Black Coffee and Cancer Hype Unsubstantiated

 Judging by many of the papers I see regularly, the pressure to publish must be immense. For publishers and authors, volume is clearly king. If not, then how else to describe the continued publication of food studies with implausibly supportable conclusions, or of exercise intervention studies that conclude the meager number of additional calories burned don’t, gasp, lead to weight loss? By way of example, let’s look at two recent representative studies. 

The first is a subject near and dear to my heart: black coffee. Certainly, my confirmation bias has me wanting to believe anything good I’ve ever read about coffee. So imagine how excited I must have been to read that drinking two or more cups of black coffee (or tea) per day would decrease my risk for cancer and cancer mortality? How will it do that? After reading, it seems neither I, nor the authors, have any idea. 

Looking at their paper, the premise seems to be that the authors believe the data suggesting sugar-sweetened beverages increase cancer risk are solid, and so they set out to study whether there were differences in cancer risk between black coffee and tea drinkers and sugared coffee and tea drinkers (as well as other beverages). To assess how much of each beverage a person consumed, dietary intake was measured by way of anywhere between one and five separate 24-hour dietary recalls administered over an 8.8-year period. 

Setting aside the question of the utility and validity of such recalls in multiyear extrapolation of dietary habits that presumes that what you ate yesterday is representative of what you will eat daily for years, controlling for other dietary intake factors would be crucial in establishing a link between a single dietary item and any health outcome. So, what was controlled for? Not much. Though we all eat hundreds, if not thousands, of different foods and ingredients in who knows how many combinations, aside from beverages, all that was controlled for here were the very broad strokes of “meat intake, fish or seafood intake, vegetable intake, and fruit intake.” 

Then they looked at 27 different types of cancers and 11 different beverages to see if they could find relationships with each and to overall cancer risks, and they concluded that “compared with non-consumers of unsweetened coffee, intake of >2 cups of unsweetened coffee per day was associated with lower overall cancer incidence (HR [hazard ratio]: 0.95; 95% CI: 0.92, 0.98) and mortality (HR: 0.89; 95% CI: 0.83, 0.96).”

Go Team Coffee! But looking more closely through the appendix of supplementary data, the largest protective effect against overall cancer mortality was found among people with diabetes reportedly drinking less than one cup of black coffee per day where their HR for all cause cancer mortality was 0.62, lower than the 0.83 of that same group drinking one to two cups per day, or the 0.82 of that same group drinking more than cups per day. In people without diabetes, they, too, saw a decreased risk when reportedly drinking less than one cup per day, with an HR of 0.83 — which was also lower than those drinking one to two cups daily or more than three cups daily (both at 0.9). 

In all comers, the relationship held with the largest impact on cancer mortality being found among those drinking one cup or less of black coffee a day. Similar results were found with black (unsweetened) tea. Weird then that, again, putting aside the questionable ability to make conclusions about the impact of single food items on a condition as multifactorial as cancer, the authors’ conclusion is that benefits increase with increased black coffee or tea consumption. Meanwhile, this similarly challenged study published 3 months later, but in a different journal, found no impact of black coffee on cancer mortality. 

Suffice to say, I’m going to keep drinking my daily black coffee, but I’m not going to kid myself into thinking there’s good evidence to suggest it’ll increase or decrease my cancer risk.

What I’m not going to do, though, is whole-body vibration therapy (WBVT) to help manage my weight. If you’re wondering what that is, it involves standing, sitting, or lying on a vibrating platform. For us older folks reading this, it’s the modern-day version of the I Love Lucy fat jiggler. Well, guess what? Prepare to be very shocked. A systematic review and meta-analysis of 20 randomized controlled trials found WBVT did not significantly reduce body mass or fat mass. But somehow, that did not stop the authors from concluding, “Future studies should explore optimized WBVT parameters, potential metabolic adaptations, and synergies with other interventions to enhance its applicability in body mass management.” Sigh.

I don’t have an easy fix for publishers or authors. Both should know better, yet both are heavily incentivized to publish. While some papers, like the one on WBVT, are relatively harmless, many of the “magic single food” studies, including the ones discussed above, get amplified by the media and widely publicized. This, in turn, fuels the fire of widespread scientific and nutritional illiteracy, and unfortunately, the consequences of that are anything but benign.

Yoni Freedhoff, MD

Associate Professor, Department of Family Medicine, University of Ottawa; Medical Director, Bariatric Medical Institute, Ottawa, Ontario, Canada

Disclosure: Yoni Freedhoff, MD, has disclosed the following relevant financial relationships:
Serve(d) as a director, officer, partner, employee, advisor, consultant, or trustee for: Bariatric Medical Institute; Constant Health
Received research grant from: Novo Nordisk

https://www.medscape.com/viewarticle/black-coffee-and-cancer-hype-unsubstantiated-2025a1000y6o