General information on zinc

Zinc is a micronutrient or mineral that belongs to the category of trace elements. It is present in small quantities in the body, in trace amounts. After iron, zinc is the most abundant trace element in the body: about 2 to 3 g. In biology, zinc is generally found as the divalent cation Zn²⁺.

Zinc is essential for many functions and systems in the body. It is involved in the activity of more than 300 enzymes and more than 1000 transcription factors (regulation of gene expression). It contributes to the normal functioning of the immune system, the skin repair mechanisms and the thyroid gland. In summary, it can be described as :

• A structural component,
• A catalytic factor,
• A signaling mediator.

The discovery that zinc is essential for animal growth dates back to the 1960s, when the consequences of a deficiency were, however, unknown to the clinical world. The first recommendations for zinc intake were made in 1974, following the demonstration of the therapeutic effects of zinc [1]

In our diet, zinc is found mainly in seafood (fish and shellfish) and meat (including offal), followed by cheese and legumes. Although our overall zinc intake is sufficient, our dietary habits and the specifics of our diet are determining factors in our zinc status (e.g., reduction or withdrawal of animal products).

Zinc for health [2,3]

Zinc is essential for basic cellular functions such as growth, differentiation and survival. This gives it a major global role in our health:

• Metabolic functions,
• Cellular development,
• Reproductive system,
• Cellular defense,
• Neuronal function,
• Protein synthesis
• Immune system,
• Thyroid function,
• Wound healing, 
• Smell and taste,
• and blood coagulation.

Specifically, it is involved in oxidative stress response, immune response, DNA replication, DNA damage repair and cell cycle progression. Zinc is essential for protein and collagen synthesis, thus contributing to skin health.
A review published in early 2022 provides a recent overview of the link between zinc and health [4]. To date, zinc intakes have been well documented during pregnancy, growth and metabolism in general. It is in the latter context that zinc supplementation is associated with a reduced risk of certain metabolic disturbances.
Worldwide, the prevalence of zinc deficiency is estimated to be 17% [5]. 5] Within this average, it is more prevalent in developing countries. Zinc deficiency generally leads to multi-organ disease, including impaired immunity and increased susceptibility to infection. It is important to note that there is no need for excessive daily zinc supplementation, especially since high intakes can lead to digestive disorders [6].

Our zinc needs

Many dietary factors can affect the bioavailability of the zinc we ingest. Among them, phytates, molecules present in plant sources (cereals, legumes, oilseeds) that reduce its absorption. This element must therefore be taken into account. The nutritional guidelines for zinc have been adapted according to the level of phytates in the diet to ensure that they are sufficient (see table below) [7]. 

*Phytates are supplied by the diet via phosphorus
**Recommended intakes defined by the EFS

With regard to these nutritional benchmarks, several observations can be made:

• The needs are more important in adult men,
• Needs increase during the perinatal period and while breastfeeding,
• The needs are to be adjusted according to the consumption of phytates (of vegetable origin), and whatever the source of zinc, animal or vegetable, the presence of phytates always limits the absorption of food zinc.

Zinc metabolism

Zinc (whether contained in our food or in the form of zinc supplements) is primarily absorbed in the distal duodenum and proximal jejunum of the small intestine, just after the stomach and before the intestine.
Only 0.1% of zinc is found in serum (blood). This trace element is mainly stored in :

• skeletal muscle (about 60%) 
• bones (about 30%)
• skin and liver (about 5% respectively).

More widely, it is distributed throughout the body, including the brain, lungs and kidneys, in smaller quantities (<1%) [8,9]. This storage cannot be mobilized by the body to meet its needs, which emphasizes that our daily diet plays a key role in our zinc intake.
Zinc homeostasis in the body is ensured by specific zinc transporters (ZIP transporters for entry of zinc into the cell or organelle, and ZnT for exit of zinc from the cell or organelle) and metallothioneins (transport proteins). The purpose of this regulation is to maintain the intracellular zinc levels necessary for cell function.

At the intestinal level, zinc absorption is also ensured by transporters. The overall balance is between exogenous (dietary) intake, reabsorption (endogenous) and excretion through urine or faeces. To a lesser extent, sweat and skin peeling also contribute to zinc balance.

The bioavailability of zinc [8,10,11]

The diet provides different sources of zinc according to different food matrices (structure and composition of the food). As mentioned above, zinc absorption is subject to dietary factors that can limit it, such as phytates. Phytates are the primary factor inhibiting zinc absorption. Conversely, dietary protein intake increases the bioavailability of zinc, especially animal protein.
Other factors are involved in the bioavailability of zinc and are particularly important when choosing a good zinc food supplement:
1/ The solubility of the form of zinc: while the individual's zinc status is not necessarily a factor to be taken into account, the absorption of zinc is on the other hand largely determined by its solubility at the intestinal level. And this solubility is itself dependent on the chemical form of zinc and the presence of specific inhibitors or enhancers of zinc absorption.
2/ The amount of intake: the lower the intake, the greater the absorption. It has been reported that the absorption rate of zinc is on average 33%. For insoluble minerals such as zinc, binding to carriers or chelators has a positive effect on both their solubility and dispersion, and thus their absorption.

The zinc of Nutri&Co 

When it comes to minerals, assimilation and tolerance are the criteria to look for.
Zinc is generally found in the form of zinc salts: zinc gluconate, zinc acetate, zinc sulfate, zinc picolinate, zinc orotate, zinc citrate... A clinical study published in 2014 showed that, among these salts, the picolinate and gluconate forms have better bioavailability (about 60%) compared to zinc oxide (about 50%).

For our Zinc formula dedicated to immunity and fertility, we have specially combined 2 forms of zinc for their high bioavailability:

• A zinc gluconate: this is a highly bioavailable and soluble form of zinc thanks to its association with gluconate. It delivers 14.4% of zinc-element. The gluconate allowing its optimal bioavailability is of vegetable origin, certified without GMO nor pesticides. 
• A liposome zinc oxide: the encapsulation of the zinc oxide by fatty acids allows to reduce the interactions of zinc with the surrounding factors limiting its absorption. 

In a single capsule, these two forms provide 10 mg of elemental zinc, i.e. 100% of the reference intake, while guaranteeing good digestive tolerance.

To this highly assimilated zinc duo, we have associated a highly bioavailable selenium yeast for a reinforced action on the immune system and the cognitive sphere [12,13].Selenium deficiency promotes a decrease in the proliferation of immune cells (T and B lymphocytes) and affects the immune system via a decrease in antibodies (immunoglobulins). Selenium also participates in the antioxidant response by entering the formation of selenoproteins. In summary, selenium strongly influences the anti-inflammatory and immune response [14]. A selenium intake is therefore interesting as a complement to our zinc duo.

References

1. Prasad, A.S. Discovery of Human Zinc Deficiency: Its Impact on Human Health and Disease. Adv. Nutr. 2013, 4, 176–190, doi:10.3945/an.112.003210.
   
2. Prasad, A.S. Zinc in Human Health: An Update. J. Trace Elem. Exp. Med. 1998, 25.
3. Chasapis, C.T.; Ntoupa, P.-S.A.; Spiliopoulou, C.A.; Stefanidou, M.E. Recent Aspects of the Effects of Zinc on Human Health. Arch. Toxicol. 2020, 94, 1443–1460, doi:10.1007/s00204-020-02702-9.
4. Li, J.; Cao, D.; Huang, Y.; Chen, B.; Chen, Z.; Wang, R.; Dong, Q.; Wei, Q.; Liu, L. Zinc Intakes and Health Outcomes: An Umbrella Review. Front. Nutr. 2022, 9, 798078, doi:10.3389/fnut.2022.798078.
5. Wessells, K.R.; Brown, K.H. Estimating the Global Prevalence of Zinc Deficiency: Results Based on Zinc Availability in National Food Supplies and the Prevalence of Stunting. PLoS ONE 2012, 7, e50568, doi:10.1371/journal.pone.0050568.
6. Rabinovich, D.; Smadi, Y. Zinc; Treasure Island.; StatPearls Publishing, 2022;
7. ANSES Actualisation Des Repères Du PNNS : Élaboration Des Références Nutritionnelles; 2016; p. 196;.
8. Kambe, T.; Tsuji, T.; Hashimoto, A.; Itsumura, N. The Physiological, Biochemical, and Molecular Roles of Zinc Transporters in Zinc Homeostasis and Metabolism. Physiol. Rev. 2015, 95, 749–784, doi:10.1152/physrev.00035.2014.
9. Maares, M.; Haase, H. A Guide to Human Zinc Absorption: General Overview and Recent Advances of In Vitro Intestinal Models. Nutrients 2020, 12, 762, doi:10.3390/nu12030762.
10. Hambidge, M.; Krebs, N.F. Zinc Metabolism and Requirements. Food Nutr. Bull. 2001, 22, 126–132, doi:10.1177/156482650102200202.
11. Roohani, N.; Hurrell, R.; Kelishadi, R.; Schulin, R. Zinc and Its Importance for Human Health: An Integrative Review. J. Res. Med. Sci. 2013, 14.
12. Warthon-Medina, M.; Moran, V.H.; Stammers, A.-L.; Dillon, S.; Qualter, P.; Nissensohn, M.; Serra-Majem, L.; Lowe, N.M. Zinc Intake, Status and Indices of Cognitive Function in Adults and Children: A Systematic Review and Meta-Analysis. Eur. J. Clin. Nutr. 2015, 69, 649–661, doi:10.1038/ejcn.2015.60.
13. Wessels, I.; Maywald, M.; Rink, L. Zinc as a Gatekeeper of Immune Function. Nutrients 2017, 9, 1286, doi:10.3390/nu9121286.
14. Hoffmann, P.R.; Berry, M.J. The Influence of Selenium on Immune Responses. Mol. Nutr. Food Res. 2008, 52, 1273–1280, doi:10.1002/mnfr.200700330.
15. Prasad, A.S.; Mantzoros, C.S.; Beck, F.W.J.; Hess, J.W.; Brewer, G.J. Zinc Status and Serum Testosterone Levels of Healthy Adults. Nutrition 1996, 12, 344–348.