Summary of Vol 102 Issue 11 Interview Transcript
Kristine Crane: Studies on diet and cancer risk have traditionally focused on solid foods, but some studies have begun looking at beverage intake and cancer risk especially with the increase in sweetened beverage intake primarily in the United States and Europe. The role of caffeine has also been widely studied. A study published in Issue 11 of the Journal of the National Cancer Institute looks at 13 cohort studies on caffeinated beverage intake and colon cancer risk. I spoke with Dr. Cynthia Thomson, the coauthor along with Maria Elena Martinez of an editorial about the study.
Kristine Crane: So this study showed that there was no direct association between caffeinated beverage intake and colon cancer risk.
Cynthia Thomson: Well they've found no association with coffee or sweetened beverage intake in colon cancer risk, but overall they did see an association with tea, a slight increase in risk, which surprised them because most of the previous data had suggested that tea was protective against colon cancer and of course there are a number of reasons why they may have found that.
Kristine Crane: Could you talk a little bit about some of the reasons that might account for that associated risk?
Cynthia Thomson: Yeah, so there are a few things. Historically, or over the last 20 years or so when we've looked at tea intake and cancer risk and in particular colon cancer risk, many of the studies that have been done have come out of Asian countries because there is such a high prevalence of tea consumption in those areas, both in terms of lifelong exposure to tea as well as frequency of intake and the amount of intake. And so there in those populations, pretty consistently we've seen that green tea may be protective. On the other hand, this pooled analysis, the studies that were selected, actually there were 13 in all that were looked at in relation to tea and what you find there is that these populations are primarily drawn from the United States and from Europe and so the assumption would be that the tea intake in Europe and the U.S. would be different in that it's more likely to be black tea, probably close to 90 percent of it would be assumed to be black tea.
Cynthia Thompson: Now they weren't able in this analysis to qualify the type of tea, so we don't know that for sure, but it seems that one reason why we may see a different risk profile may be the fact that it was black versus green tea. Another is that just the absolute consumption of tea is a very different habit in Asian countries than in the U.S. and Europe in that in the U.S. and Europe when people consume tea it's not unlikely that they would be drinking the tea and at the same time consuming some kind of pastry or some sweet breakfast food. Whereas in Asian countries where we see a protection from green tea, they're drinking that throughout the day with an overall lower fat, higher plant based diet, just a generally more cancer preventive diet.
Kristine Crane: Was there anything else in this study that was particularly surprising, the fact, for example that sweetened beverages, soft drinks are not associated with colon cancer when sugar might possibly feed cancer?
Cynthia Thomson: So I think there's a couple issues there. One is, does sugar feed cancer? If you put something in cell culture, a cancer cell and you give it sugar, yes. But does that really exemplify what's happening in a human body? We don't think so. On the other hand, if people consume a diet high in sugar and they have any level of insulin resistance or pre diabetes or diabetes itself then there is a concern that that sugar exposure would kind of put them over the edge in terms of running up the insulin levels and insulin is definitely tumor promoting.
Cynthia Thompson: So you have to kind of look at the bigger picture. I think in this case what may have happened-- I mean, yes, I would think that sweetened beverages at high consumption levels in an insulin resistance group would promote colon cancer and would be a concern. But in this pooled analysis, only a small number of people even drank at the high levels. Two percent of people drank more than 18 ounces a day. The upper end of intake of exposure that they looked at was 12 ounces a day. And so 12 ounces a day is not very much. It also is what I would expect during this time period in this age group of people. But you have to realize that you and I, when we think about sweetened beverage exposure, we're thinking about the people who consume 64 ounce Big Gulps or whatever they're called and people who've been doing it from a very young age, maybe even had soda in their baby bottle. And so you can look at this study in terms of if older people drink 12 ounces a day there's no increased risk, but I don't think that it gives us much information in terms of today's population of young people who have grown up on higher levels of soda intake over a lifetime and what their risk may be. So this is something we really need to continue to evaluate over time and see what happens to the population risk over time.
Kristine Crane: I feel like we hear a lot of risk reviews about caffeine intake and cancer risk. What are the risks and benefits of caffeine that we're fairly certain about?
Cynthia Thomson: One thing I want to clarify is this study that was done, this pooled analysis, yes it's looking at beverages and caffeine but really caffeine itself is a very different compound than drinking coffee. In other words, when you and I drink coffee and tea that contain caffeine, we're not drinking caffeine, we're not taking caffeine as a drug almost, which some of the trials have done where they've put in cell culture caffeine and then they've been concerned about the fact that caffeine as a drug given to healthy cells can cause it to mutate and become pro carcinogenic. That is concerning. Is it happening in the human body when we drink caffeine? We don't have a lot of data to suggest that and we get kind of null effect when we look at coffee as the major source of caffeine. So what might be happening is that caffeine may have some detrimental effects in terms of exposure and colon cancer risk but it also may have some beneficial effects that offset those detrimental effects. In other words, obviously coffee beverages don't just contain caffeine, they contain other antioxidant compounds like caffeic acid that may actually protect. So I think when you measure coffee you're not just measuring caffeine and so there may be some pluses and minuses related to that beverage and cancer risk that kind of offset each other and give us these relatively null findings in most of our studies.
Kristine Crane: Is there anything else that you'd like to add?
Cynthia Thomson: I think the other thing that we need to think about in terms of beverages and one of the things I really appreciate about this study is the fact that we are starting to say, "What about beverages?" Historically we've been very focused on people's food intake and really kind of ignored what people do in terms of beverages and yet beverages are accounting for more and more of our total caloric intake. And so one of the things that I think is really important is that we send a message out that we need to pay attention to what we drink, not just in terms of coffee, tea and sweetened beverages but probably diet sodas, juices, all these flavored beverages and smoothies, alcohol. So the one thing that I think is really important is that we do begin to look at this more critically to find out what does beverage do in terms of promoting or protecting against cancer because it is a significant dietary behavior that is modifiable. We could change, we could give people recommendations and we could potentially change their risk profile.
Kristine Crane: That was Cynthia Thomson, Associate Professor of Nutrition at the Arizona Cancer Institute at the University of Arizona. To read her editorial on the cohort study about caffeinated beverage intake and colon cancer risk, look for Issue 11 of the Journal of the National Cancer Institute. You can also follow us on Twitter at jnci_now. This is Kristine Crane at the Journal of the National Cancer Institute.
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