The essential metals for humans: a brief overview

doi:10.1016/j.jinorgbio.2019.03.013

Journal of Inorganic Biochemistry

Volume 195, June 2019, Pages 120-129

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Highlights

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Essential elements for life
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Essential metal ions for human body
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Bulk and trace essential metal ions
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Metals for life and hard and soft chemical character

Abstract

The human body needs about 20 essential elements in order to function properly and among them, for certain, 10 are metal elements, though for every metal we do need, there is another one in our body we could do without it. Until about 1950 poor attention was given to the so-called “inorganic elements” and while researches on “organic elements” (C, N, O and H) and organic compounds were given high priority, studies on essential inorganic elements were left aside.

Base on current knowledge it is ascertained today that metals such as Na, K, Mg, Ca, Fe, Mn, Co, Cu, Zn and Mo are essential elements for life and our body must have appropriate amounts of them.

Here a brief overview to highlight their importance and current knowledge about their essentiality.

Graphical abstract

The human body needs about 20 essential elements in order to function properly and among them, for certain, 10 are metal elements, such as Na, K, Mg, Ca, Fe, Mn, Co, Cu, Zn, Mo.

Here a brief overview to highlight their importance and current knowledge about their essentiality.

Introduction

Although it is continuously discussed which elements should be classified as toxic, beneficial or essential for living organisms especially for humans, around 20 of the known elements are defined as essential today, though the precise requirements can differ within different organisms (Fig. 1).

First, there are the “organic” and “bulk” elements H, C, N, and O. In addition seven “macro-minerals” are essential, namely Na, K, Mg, Ca, Cl, P, and S.

Furthermore, “trace elements” are defined as essential, namely Mn, Fe, Cu, Zn, Se, Co, Mo and I for plants or animals. At present, some other elements are under discussion to be included in the category as essential for both, such as for example V, Ni, Br, Si, Sn [[1], [2], [3], [4]].

For As, but also for Pb a positive effect of traces has been discussed for certain organisms, indicating the uncertainties in classification of many trace elements [5].

In fact, a dose-response diagram (Fig. 2) shows that also essential elements for human life can be toxic if the dose is high enough, pointing to the Paracelsus principle “the dose makes the poison”.

Possibly, during the evolution of life, a biological function could be developed for all natural occurring elements. It is noteworthy that elements such as silicon or aluminium that are so abundant in the earth's crust play only marginal roles in the biological systems and this has been related to the water insolubility of their compounds, oxide or hydroxide, at physiological pH. On the other hand, a rare element such as for example molybdenum is quite soluble as MoO₄²⁻ oxyanion at physiological pH and it has been found to be essential in many living organisms [6].

Section snippets

Essential metal elements

Which elements are essential or beneficial and which are nonessential and only toxic for a certain organism is still under discussion, particularly for humans [7].

Despite the complexity of their functions, some characteristic deficiency symptoms of metal elements for humans are quite familiar and are reported in Table 1 [8].

As far as the toxicity is concerned, two groups can be distinguished: those for which the low abundance or the low bioavailability make them not necessary for life, and

Biological relevance of essential metal elements

Metal elements can be taken up, accumulated, transported or stored depending on their function and activities.

Though there is a long pathway to be undertaken before our understanding of the complex biological chemistry of life, some of the most important biological functions of essential metal elements are summarized here [2,3,23].

Toxic effects of essential and non-essential elements

Both essential and nonessential metals may exert toxic effects if the dose of ingestion or exposure exceeds certain levels [96], often referred to as critical levels. The effects induced at these levels by a toxic agent may be referred to as critical effects. These effects arises from the so-called critical organ [97]. For example, the central nervous system is the critical organ in cases of elemental mercury vapor exposure. When discussing metal toxicity it should be emphasized that not only

Conclusions

Here we have briefly reviewed metals which are today considered essential for human life, with no intention to present a comprehensive review, but rather an attempt to highlight current general knowledge about essential metal elements.

According to current knowledge, 60 of the elements in the Periodic Table are elements contained in human body but only about 20 of these are considered to be essential for life, no matter what type of organism is under debate, and to take part in the healthy

Acknowledgements

VMN and MAZ acknowledge the financial support by MIUR-PRIN 2015 – 2015MP34H3.

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Review Article The essential metals for humans: a brief overview

Highlights

Abstract

Graphical abstract

Introduction

Section snippets

Essential metal elements

Biological relevance of essential metal elements

Toxic effects of essential and non-essential elements

Conclusions

Acknowledgements

J. Nutr.

J. Trace Elem. Med. Biol.

Best Pract Res Clin Endocrinol Metab

J. Biol. Chem.

Am. J. Clin. Nutr.

Curr. Opin. Chem. Biol.

Biomed. Pharmacother.

Adv. Nutr.

J. Inorg. Biochem.

Adv. Nutr.

J. Inorg. Biochem.

Int. Rev. Neurobiol.

J. Trace Elem. Med. Biol.

NeuroToxicology

Am. J. Hum. Genet.

J. Trace Elem. Med. Biol.

Toxicol. Appl. Pharmacol.

Clin. Chim. Acta

Adv. Nutr.

Medicine

Biochimie

Regul. Toxicol. Pharmacol.

The chemical elements of life

J. Chem. Soc. Dalton Trans.

The Biological Chemistry of the Elements: The Inorganic Chemistry of Life

The essential trace elements

Science

Nutritional requirements for boron, silicon, vanadium, nickel, and arsenic: current knowledge and speculation

FASEB J.

The Elements. Their Origin, Abundance, and Distribution

The metals in the biological periodic system of the elements: concepts and conjectures

Int. J. Mol. Sci.

Interrelations between Essential Metal Ions and Human Diseases

Heavy metals and human health: mechanistic insight into toxicity and counter defense system of antioxidants

Int. J. Mol. Sci.

Is the major part of the periodic system really inessential for life?

J. Trace Elem. Electrolytes Health Dis.

Chromium is not an essential trace element for mammals: effects of a “low-chromium” diet

JBIC Journal of Biological Inorganic Chemistry

Is chromium a trace essential metal?

BioFactors

Oral chromium exposure and toxicity

Curr Environ Health Rep

Effect of strontium ranelate on bone mineral density in men with osteoporosis

Actualizaciones en Osteología

Potential mechanisms of action of lithium in bipolar disorder. Current understanding

CNS Drugs

Therapeutic potential of mood stabilizers lithium and valproic acid: beyond bipolar disorder

Pharmacol. Rev.

Lithium in the prevention of suicide in mood disorders: updated systematic review and meta-analysis

BMJ

Hard and Soft Acids and Bases

The Inorganic Chemistry of Biological Processes

Hard and soft acids and bases

J. Am. Chem. Soc.

The role of essential metal ions in the human organism and their oral supplementation to the human body in deficiency states

Orv. Hetil.

Nature's Building Blocks: An AZ Guide to the Elements

Crystal structure of the calcium pump of sarcoplasmic reticulum at 2.6 A resolution

Nature

The plasma membrane calcium pump in health and disease

FEBS J.

Hypercalcemia of malignancy and new treatment options

Ther. Clin. Risk Manag.

Hypercalcemia of malignancy: an update on pathogenesis and management

N. Am. J. Med. Sci.

Review Article
The essential metals for humans: a brief overview