Guide: Zinc, Iron
& Cognitive Function

Chapter 1: The Basics of Cognitive Function

The term cognitive function describes all the mental processes that allow people to take in, process and store information and to plan actions based on it. These processes take place in the central nervous system and rely on a complex interplay of nerve cells, synapses and neurotransmitters.

1.1 The neural architecture

The human brain contains an estimated 86 billion neurons that communicate with each other through trillions of synaptic connections. Every cognitive task — from simply recognizing a face to solving abstract math problems — relies on the coordinated activity of specific neural networks.

Signals are passed on at the synapses by chemical messengers (neurotransmitters), whose synthesis, release and reuptake depend on numerous enzymatic processes. Minerals act as cofactors for many of these enzymes and are therefore involved in the biochemical basis of cognitive processes.

1.2 What areas does cognitive function include?

Cognitive function can be divided into several sub-areas, each engaging different brain regions:

1. Perception: Processing of sensory input from the eyes, ears, skin and other sense organs in the sensory cortex.
2. Attention: Targeted focus on relevant stimuli, controlled by the prefrontal cortex and the attention network.
3. Memory: Encoding, consolidating and retrieving information, with the hippocampus playing a special role.
4. Language: Producing and understanding language in Broca's and Wernicke's areas.
5. Executive control: Planning, decision-making and impulse control in the prefrontal cortex.

1.3 The role of minerals

For the processes described above to function properly, the brain needs a continuous supply of oxygen, glucose and certain micronutrients. Two minerals — zinc and iron — have an EU-authorized health claim relating to normal cognitive function.

Chapter 2: Zinc and Cognitive Function

2.1 Zinc in the nervous system

Zinc is a divalent cation (Zn²⁺) found in particularly high concentrations in the brain. Certain neurons — known as zincergic neurons — store zinc ions in synaptic vesicles and release them during signal transmission. This process has been observed especially in the hippocampus, the amygdala complex and parts of the neocortex.

At the synapses, released zinc modulates the activity of various receptors, including NMDA receptors and GABA receptors. These receptors are involved in synaptic plasticity — a mechanism considered the biochemical basis of learning and memory processes.

2.2 Zinc finger proteins and gene expression

Another link between zinc and cognitive function is zinc finger proteins. These transcription factors need zinc ions for their three-dimensional structure and bind to specific DNA segments to control the expression of certain genes. In the nervous system, zinc finger proteins control, among other things, the expression of genes coding for growth factors, receptor proteins and enzymes of neurotransmitter synthesis.

2.3 Daily requirement and food sources

According to EU Regulation 1169/2011, the reference value for daily zinc intake is 10 mg. Different foods provide different amounts of zinc:

2.4 Bioavailability

The absorption of zinc in the small intestine is subject to various factors. Phytic acid, which occurs naturally in grains and legumes, can bind zinc and reduce its absorption. Preparation methods such as fermenting, sprouting and soaking can reduce phytic acid content. At the same time, the presence of certain amino acids (such as histidine and cysteine) favors zinc absorption.

Chapter 3: Iron and Cognitive Function

3.1 Iron and oxygen transport to the brain

As a central component of hemoglobin, iron is responsible for transporting oxygen in the blood. Since the brain, despite its comparatively low weight (about 2 % of body weight), accounts for around 20 % of total oxygen consumption, a reliable oxygen supply to neurons is of particular importance for cognitive processes.

In addition, the brain contains myoglobin-like proteins (neuroglobin), which also contain iron and are involved in local oxygen buffering in nerve cells.

3.2 Iron and neurotransmitter synthesis

As a cofactor of several enzymes, iron is involved in the biosynthesis of neurotransmitters:

• Tyrosine hydroxylase: This iron-dependent enzyme catalyzes the rate-limiting step in the synthesis of dopamine and norepinephrine — two neurotransmitters involved in motivation, attention and reward processing.
• Tryptophan hydroxylase: Another iron-dependent enzyme, required for the synthesis of serotonin from the amino acid tryptophan. Serotonin influences mood and cognitive flexibility, among other things.
• Myelination: Iron is involved in the formation and maintenance of the myelin sheaths that surround nerve fibers and determine the speed of signal transmission.

3.3 Daily requirement and food sources

The EU reference value for iron is 14 mg per day. A distinction is made between heme iron (from animal sources, higher bioavailability) and non-heme iron (from plant sources):

3.4 Absorption and bioavailability

Iron is absorbed mainly in the duodenum. Heme iron is taken up via its own transport mechanism and has an absorption rate of 15–35 %. Non-heme iron is absorbed via the DMT1 transporter; its uptake can be enhanced by vitamin C and inhibited by phytates, polyphenols and calcium.

Chapter 4: Similarities and Differences

Zinc and iron each contribute to normal cognitive function according to their own EU-authorized claims. However, their mechanisms of action are fundamentally different:

Note that each health claim refers to the individual mineral:

4.1 Practical dietary notes

A balanced diet can provide both zinc and iron in sufficient amounts. Foods such as beef, legumes and rolled oats contain both minerals. On a plant-based diet, it is recommended to combine iron-rich foods with sources of vitamin C to favor non-heme iron absorption, and to soak legumes to reduce phytic acid, which can reduce both zinc and iron absorption.

When using dietary supplements, the recommended daily intake should not be exceeded. Dietary supplements are not a substitute for a varied diet.

Chapter 5: Frequently Asked Questions

What does “normal cognitive function” mean?

The word “normal” in the EFSA claims refers to physiologically proper function when there is an adequate supply of the mineral in question. It describes neither a therapeutic effect nor any increase in performance beyond the regular level.

How can you find out your own mineral status?

Zinc status is usually determined via the serum zinc level. For iron, in addition to serum iron, ferritin (stored iron), transferrin saturation and a blood count (hemoglobin level) are often used. Testing is done by a physician.

Can zinc and iron be taken at the same time?

Some studies suggest that high doses of one mineral can affect the absorption of the other in the gut. At doses matching the daily reference values, this is usually not a problem. If in doubt, it is advisable to consult a medical professional.

Which groups of people should pay particular attention to their intake?

The authorized claims refer to the general adult population. Certain groups — such as pregnant women, breastfeeding women, vegetarians and vegans, and older adults — may have increased needs or reduced absorption. Individual advice from a medical professional is recommended.

What other EFSA claims exist for zinc and iron?

Both zinc and iron have further authorized health claims under Regulation (EU) No 432/2012 that relate to other functions (e.g. the immune system, cell division, energy metabolism). This guide focuses exclusively on the claims about normal cognitive function.