Americans Trust "Test Tube" Science Most, New Survey FindsAmerican Institute for Cancer Research Asked to Rank Scientific Studies Used in Diet-Cancer Research, Public Provides Surprising Answers When it comes to news about diet and cancer risk, Americans say they value test-tube research more highly than human research. This is one surprising finding from a new survey conducted by the American Institute for Cancer Research (AICR). Respondents to the AICR survey were read sample results of diet-cancer studies and asked to rank their importance on a 10-point scale from "Not significant at all," to "So significant I would be highly motivated to change my diet."  When the survey responses were analyzed by type of scientific study, 1 in 4 Americans (27.4 percent) ranked the results of in vitro studies significant enough to change how they eat. Fewer respondents were so convinced by results from the three different types of human studies used to research diet and cancer. Some 21.9 percent said that the findings of a clinical trial would be enough to motivate them to make changes to their diet. Only 20.5 percent deemed the results of case-control studies significant enough to change how they eat, while 20.4 percent said that findings from cohort studies might cause them to rethink their diet. Least convincing of all, according to the surveys, was research involving animal subjects (in vivo studies.) Only 17 percent of respondents said in vivo research would drive them to make changes in their diet. The survey also found that Americans are more likely to find a scientific study convincing if they are informed about its technical details (i.e., type of study, number of subjects, duration.) In the AICR survey, "sound bite" summaries of diet-cancer research were much less likely to motivate dietary change than reports that fully detailed the studies in question. Each Study Type Has Strengths, Weaknesses AICR experts were quick to point out that no single study, however large or well designed, should cause people to change their diets. "Scientific consensus builds slowly," said Dr. Ritva Butrum, AICR Vice-President for Research. "Individual studies may receive a lot of attention, but the public should be aware that each kind of scientific study has inherent strengths and limitations." The reason AICR set out to gauge public reaction to studies of different type was to raise awareness about how each kind of study works. The cancer experts aim to combat widespread frustration about the current state of diet-cancer research. "AICR hears from people every day who are confused by reports that a certain food or food substance seems to prevent cancer one day and has no effect the next," said Dr. Butrum. The cancer researchers believe this frustration grows out of a tendency to view the latest study as the final word, instead of as one piece of a much larger puzzle. "People need to see how the studies fit together. They need to understand what each kind can and cannot do, and why it is vital to always look at the mass of evidence," said Dr. Butrum. Survey Reveals Surprising Hierarchy of Science in Public's Mind When devising the survey, AICR experts had assumed that studies involving human subjects would be generally perceived as more convincing than laboratory research. In particular, they expected that clinical studies would most strongly motivate dietary change. Yet results from the AICR survey suggest that, contrary to popular belief, Americans do not view clinical studies as the "gold standard" of diet-cancer research. Asked to speculate on the reason in vitro research was deemed more convincing than clinical studies and other human research, Dr. Butrum was cautious. "When the public hears that a certain food has prevented cancer in a test tube, they may assume that represents the end of the search, and that a link has been proven. But in vitro results must be supported by checking them against results from in vivo studies, cohort studies, case-control studies, and clinical trials." In vitro studies are used to figure out precisely how and why certain foods or food substances protect against cancer. By zeroing in on the cellular or molecular level, scientists can pinpoint a specific biological chain of events – what researchers call a mechanism – and test it. Results from in vitro studies provide solid evidence that can help researchers devise the animal and human research that will follow. Corroborating results are essential, however, because a cell and tissue study can reveal a food's potential to inhibit or stop the cancer process, but only its potential. In vitro results can't answer important questions such as: Does the observed anti-cancer effect occur within the vastly complex human body? How much of the food is necessary to produce the effect? Is the protective effect diluted or enhanced by other components of the diet? Diet, Cancer Complexities Preclude a Single, "Gold Standard" Approach According to Dr. Butrum, it would be equally incorrect to assume that a clinical trial can prove – or disprove – a specific diet-cancer connection. "Clinical trials are only one method, no better and no worse than any other when it comes to clarifying the diet-cancer link." The clinical trial's popular reputation may have grown in part from its routine use by pharmaceutical manufacturers to test the effectiveness of specific drugs for cancer treatment. Ironically, it is the clinical trial's high degree of specificity that keeps it from being ideally suited to mapping links between diet and cancer prevention. In drug trials, researchers seek to determine the immediate, measurable results of a single substance on cancer patients. Great effort is expended to ensure that neither the researchers nor the subjects know which group of subjects is receiving the cancer drug and which is receiving an inert substance (placebo). After a matter of a few weeks, the trial ends and researchers compare selected biological factors of the cancer patients. Diet-cancer clinical trials generally involve groups of healthy subjects who do not have cancer. This means that researchers must attempt to determine diet's effect on a specific biological factor that they can measure – one that may or may not be related to cancer risk. Because of this, and because cancer is a disease that can take years or decades to occur, finding such a preliminary endpoint to "stand in" for cancer remains controversial. Figuring out how to make diet-cancer trials "blind" – so that neither the researchers nor the subjects know to which group the subjects belong – is also difficult. Any changes the researchers make to the diet of one group will likely be obvious. For this reason, diet-cancer clinical trials tend to involve isolated food substances in the form of a pill. "But people eat food, not food substances," said Dr. Butrum. There is growing evidence from laboratory studies suggesting that nutrients, phytochemicals and other substances within food interact in complex ways to provide protection against cancer. A single-substance clinical trial does not allow for such synergistic effects. Case-Control and Cohort Studies Tie for Third Place In the AICR survey, the two types of studies that are designed to investigate the effect of overall diets upon cancer risk were in a virtual tie for third place. Both case-control studies (20.5 percent) and cohort studies (20.4 percent) gather data on the diets of large groups of subjects and attempt to statistically eliminate many complexities (or confounding factors) to reveal the effect of individual foods upon cancer risk. The main difference between case-control and cohort studies is when they gather data. Case-control studies ask both cancer patients (cases) and a statistically similar group of healthy subjects (controls) to recall their previous diets. Subjects fill out a questionnaire that requires them to estimate what foods they ate, and how often, at a prior time (i.e., before the cancer patients were diagnosed with cancer.) When the reported diets of both groups are compared and analyzed, researchers can say that people who ate certain foods were more or less likely to develop cancer. Because case-control studies are dependent upon subjects' memories, however, certain biases can arise. Many cancer patients make changes to their diets upon being diagnosed, which might make it more difficult to recall previous diets accurately. Recently, scientists have learned that the foods people eat produce consistent bodily changes (called biomarkers) that can be measured, and used to verify the subjects' reported diets. This can help to reduce, but not eliminate, "recall bias." Cohort studies gather data on a large group of healthy subjects and then follow that group over a long period of time, often a decade or more. Periodically (once or twice a year), subjects fill out a follow-up questionnaire about what they eat, and how much, in a typical week. Over time, some of the subjects develop cancer. Researchers then analyze the relationship between subjects' reported diet and their likelihood of developing cancer. Cohort studies offer researchers an opportunity to study healthy people over the extended period of time that cancer develops. When selecting a group of subjects for a cohort study, it is statistically important to include a broad range of diets. In addition, the diets of subjects in cohort studies cannot be easily verified, so this method of studying the diet depends upon a well-designed questionnaire and the accuracy of subjects' self-reported diets. Animal Studies Not Strong Motivators Respondents to the AICR survey were unimpressed by results from diet-cancer studies using animal subjects (in vivo studies). Only 17 percent of respondents said that whether or not a food can prevent cancer in laboratory mice or rats has a bearing on their daily dietary choice. Researchers use animal models to follow up on promising results from cell or tissue studies. In vivo research allows scientists to determine if a particular protective mechanism that has been observed in a test tube also occurs within a complex, living organism. Animals like mice or rats share many biological similarities with humans, including the cancer process itself. Nevertheless, the physiological differences that do exist betweens humans and animals mean that results from animal models can only refine the search and suggest factors for future study. More Details are More Convincing, Americans Say The AICR survey took place in two stages. In the first stage, 1,012 Americans over 18 years old were telephoned at random and asked to rate the significance of five "sound bite summaries" of sample diet-cancer studies. The language for the summaries was modeled on recent "news-in-brief" reports dealing with diet-cancer science. Two weeks later, AICR telephoned a random sample of 1,015 Americans over 18 years old and asked to rate the significance of five sample diet-cancer studies that were described in great detail. The language for the samples was modeled on public information abstracts from cancer studies published in recent scientific literature. In every case, Americans found the detailed reports more convincing than "sound-bites". Respondents were 6.5 percent more likely to rate detailed reports of in vivo studies "so significant I would be highly motivated to change my diet." Additional details increased the public's appreciation for case-control studies by 6.3 percent, for in vitro studies by 6 percent, for cohort studies by 3.1 percent and for clinical studies by 3 percent. Once again, the public's response defied the experts' expectations. In devising the survey, the AICR researchers had predicted that being informed of additional study details would cause Americans to examine the results of a given scientific study more critically. "Our assumption was that the fully detailed reports would help Americans see that each study type possesses inherent limitations in design and in scope, but that didn't happen," said Dr. Butrum. "Clearly, Americans don't yet have the tools they require to see how each new study fits into what has gone before. The need to educate the public about how scientific consensus builds is clearer than ever." ICR Communications conducted the survey for AICR. Complete survey data is available to the press by contacting Glen Weldon at 202-328-7744 x312. Strengths and Weaknesses of Diet-Cancer Studies In vitro studies (cell or tissue culture studies, test tube studies) Strengths: 1. Allow for extremely narrow focus that can pinpoint specific diet-cancer links. Weaknesses: 1. Can only reveal possible mechanisms, cannot establish definite links. In vivo studies (animal models) Strengths: 1. Narrow focus makes it easy to control important variables. Weaknesses: 1. Due to differences between animals and humans, can only reveal possible mechanisms. Case-control studies Strengths: 1. Allow researchers to study effect of overall diet on cancer risk. Weaknesses: 1. Dependent upon subjects' memories of diets eaten years before. Cohort studies Strengths: 1. Allow for the study of the overall diet and cancer risk. Weaknesses: 1. Must involve huge numbers of subjects, eating widely different diets, to be meaningful. Clinical trials Strengths: 1. Unique design allows for elimination of many types of bias that might skew results. Weaknesses: 1. Short-term, highly focused design not suited to complexities of diet or cancer development.
For more information, or to contact American Institute for Cancer Research, see their website at: www.aicr.org |
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