Experimental Epidemiology Studies

Experimental (laboratory) studies involve more than observing and gathering data. Scientists make small, defined changes in one or more sets of the test subjects - cells, tissues, animals or people. Then they compare the various outcomes. These studies can be done in two basic ways: in vitro (test tubes) and in vivo (living organisms-mice or people)

In Vitro

In vitro studies are experiments performed in test tubes. These studies help researchers figure out for instance precisely how and why certain foods or food substances might protect against cancer.

Seeking clues as to the complicated array of chain reactions that happen after we consume a particular nutrient, researchers examine animal or human cells or tissues removed from the body.

For example, an epidemiological study can suggest that eating green beans protects against cancer. But that's only an association. Using in vitro studies, scientists can look at the chain of events that happens when nutrients and cancer cells meet.

Put those two types of studies together, and you're closer to solving the mystery than with either type of study alone.

Advantages:

In vitro studies are tightly structured, which means that scientists can control for many confounding variables. Once an in vitro study finds a "suspect" - a biological mechanism that might protect against or add to your risk of cancer - researchers can then test their hypotheses in an animal model.

Disadvantages:

In vitro studies can't tell us if an anti-cancer effect that happens at the cell level also occurs in the "real world" of the complex human body. In vitro does not mimic physiological conditions of a living organism like a mouse model or human.

		They also can't tell us how much we might have to eat of any substance to reap anti-cancer benefits, and they can only involve food components, not whole foods, since one can't feed a cell an apple. Image courtesy of American Institute of Cancer Research

In Vivo

In vivo studies can put hypothesis to the test in complex living organisms. If cell or tissue studies (in vitro) provide evidence that intervention X protects against cancer, an in vivo study can give researchers the next clue.

Advantages:

Testing interventions in animal models allows scientists much stricter control than with humans. Unless they lock you in the lab, you're probably going to eat those Oreos, but a mouse eats what he's fed - so researchers know exactly what's going in and what's going out.

Disadvantages:

Humans aren't mice. While the fast majority of our biological processes are similar - especially the cancer process - many things that happen in mice don't happen the same way in humans, and vice versa.

		Image courtesy of American Institute of Cancer Research

Clinical Trials - The next step

If an animal experiment is successful, usually the next usual formal epidemiological experiment is a randomized controlled clinical trial, conducted to test a preventive or therapeutic regimen or diagnostic procedure. In controlled trials, scientists don't just observe what happens to study subjects as they live their lives. Rather, they make specific changes to their lives to see how those changes affect them.

Chart courtesy of the National Cancer Institute (NCI)

One group of study participants, the "intervention group", consumes foods or nutrients scientists think may protect against cancer. Other participants, the "control group," get a different "food prescription" - often just a placebo.

Advantages:

Controlled trials avoid many of the types of bias that can be found in other studies. They also let scientists keep tight control over the enormous complexity of our daily lives.

		Disadvantages: Controlled trials are often called the scientific "gold standard." This can be true in many situations, but for unraveling the mystery of linkages between diet and cancer prevention, this investigation method may not be perfect. It's hard to "blind" people to dietary modifications because you know what you're eating, and you'll be aware if someone changes it. Image courtesy of American Institute of Cancer Research

That's why many controlled trials involving diet and cancer give the nutrients in the form of a supplement. One group gets the supplement being tsted and the conrol group get a "placebo".

It's important to remember that even if scientists show that an isolated supplement produces no anti-cancer effects, this won't tell us anything conclusive about how whole foods or diets made up of many different foods affect cancer risk.

And since cancer can take decades to develop, it's hard to know if a study has lasted long enough to influence cancer development and/or prevention. Nevertheless, a positive result from a controlled trial can provide strong evidence that a particular nutrient has a protective effect against cancer so further testing or observational studies can be undertaken.