Nutrition Research Studies: Types and Examples

Purpose

The purpose of nutrition research studies is to find beneficial and harmful effects of nutrients in humans. Below are the study types listed from least to most reliable (probably…). All examples are about the effect of vitamin C therapy on cancer.

Laboratory or “In Vitro” Studies

The studies of nutrients effects often start in the laboratories. They are called “in vitro” or, literally “in glass” studies, as opposed to “in vivo” or “in the live human body” studies.

• An example: Cytotoxic effect of ascorbate [vitamin C] and its derivatives on cultured malignant and nonmalignant cell lines. The study conclusion: The results support the hypothesis that the cytotoxic activity of ascorbate was due to its chemical properties and that certain oxidation and degradation products of ascorbate were cytotoxic agents ^[4].

Animal Studies

Animal trials are often performed before human trials.

• An example: Pharmacologic concentrations of ascorbate are achieved by parenteral administration and exhibit antitumoral effects. Finding: Parenteral administration of ascorbate decreased the growth rate of a murine hepatoma [liver cancer], whereas oral administration of the same dosage did not ^[5].

Case Reports

A case report is an anecdotal report of an effect or side effect of a particular nutrient in one or more human individuals. Case reports are not studies, so they have to be interpreted carefully.

• An example: Reticulum cell sarcoma: double complete regression induced by high-dose ascorbic acid [vitamin C] therapy. Report: At the time of first diagnosis, the disease was widely disseminated, and a very dramatic regression of all parameters of disease activity was induced by the continuous administration of large doses of ascorbic acid [vitamin C] ^[11].

Observational Studies

In observational studies, researchers observe a group of individuals and compare their nutrients intake with diseases they have or develop during the study period. An observational study may include interviews, estimation of the nutrient content of foods and checking of personal medical documentation but no “intervention,” that is no instructions what to eat and no treatment.

Case Control or Retrospective Studies

In a case control study, researchers choose a group of “cases,” that is individuals with a certain disease and look back into their medical documentation. Then they check how a certain nutrient therapy was associated with the disease development and compare results with a control group of individuals with the same disease who were not treated with that nutrient.

• An example: Dietary antioxidants and lung cancer risk. The study findings: With the exception of lycopene and vitamin C, the remaining antioxidants were associated with significant reductions in risk of lung cancer ^[6].

Prospective Cohort Studies

A cohort is a group of the study participants with similar characteristics, like the same sex or race or geographical area, certain age, etc. In a prospective cohort study, researchers choose a group of individuals and follow them forward for a certain period and then check if an intake of certain nutrients was associated with certain diseases.

• An example: Intake of …vitamin C…and prostate cancer risk. Finding: For intake of…vitamin C…no effect on overall prostate cancer risk was found ^[3].

Interventional Studies (Experiments, Trials)

In interventional studies, researchers instruct participants what to eat or they provide them with dietary supplements and then observe the health effects through a certain period.

Controlled Clinical Trials (CTT)

In a controlled clinical trial, one or more groups of participants receives certain nutrients, but a control group does not receive any nutrient, or receives a placebo–an inactive substance, which appears just like a real nutrient–in this case the trial is called placebo-controlled. The term double-blinded means that neither the participants nor the researchers who collect the data during the study know, who gets the real nutrients and who a placebo.

Randomized Controlled Trials (RCT)

Randomized controlled trial are clinical trials in which participants are assigned to either treatment or controlled groups randomly and not on the basis of their individual characteristics. Usually, a computer program is used to randomize participants into groups.

• An example: High-dose vitamin C versus placebo in the treatment of patients with advanced cancer who have had no prior chemotherapy. Conclusion: High-dose [oral ] vitamin C therapy is not effective against advanced malignant disease regardless of whether the patient has had any prior chemotherapy ^[7].

Literature Reviews

In a literature review, researchers read several articles on a certain topic published in the medical literature and express their opinions about the effects of nutrients in question.

• An example: Vitamin C. Conclusion: Overall, observational prospective cohort studies report no or modest inverse associations between vitamin C intake and the risk of developing a given type of cancer ^[9].

Meta Analysis

In a meta analysis, researchers gather data from large number of various types of studies and present results as if it were one study. A meta analysis is a quantitative view, which means results are not evaluated by researchers but mathematically calculated.

• An example:Vitamin C and survival among women with breast cancer. Conclusion: Dietary vitamin C intake [from foods and supplements] was statistically significantly associated with a reduced risk of breast cancer-specific mortality ^[8].

Systematic Reviews

In a systematic review, researchers perform a research of available studies about a certain nutrient-related topic, carefully select the quality trials–preferably randomized controlled trials–following a strict research methodology and provide conclusions about the effects of the studied nutrients. A systematic review is a qualitative view; it considers the context, such as the quality of studies, possible bias and applicability.

• An example: Effect of the supplemental use of antioxidants vitamin C…for the prevention and treatment of cancer. Conclusion: The systematic review of the literature does not support the hypothesis that the use of supplements of vitamin C…generally help prevent and/or treat cancer ^[10].