland explained that "perhaps to avoid whole milk, men will drink more orange juice, which is high in sugar, which some studies suggest is bad for prostate cancer."

People often consume milk with other foods, he also pointed out: "Perhaps this was related to men eating sugary cereal with their milk and was unrelated to milk intake. Perhaps it is the milk. The point is, we don't know."

Finally, Dr Freedland offered a summary caution: "When we make suggestions to patients, there can often be unintended consequences." 

More on Milk and Prostate Cancer

For the past several decades, academics have studied dairy products in relation to the development of prostate cancer. The results have not been consistent, say both the study authors and Dr Freedland.

However, Dr Chan and colleagues add that the data "generally suggest that dairy products are associated with an increased risk of being diagnosed with prostate cancer."

Less studied has been the relationship between dairy, including milk, and prostate cancer recurrence. There have only been a few studies on the subject.

Previously, Dr Chan and colleagues were the first to report, from the Health Professionals Follow-up Study, that the frequent milk consumers had a twofold increased risk for dying of prostate cancer and a 51% increase in the relative risk for recurrence compared with infrequent consumers (Cancer Epidemiol Biomarkers Prev. 2012;21:428-436).

Also, Swedish researchers recently reported, in a study of men with localized prostate cancer, an elevated risk for disease-specific mortality among men  who drank a lot of milk (3 or more servings a day) compared with men who drank less than 1 serving a day (Int J Cancer. 2017;140:2060-2069).

Other Dairy Foods

In the current study, Dr Chan and colleagues also observed that even though whole milk was associated with an increased risk for prostate cancer recurrence, no such increase was seen with other dairy foods, including butter and ice cream, which are made from whole milk.  

Dr Chan commented on this surprise about dairy foods: "They may not be consumed in the same volume or frequency for us to detect an association at the individual level."

The authors are not sure what physiologic mechanisms may underlie any tie between whole milk consumption and prostate cancer recurrence among overweight men.

"It is possible that overweight and obese men have greater increases in systemic inflammation and insulin resistance when consuming a high saturated fat diet compared to normal weight men, thereby promoting prostate cancer progression," they write.

Dr Freedland believes in summarizing the data with patients: "I will tell them, 'Some studies suggest high whole milk intake may be bad for prostate cancer, but others say it is not.' Let the patient make the decision."

The study was funded by the US Department of Defense Cancer Research Program, National Institutes of Health and the Helen Diller Family Comprehensive Cancer Center at UCSF. The authors and Dr Freedland have disclosed no relevant financial relationships.

Prostate. Published online November 6, 2017. Abstract

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