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Four cups of coffee a day 'halves' mouth cancer risk

“Drinking coffee halves the risk of mouth cancer – even in smokers and drinkers,” claims the Daily Mail.

This story is based on a large US study that found that adults who reported drinking more than four cups of caffeinated coffee a day had a 49% lower relative risk of dying from mouth and throat cancer than those who reported drinking no or occasional caffeinated coffee.

The risk reduction was independent of well-established risk factors for these types of cancer, such as smoking and alcohol intake. Sadly, for tea lovers, a similar risk reduction was not seen for the nation’s favourite beverage.

But before you start thinking that a full Starbucks or Costa loyalty card will allow you to smoke and drink with impunity, it is important to stress a number of points:

  • The risk of developing or dying from other types of cancer was not assessed in this study, nor was the risk of alcohol-related diseases such as liver failure. Smoking and excess alcohol consumption are well-known to cause premature death from a variety of diseases.
  • The study participants were predominantly white, middle aged or elderly and well-educated. Therefore, results may not be consistent in other groups.

Taking into account these limitations, this is an interesting piece of research that raises the possibility that coffee may contain biologically active compounds that have a protective effect against some forms of cancer. But a great deal of further research is required into the exact mechanisms of coffee’s protective effects, if they exist.

Where did the story come from?

The study was carried out by researchers from the American Cancer Society in collaboration with other US universities. It was funded by the American Cancer Society.
 
The study was published in the peer-reviewed American Journal of Epidemiology.

The Daily Mail’s reporting of this study was broadly accurate.

What kind of research was this?

This study examined associations of caffeinated coffee, decaffeinated coffee and tea intake with deaths from oral or pharyngeal cancer in the Cancer Prevention Study II. This is a prospective US cohort study that was begun in 1982 by the American Cancer Society.

The researchers state that previous studies have linked coffee intake to a reduced risk of oral or pharyngeal cancer and that they wanted to explore this relationship further.

Oral cancer, or mouth cancer, is when abnormal cells, known as a tumour, develop on the surface of the tongue, mouth, lips or gums. Less commonly, it can occur in the salivary glands, tonsils and part of the throat leading to the windpipe known as the pharynx (this is known as pharyngeal cancer).

A cohort study collects information on potential risk factors (such as smoking status, coffee intake and other lifestyle behaviours) from people over an extended period of time and documents what diseases they then develop or die from.

Researchers then look to see if there are relationships between death and disease and the potential risk factors documented previously. The major strength of this type of study is that the risk information is collected before the disease or death occurs and so it eliminates the possibility of reverse causality, which can affect other study types such as cross sectional studies.

What did the research involve?

A total of 968,432 US men and women who were free of cancer were analysed in this study. They were drawn from a pool of the Cancer Prevention Study II, which is a prospective cohort study of mortality among 1,184,418 men and women in the United States that was begun in 1982 by the American Cancer Society. The average age of this cohort was 57 years at enrolment.

At enrolment (in 1982) participants completed a self-administered mailed questionnaire, which included demographic characteristics (such as age and gender), personal and family history of cancer and other diseases, and lifestyle and dietary habits. Participants were asked to give their current and previous daily amounts of several types of non-alcoholic beverages, including caffeinated coffee, decaffeinated coffee and tea. These were the main variables of interest in this research.

Participants were also asked to report their previous amounts if their drinking habits of any of these beverages had changed in the previous 10 years.

Daily intake of these beverages was further categorised as:

  • less than one cup of coffee a day (one cup = 237ml)
  • 1–2 cups a day
  • 3–4 cups a day
  • more than four cups a day

Those where this information was missing were excluded as were those who reported drinking “excessive amounts of coffee” (defined as greater than 20 cups a day).

Those with cancer at enrolment or missing information on smoking status were also excluded.

Deaths occurring between enrolment and December 31 2008 were recorded through a combination of personal enquiry and automatic notification from a national death index. Deaths from oral or pharyngeal cancer were defined as those who died during follow-up with cancer of the oral cavity, oropharynx (the part of the throat seen right at the back of the mouth) or hypopharynx (slightly lower down, where the throat connects to the food pipe) using a widely used disease classification system (ICD9 and ICD10). Deaths due to cancer of the lip, nasopharynx (right at the back of the nose) and salivary glands were excluded.

After all exclusions, a total of 968,432 men and women were eligible for analysis. The statistical analysis was appropriate and compared the relative risk of death due to oral or pharyngeal cancer and how it related to daily intake of the beverages of interest. The analysis adjusted for an extensive list of factors that may have influenced the relationship of interest. These included various demographic measures, lifestyle behaviours and family history of disease.

What were the basic results?

Among 968,432 men and women who were cancer-free at enrolment, 868 deaths due to oral or pharyngeal cancer occurred during 26 years of follow-up. Hence, 0.09% of the group died from oral or pharyngeal cancer over the 26 years.

Intake of more than four cups of caffeinated coffee a day was associated with a 49% lower relative risk of oral or pharyngeal death compared with no or occasional caffeinated coffee intake (relative risk (RR) 0.51 95% confidence interval (CI) 0.40 to 0.64).

Consuming more than two cups a day of decaffeinated coffee decreased the risk of oral or pharyngeal death by approximately 39%, but the estimate fell just short of statistical significance (relative risk 0.61, 95% CI 0.37 to 1.01).

A dose-related decline in relative risk was observed with each single cup per day consumed. This means that for every extra cup per day consumed the risk of death from oral or pharyngeal cancer reduced proportionally. The association was independent of the effects of gender, smoking status or alcohol use and no association was found for tea drinking.

How did the researchers interpret the results?

The researchers concluded that caffeinated coffee intake was “inversely associated with oral or pharyngeal cancer mortality” and that “research is needed to elucidate biologic mechanisms whereby coffee might help to protect against these often fatal cancers”.

Conclusion

This large prospective study suggests that the risk of death from oral or pharyngeal cancer is approximately 50% lower in men and women who consume more than four cups of caffeinated coffee a day compared with those who drink no or occasional caffeinated coffee. These associations were independent of gender, smoking status or alcohol use (well established risk factors for oral or pharyngeal cancer) and similar effects were not seen for tea intake.

A similar association was suggested for decaffeinated coffee intake but this fell just short of statistical significance, which means it may have been the result of chance.

There are several limitations associated with this study worth considering. The study participants were predominantly white, middle aged or elderly and well educated; therefore, results may not be consistent in other groups who may have different cancer risk profiles.

The primary outcome was death from oral or pharyngeal cancer. This differs from many other studies in the past which have looked at the risk of new cases of cancer. Hence, the results of this study aren’t directly comparable with these previous studies. Likewise, only limited conclusions can be made about the influence of coffee on developing cancer from this study alone. It tells us much more about risk of death from this specific cancer rather than the risk of getting it in the first place.

Importantly, this study alone does not tell us about the relationship between coffee and other types of cancer other than mouth or throat cancer (either in terms of getting other types of cancer or dying from them).

The researchers state that coffee contains many biologically active compounds but the exact mechanism by which it may protect against death from oral or pharyngeal cancer is not clear. More research is needed to test which compounds, if any, have this effect.

As the researchers point out: “As one of the most widely consumed beverages in the world, coffee and its effects on human health are of considerable interest”. Theoretically, if a cancer-preventing compound could be identified in coffee this could lead to new treatments for cancer but, at the moment, this is very much speculation.

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