Randomized Controlled Trial (RCT)

clinical trial with at least one active treatment group (e.g., taking a vitamin) and a control (e.g., placebo) group. In RCTs, participants are chosen for the experimental and control groups (e.g., placebo-controlled) at random, and are not told whether they are receiving the active or placebo treatment until the end of the study. A RCT in which neither the investigators administering the treatment nor the participants know which participants are receiving the experimental treatment and which are receiving the placebo is called “double blind”. RCTs are always prospective studies.
RCTs, the gold standard for drug testing, are considered to be of high quality because the risk of bias is minimized. An RCT can provide evidence and can establish cause-and-effect relationships (hypothesis-testing).

RCT cannot readily be applied to nutrients as it is not possible to compare the effect of micronutrient-intake with a control group without any dietary exposure. So far, no good metrics or measures (i.e., for micronutrient efficacy) to establish a baseline for comparisons (i.e. effect with vs. without micronutrient) are available.

Randomized design

An experiment in which participants are chosen for the experimental (e.g., exposure to a micronutrient) and control (e.g., placebo-controlled) groups at random, in order to reduce bias caused by self-selection into the groups.

Recommended Daily Allowances or Recommended Dietary Allowances (RDA)

The daily dietary intake level of a nutrient considered sufficient to meet the requirements of nearly all (97–98%) healthy individuals in each life stage and gender group.

Redox reaction

A redox reaction ─ another term for an oxidation-reduction reaction ─ is any reaction in which electrons are removed from one molecule or atom and transferred to another molecule or atom. In such a reaction one substance is oxidized (loses electrons) while the other is reduced (gains electrons).


A chemical reaction in which a molecule or atom gains electrons. The reducing agent (reductant) transfers electrons to another substance, and is thus, ─ as “electron donor ─ oxidized itself.


The nerve layer that lines the back of the eye. In the retina, images created by light are converted to nerve impulses, which are transmitted to the brain via the optic nerve.

Retrospective study

A study that looks backwards and examines exposures to suspected risk or protection factors in relation to an outcome that is already established before the study commences. Retrospective studies rely on data (e.g., about nutritional behavior and developed diseases) that have already been collected in the past or need to be recalled by the participants. Case-control studies are usually retrospective, cohort studies sometimes are, randomized controlled trials never are.

Retrospective studies are considered to be of comparable poor quality as the risk of bias (e.g., inaccurate recollection of past behavior) is high. Sources of bias are more common in retrospective studies than in prospective studies.


A review article in the medical literature summarizes a number of different studies and may draw conclusions about a particular intervention. Review articles are often not systematic.


A softening of bones in children potentially leading to fractures and deformity. Rickets is among the most common childhood diseases in many developing countries. The predominant cause is a vitamin D deficiency, but lack of adequate calcium may also lead to rickets.