By Dr. Geoffrey Modest
A working group of the International Agency for Research on Cancer (IARC), the specialized cancer agency of the World Health Organization, reviewed data on the relationship between caffeine as well as hot beverages with cancer, finding that caffeine is good but hot beverages bad (See doi.org/10.1016/S1470-2045(16)30239-X). The full Monograph is in press, but Lancet Oncology published a summary.
- Caffeine had been listed in 1991 as “possibly carcinogenic to humans” based on limited data of increase in bladder cancer. But:
- Bladder cancer: newer, better data (>1000 observational and experimental studies) suggest that there is no consistent relationship, and raised the concern in older studies of potential confounding from cigarettes or occupational exposures.
- Liver cancer: there seems to be an inverse correlation, based on case-control studies, with decreasing risk by 15% for each cup of coffee/day. Beneficial effects on liver fibrosis and cirrhosis
- Breast cancer: meta-analysis of 1 million women suggests no association or ?modest inverse one
- Pancreas and prostate: no increase
- Endometrium: likely inverse associationwith coffee
- Other cancers (lung, colorectal, stomach, esophagus, oral cavity, ovary, brain, childhood leukemia): data inconsistent or not evaluable because of biases, etc.
- Conclusion: “overall coffee drinking was evaluated as unclassifiable as to it carcinogenicity to humans”
- Hot drinks, IARC classified Mate, served traditionally at a very hot temperature (>65°C), as “probably carcinogenic to humans”. Mate is made from dried leaves of Ilex paraguariensis (Mate Yerba) with varying caffeine content and mainly consumed in South America, and less so in Middle East, Europe, North America.
- Esophageal cancer: significantly increased risk, but only when drunk very hot or hot. and similar results have been found for other very hot drinks
- Animal studies: very hot water (65-70°C) increased the incidence of nitrosamine-induced esophageal tumors. And hot water (>65°C) can act as a tumor promoter, perhaps through chronic cell injury
- Conclusion: “drinking very hot beverages at above 65°C was classiﬁed as ‘probably carcinogenic to humans’, but “drinking mate that is not very hot was ‘not classiﬁable as to its carcinogenicity to humans'”
- Good news for those of us who really like or require coffee, as well as coffee growers, who have not been doing so well lately (see http://www.centralamericadata.com/en/article/main/Good_News_for_Coffee?u=29f723785a1c27639a0d8732b32d9c8c&s=n&e=3&mid=[MESSAGEID )
- For prior blogs, see http://blogs.bmj.com/bmjebmspotlight/2016/04/25/primary-care-corner-with-geoffrey-modest-md-coffee-and-decreased-colon-cancer/ which reviews a study finding decreased risk of colon cancer in coffee drinkers, with a dose-response curve. Also this blog refers to others finding decrease in total mortality, decreased coronary artery calcium scores, and one of chocolate decreasing peripheral artery disease.