- This document only addresses ways to look at information on methods that are said to prevent cancer, but some of the same principles can be used when looking at information on cancer treatment, sympto
- Look at the science behind the prevention method
- Types of human studies on cancer risk
- Studies that observe humans
- Human testing: Clinical trials
- A closer look at the evidence
- Other questions about studies on new ways to prevent cancer
- What does this mean to you?
- To learn more
- Appendix A
Other questions about studies on new ways to prevent cancer
Does the study make sense in light of what’s known about the human body and the way the method affects it?
This question is often called biological plausibility. Does the effect on the body fit with what we already know? For instance, a substance that blocks female hormones may be expected to reduce the risk of cancers that use female hormones to grow. (Of course, whether it would really reduce cancer risk in people would still need to be tested.) But sometimes the researchers may not understand exactly how a substance may work in the body. In cases where little is known about how it may work, evidence from earlier studies may have a role in suggesting what the substance is likely to do in humans.
Does the study support or contradict past studies?
The more evidence there is for a prevention method, the more likely the results are to be true. Sometimes, a study or two will come out that encourages people to believe that a certain food or supplement will reduce cancer risk. Later on, more careful studies often find that the lower cancer risk was due to something else entirely – like chance, age, or healthy habits – and had nothing to do with the food or supplement. This kind of confusion starts most often with observation studies that try to guess the cause for different health outcomes.
Does the study promote something that’s supposed to prevent all cancers?
This goes along with biological plausibility, discussed above. Since there are many different types of cancer, and many are known to be caused or affected by different factors, it’s very unlikely that one method can address all of them. Claims that there’s one method that prevents all kinds of cancer are highly suspect.
Why are most products that are advertised as immune boosters and cancer preventives not approved by the FDA?
There are many herbs and food extracts that are advertised as having an effect on cancer. As long as these food-related products are generally regarded as safe, there are relatively few restrictions on their sales. Many are simply packaged and sold. Because some of these supplements have been found not to contain what’s listed on the label, and others have been found to include substances that were not on the label, the FDA set up rules for dietary supplements that took effect in 2010.
These rules were intended to help people be sure that the supplement contains what it says on the label, with no extra ingredients or impurities. The rules still don’t require that those who make or sell the product offer any proof that the herb or supplement is safe or effective, and they do not address the supplements’ effects on the body. They only address purity and manufacturing practices.
Still, a 2013 study done on herbal supplements in the US and Canada found that up to half of them didn’t contain what was on the label. More than half the tested samples contained contaminants or substances that were not listed on the label. Since the 2010 rules went into effect, many supplements have been recalled due to impurities or extra ingredients that were not listed on the label.
Because there’s growing interest in supplements, researchers have started studying some of them using the same methods used for cancer treatments and mainstream cancer prevention methods. Large sums of money are not usually available to study herbs and vitamins, so these studies tend to be smaller. But because the safety of the substance isn’t usually called into question, there’s less need for safety testing. When looking at studies of these herbs or supplements in people, look at the same questions as you would for cancer prevention clinical trials.
On the Internet, in conferences, and in health food stores, those who sell herbs will sometimes try to use lab studies or animal studies showing that the substance blocks cancer cells as evidence that the herbs work. Some sellers will refer to studies that are not published in peer-reviewed journals. The studies may be written up in a “natural cures” book or posted on a website. These can leave you with no way to know that the studies were done as they are presented.
It also happens that science researchers will isolate a chemical from an herb and test it in the lab to find out if it affects cells. But the effects of the isolated chemical might be very different from the effects of the whole herb (especially in large doses). This is why researchers may have to prove that the extract is safe before testing it in humans. This type of study is usually published in scientific literature and can be found there.
There’s a down side to tests of specific herbal extracts. If sellers of an herb know about scientific studies done with herbal extracts, some of them may talk about the study’s findings as if the study’s success means the whole herb works the same way. Purified extracts are just one part of the herb and may have different effects from the whole herb, and these 2 types of studies cannot stand in for one another.
Last Medical Review: 10/09/2014
Last Revised: 11/21/2014