A new study, recently presented at the European Association of Urology congress in Barcelona, has homed in on two specific compounds in coffee that may inhibit the growth of prostate cancer. The research has only been demonstrated in animal models at this point, but the discovery may explain why several observational studies in humans found male coffee drinkers often suffer from lower rates of prostate cancer.

A couple of major epidemiological studies in recent years have concluded that, at the very least, moderate coffee consumption is not harmful to most of us, and a few cups a day may even be beneficial. However, despite these massive observational studies finding possible correlations between coffee and improved health, this kind of self-reported data doesn't affirm causation or help us understand exactly how coffee could be beneficial.

So a variety of scientists around the globe are zooming in on particular compounds in coffee and trying to understand what effects they could be having on us. Although caffeine is the most well-known compound in coffee, and demonstrates possible protective heart benefits, there are over a thousand other compounds in the humble cup of joe that could be helping us too.

The new research initially focused on six specific prospective anti-cancer compounds found in coffee. After testing the compounds on prostate cancer cells, two particular compounds stood out for inhibiting cell proliferation in low concentrations: kahweol acetate and cafestol. A follow-up study was undertaken in mice implanted with prostrate cancer cells. Alongside an untreated control group, some animals were treated with either kahweol acetate or cafestol, while others were administered a combination of the two.

"We found that kahweol acetate and cafestol inhibited the growth of the cancer cells in mice, but the combination seemed to work synergistically, leading to a significantly slower tumor growth than in untreated mice," explains Hiroaki Iwamoto, first author on the new research. "After 11 days, the untreated tumors had grown by around 3 and a half times the original volume (342%), whereas the tumors in the mice treated with both compounds had grown by around just over one and a half (167%) times the original size."

Of course, this doesn't mean a person suffering from prostrate cancer should immediately start drinking multiple cups of coffee every day as an anti-cancer measure. The researchers do reasonably note this work has only been established in animal models and needs to be replicated in humans.

The study does establish that the concentrations of these two particular compounds used in the animal study can be replicated in humans by drinking three cups of Turkish coffee or six cups of Mocha coffee. Different extraction techniques do apparently matter here, and it is suggested that filter coffee eliminates these two beneficial compounds from the final product.

Ultimately, perhaps the most promising takeaway from the research is there could be a new prostate cancer treatment pathway for scientists to explore. Consuming multiple cups of coffee a day just to get a suitable dose of kahweol acetate and cafestol is not a hugely viable treatment suggestion for many cancer patients.

"Coffee can have both positive and negative effects (for example it can increase hypertension), so we need to find out more about the mechanisms behind these findings before we can think about clinical applications," says Iwamoto. "However, if we can confirm these results, we may have candidates to treat drug-resistant prostate cancer."

The new study was published in the journal The Prostate.