Much of the information we have about the effects of vitamins comes from clinical trials. A clinical trial is an experiment conducted with patients as subjects. The strongest experimental design is the randomized design in which subjects (patients) are randomly assigned to treatment groups. Some clinical trials compare treatment methods and others assess the affect of a particular treatment on prevention of disease.
A controlled trial is a study in which researchers actively produce a treatment and deliberately assign people to the treatments.
In a randomized clinical trial, there are two or more therapeutic treatment groups. One treatment may be a placebo control in which a biologically inert substance is used. Often, the ‘control’ condition is compared to experimental treatments.
A trial in which the treatment is given in such a way that the subject cannot tell what it is. This helps to minimize other effects of the treatment, such as the placebo effect.
A double-blind trial is a completely random design where there is one real treatment and a placebo. Not only are the subjects assigned to the two groups at random, but neither the subjects nor those administering the treatments knows which treatment a subject is getting.
Researchers observe what happens but do not actively intervene with the assignment of people to treatment groups.
A trial in which participants receive two or more treatments one after the other and act as their own controls for comparison of drug treatments.
Evidence based upon haphazard observations which come to attention because they are striking in some way.
A factor that is not taken into account that gets mixed up with the treatment factors and has a marked effect on the response.
The favoring of certain outcomes not due to the treatments.
The study of the occurrence, distribution and causes of disease in man.
Prospective cohort study
In this type of epidemiological study two groups (cohorts) of subjects are identified, one of which is exposed to a treatment, an environmental condition, or health risk factor, and the other group is not. The subjects are then followed over time and the effects assessed.
In an epidemiological case-control study a group of patients who already have a disease or other outcome (the cases) is compared to another group of controls who do not. These studies are done retrospectively.
A systematic review of studies that pools the results of two or more studies to obtain the answer to an overall question of interest.
How reliable are scientific studies reported in the news?
Media reporting of nutritional issues can often add to the confusion that most people feel. Sometimes news stories about health seem to contradict one another, one says something is good for you, and another says that the same thing is bad for you. Conflicting medical reports can make even the most educated consumer confused about what to believe and what to do.
Nutrition stories regularly make headlines in newspapers and magazines and often seem credible because they claim to report ‘scientific research.’ Due to the pressure to report whatever is new, some stories get more media attention than they deserve and can become distorted in the process. News stories, particularly those on TV and radio, must often be condensed because of space limitations. It is worth analyzing the whole article to find out more about the research. Studies tend to carry more weight if they are done in large academic institutions, by well-qualified researchers and reported in reputable scientific journals which have been reviewed by other scientists. Studies done on humans rather than animals and on large groups of people are also more significant.
No single scientific study, however well done, can change the totality of evidence. There are many links in the process of drawing conclusions about the course of a disease and the ability of vitamins and minerals to affect it. A new study may move current thinking a little bit more in one direction than another, but a large number of studies from different places are necessary to understand a disease process. Science requires repeatable experiments. If a nutrient is useful, the effects will be seen time and again if the experiments are done properly.