It’s hard to believe, but the American Cancer Society (ACS) estimates that approximately one in eight American men will be diagnosed with prostate cancer. Besides skin cancer, prostate cancer is the most diagnosed cancer in American men and the second leading cause of cancer death in American men.
In 2022 alone, the ACS predicts approximately 268,490 new prostate cancer diagnoses and 34,500 new prostate cancer-related deaths.
Unfortunately, modern medicine still cannot say exactly what causes prostate cancer. Like any other form of the disease, prostate cancer develops at the cellular level due to DNA changes and mutations. Some of these genetic mutations are inherited, but many are not. In fact, the ACS tells us that most prostate cancer-related gene mutations seen in men are not inherited, but acquired at some point in the patient’s life.
So what are some of the identified external risk factors that can make a man more likely to develop prostate cancer? To begin with, to grow old. About 60% of all prostate cancer diagnoses are in men over the age of 65.
Another possible risk factor is obesity. Some research has shown that abdominal obesity is associated with a more aggressive form of prostate cancer. An unexpected factor could also be being widowed. One study even reported that widowed men are more likely to develop an advanced form of prostate cancer.
Now, new research conducted at Loma Linda University and published in the American Journal of Clinical Nutrition identified a new potential dietary risk factor linked to prostate cancer. Keep reading to find out more!
More milk can mean prostate problems
There’s a lot to love about milk. It’s absolutely jam-packed with essential vitamins and minerals, great for bone health, and packs a powerful protein punch to boot. However, the results of this new study indicate that milk consumption is associated with an increased risk of prostate cancer.
The study authors report that men with high habitual consumption of cow’s milk face a significantly higher risk of prostate cancer compared to other men who drink less milk. Specifically, research found that men who drank about 430 grams of dairy products per day (1.75 cups of milk) had a 25% higher risk of prostate cancer than other men who drank less milk daily (about half a cup a week). The risk of prostate cancer in daily milk drinkers was even higher than in men who avoided dairy altogether.
Calcium has been linked to prostate cancer in the past, and dairy products like milk contain tons of calcium. Most importantly, the research team claims to have observed no correlation between the increased risk of prostate cancer and the ingestion of non-dairy calcium. In other words, if it’s clear that something in milk is linked to the development of prostate cancer, it’s not just calcium.
“Our results add significant weight to other evidence linking dairy, rather than non-dairy calcium, as a modifiable risk factor for prostate cancer,” says Gary Fraser, MBChB, Ph.D.principal investigator of the study and professor at the School of Medicine and the School of Public Health at Loma Linda University, in a press release.
Interestingly, no association was observed between prostate cancer risk and cheese and yogurt consumption.
Prostate cancer risk peaks around 150 grams of milk a day
The study authors point out that their work did not reveal that the risk of prostate cancer increases indefinitely as more milk is ingested. Risk increases seem to stabilize around two-thirds of a cup of milk per day.
“Most of the continued increase in risk is eliminated by the time you hit 150 grams, or about two-thirds of a cup of milk a day,” says Dr Fraser. “It’s almost as if a biological or biochemical pathway is saturated at about two-thirds of a cup of milk a day.”
Solve the Milk Mystery
As mentioned earlier, this study clearly shows that calcium alone is not responsible for the association between prostate cancer and milk. So what’s going on here?
“One interpretation is that dairy, or some closely associated unknown risk factor, is causally related to prostate cancer risk,” the study says.
Dr. Fraser hypothesizes that sex hormones found in cow’s milk may be involved. Most (up to 75%) lactating dairy cows are pregnant, and prostate cancer happens to be a hormone-sensitive cancer. Additionally, previous research has shown that the ingestion of dairy and other animal proteins is linked to higher levels of a specific hormone in the blood (IGF-1), and IGF- 1 promotes the growth of certain cancers, including prostate cancer.
Milk is also linked to breast cancer
This work ties in well with an earlier study conducted at LLU. This project revealed that the ingestion of cow’s milk is associated with an increased risk of breast cancer in women.
“The parallels between our article a year ago on breast cancer in women and this article about men are striking,” comments Dr Fraser. “It seems possible that the same biological mechanisms are at work.”
The take-out sale
In conclusion, the study authors caution that their results do not confirm that cow’s milk causes prostate cancer, only that there is an association between milk consumption and an increased risk of prostate cancer. . More research is ultimately needed before final conclusions can be agreed.
That being said, researchers still say it’s probably a prudent idea for men with a family history of prostate cancer to think twice before consuming even moderate amounts of cow’s milk.
“If you think you are at above average risk, consider soy, oat, cashew and other non-dairy milk alternatives,” Dr. Fraser concludes.
These results are not based on a small-scale research project. More than 28,000 men living in North America took part in this study, which required an average follow-up period of just under eight years.
All participants were cancer-free at the start of the study, but individual dairy/calcium intake habits varied widely. Some men drank tons of milk, others avoided dairy altogether. Each man’s usual dairy intake was estimated via food frequency questionnaires (FFQs) and 24-hour dietary recalls. In addition, a baseline survey completed by each subject collected demographic data such as BMI, exercise habits, smoking habits, family history of cancer, and any previous screening for prostate cancer.
After all the initial data was collected, the researchers kept tabs on national cancer registries for the next eight years. At the end of the observation period, a total of 1,254 prostate cancer diagnoses were noted among study participants.
The research team took great care to separate non-dairy calcium intake (via nuts, fruits, seeds, legumes, vegetables, etc.) from dairy-related dietary calcium sources. Then, a statistical model was used to analyze the impact of dairy product ingestion independently of any other factors (non-dairy calcium, family medical history, age, etc.)
Overall, the study authors say the approach they took and the large sample population they had to work with puts them in a unique position to research this topic.
“Because our study cohort showed great disparity and discrepancy in dairy intake and calcium levels, we could ask the question with unusual force,” Dr. Fraser adds.
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