Zinc – a mineral essential for life

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Few minerals have as many different roles in our bodies as zinc (Zn). It is an essential mineral, which means we have to obtain it from food. It is also the second most abundant element in the body after iron. Recommended daily intakes of zinc vary, but according to EFSA, the reference intake for men should range from 9.4 to 16.3 mg/day, and for women from 7.5 to 12.7 mg/day. Excessive doses of zinc (more than 150 mg/day) can cause digestive problems, while prolonged intake of more than 60 mg of zinc per day may hinder the absorption of copper.

It is estimated that around 17% to 20% of the world’s population is at risk of zinc deficiency. The prevalence of zinc deficiency is highest in South Asia (30%) and Africa (26%), while in high-income countries it is estimated at 8%. Symptoms of zinc deficiency can include stunted growth, alopecia, diarrhoea, delayed sexual maturation, impotence, eye lesions, decreased appetite, and loss of sense of smell and taste. In adults, especially the elderly, zinc deficiency can cause slower healing of wounds and cognitive impairment. These problems may occur even when blood zinc concentrations are within the normal range, but nearer to the lower limit. Certain groups are at higher risk of zinc deficiency, including people who follow a predominantly plant-based diet, pregnant or breastfeeding women, older adults, people with gastrointestinal disorders or those who have undergone bariatric surgery, and people with alcohol use disorders.

Zinc is abundant in foods of animal origin, such as meat, oysters, liver, and eggs. It is absorbed from food in the digestive tract, entering the bloodstream and being transported by blood proteins to the tissues and organs that require it. In plant foods, it is found in beans, cereals and seeds, but is more difficult for the body to use due to the presence of phytates, which bind zinc and inhibit its absorption.

Because of its broad range of effects on our bodies, zinc is considered to be one of the most vitally important minerals. When it comes to the functions it performs in the body, it is probably best known for its antioxidant activity, which protects cells from oxidative damage. It is also important in treating wounds and maintaining skin health, as it aids healing and has anti-inflammatory properties. Zinc contributes to several physiological functions such as cell division, protein synthesis, and the synthesis of DNA and RNA. It is also responsible for the expression of various genes, since many transcription factors have zinc receptors. This is why zinc is considered essential for normal growth and development. Nevertheless, it should be stressed that zinc has a much broader impact on our bodies.

It supports the immune system by activating and producing T lymphocytes, which fight pathogens. It regulates the intracellular signalling pathways of innate and adaptive immune cells.

Zinc also plays an important role in supporting the endocrine system. In fact, it is essential for the formation and structural stability of insulin. This is why there is a higher concentration of zinc in the beta cells of the pancreas. Zinc ions act on the insulin signalling pathway, stimulating lipogenesis and glucose uptake in adipocytes. Zinc is also involved in the thyroid hormone metabolism, for example protein anabolism, as well as in increasing the basal metabolic rate and supporting bone growth in children. It regulates the synthesis of thyroid-stimulating hormone (TSH). Consequently, zinc deficiency leads to a drop in TSH, serum triiodothyronine (T3), and thyroxine (T4) levels in the body. Some studies indicate that chronic zinc deficiency may be the cause of subclinical hypothyroidism.

This mineral is also important for fertility, especially in men. Its mode of action could make it a significant factor in the prevention and treatment of male infertility.

High concentrations of zinc can be found in the human retina. Studies have shown a link between high intakes of antioxidants, including zinc, and a reduced risk of age-related macular degeneration (AMD), which is a major cause of vision loss. According to these studies, dietary supplementation with antioxidants such as zinc may help to slow the progression of AMD and prevent damage to retinal cells.

However, the effects of zinc on the nervous system are particularly important. It is essential for the normal development and function of the central nervous system. Zinc deficiency affects zinc homeostasis in the brain, resulting in changes in behaviour, learning, mental abilities, and increases the risk of epileptic seizures. Depression and anxiety are two of the most common mental health disorders today. They are a consequence of our lifestyles and chronic stress. But it is also possible that nutritional deficiencies, resulting from the Western way of life and chronic micronutrient deficiencies (especially minerals), are another factor behind the increased incidence of anxiety and depression. Indeed, research has shown that insufficient dietary intake of zinc or low blood levels of zinc contribute to the prevalence of depression among female students, and also that zinc is a necessary cofactor for the normal functioning of a number of enzymes that perform key brain functions, and is involved in several structural elements in this organ. A meta-analysis based on nine studies assessing the relationship between zinc intake and anxiety found that patients with anxiety had lower serum zinc levels. Existing research also points to a frequent zinc deficiency among psychiatric patients, indicating its importance in signalling pathways in the brain. On the other hand, we should not forget that in excessive doses, zinc is also a potent neurotoxin.

Alzheimer’s disease is a multifactorial chronic neurodegenerative disease and the most common cause of dementia, accounting for almost 95% of cases. It typically develops with age, but can also occur earlier due to a genetic predisposition. Efforts to identify its causative agents are still ongoing. One of the mechanisms proposed is a deficiency of zinc, which is normally found in large quantities in the neocortex. But opinions and research on this subject diverge considerably. Excessive amounts of zinc may actually increase the formation of beta-amyloid plaques, which one of these theories suggests are the cause of this disease. On the other hand, zinc has a neuroprotective effect and is necessary for the functioning of many enzymes in the brain. Its deficiency may thus result in reduced activity of these enzymes, including those involved in the synthesis of neurotransmitters (such as acetylcholine). When treating Alzheimer’s disease, it is therefore very important to pay attention to the doses of zinc used, so as not to achieve the opposite effect.

Multiple sclerosis (MS) is an autoimmune disease in which the immune system attacks the myelin sheath of nerve fibres. Zinc is a key factor in regulating the immune system. It is known for its ability to influence the activity of T cells, which are central to the inflammatory response in MS. Research has demonstrated that zinc can regulate inflammatory processes, which may benefit MS patients, since inflammation is one of the main drivers of disease progression. However, as with Alzheimer’s disease, it should be remembered that excessively high levels of zinc in the system can have a negative effect.

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