Micronutrients for the
Micronutrients for the immune system often affected by an undersupply, as they have a comparatively high need, but at the same time have a low storage capacity. People with fat absorption disorders, such as exocrine pancreatic insufficiency, as well as diabetics and people with hyperthyroidism are also considered to be risk groups, as they cannot absorb fat-soluble nutrients well or can only convert vegetable carotenoids into vitamin A to a limited extent. As a symptom of a vitamin A deficiency, those affected often experience night blindness, an impairment of vision in dim light. Without sufficient Vitamin A, the rod cells of the eye cannot produce enough rhodopsin, which is formed from the vitamin A derivative 11-cis-retinal and the protein opsin. (Fig. 1). Fig. 1: Vitamin A is stored in the liver and the pigment epithelial cells of the retina in the form of retinyl esters. As all-trans retinol, the vitamin can be bound to so-called retinol-binding proteins and transported in the blood. If necessary, retinyl esters are hydrolyzed to 11-cis retinol and, depending on zinc, oxidized to retinal. In the rod cells of the retina, retinal is bound to the protein opsin to form the light-sensitive receptor molecule rhodopsin. The photons of the light catalyze the isomerization of the cis-retinal to trans-retinal, which separates from the rhodopsin and triggers the creation of a nerve impulse that is processed by the visual cortex in the cerebral cortex. Since the rod cells are primarily responsible for seeing in low light conditions, vitamin A deficiency is associated with the symptom of night blindness. -1,1 -2,3 -3,5 -4,7 Luminance [log cd/m 2 ] Pigment epithelium (retina) 11-cis-retinal Zn 11-cis-retinol all-trans-retinyl-ester all-trans-retinol Photoreceptor (rod) cell 11-cis-retinal Vitamin A-deficiency Rhodopsin Opsin + all-trans-retinal all-trans-retinol After therapy with daily 50.000 I.E. (15 mg) Vitamin A over 30 days normal adaption range Time in the dark [minutes] 0 10 20 30 40 Nerve impulse Vision Fig. 2: In contrast to phototopic vision, in which colours can be perceived with sufficient brightness, with so-called scoptic vision with the rods in low light conditions, no color perception is possible. Rod vision depends on the rhodopsin concentration in the rod cells. Since rhodopsin first has to be formed in the rod cells, dark adaptation takes a certain amount of time. In the case of vitamin A deficiency, rhodopsin formation is disturbed, so that vision is not possible at low luminance levels and night blindness occurs. The supplementation of 15 mg vitamin A daily for 30 days can restore normal dark adaptation. (4) It is assumed that a regular daily intake of 3 mg vitamin A (3,000 µg retinol activity equivalents) is harmless for adults (so-called tolerable upper intake level). (3) To compensate for an existing vitamin A deficiency, it can make sense to supplement higher doses over a short period of time, e. g. 15 mg of vitamin A daily for 30 days (Fig. 2). Zinc is an essential trace element for the metabolism of vitamin A. The enzyme retinol dehydrogenase, which converts 11-cis-retinol to 11-cis-retinal, as well as the enzyme beta-carotene monooxygenase, which converts beta-carotene into two molecules of retinal, depend on adequate zinc concentrations for their function. Zinc An adult’s body contains around 1.5 to 3 g of zinc, with more than 95 % of the trace element being found in the cells of the muscles (around 57 %), the bones (around 29 %) and other tissues. Only about 0.1 % of the cation is dissolved in the blood plasma or bound to albumin, with typical concentrations in the range of 1 µg/ml blood. Zinc forms a cofactor or is part of more than 300 enzymes and an even larger number of other proteins, such as transcription factors, which control the conversion of DNA into RNA. An inadequate zinc supply is associated with growth disorders, anaemia, disorders of the hormonal balance, poor wound healing and impaired vision. A zinc deficiency is also associated with a deterioration in the immune response to pathogens and an increase in the unspecific activation of T cells. As a cofactor of the enzyme superoxide dismutase, zinc plays a decisive role in the neutralization of reactive superoxide radicals, which are produced in the metabolism during reactions with oxygen (oxidative stress). According to data from the National Consumption Survey II, 21 % of women and 32 % of men in Germany do not achieve the recommended amounts of zinc through the diet. Phytic acid, which is mainly contained in pulses, cereals and oilseeds, is used by the plants as a store for cations such as iron and zinc. As Resorption of zinc [%] 25 20 15 10 5 0 0 50 Phytate [mg] 100 150 200 250 Fig. 3: Phytic acid contained in plant-based foods forms insoluble complexes with zinc and inhibits the uptake of the trace element in the small intestine. The phytate content of a meal correlates inversely with the absorption of the contained zinc. (5) 30 No. 3 November/December 2021
Micronutrients for the immune system a complexing agent, it can insoluble bind the zinc contained in the food and thereby hinder its absorption in the small intestine (Fig. 3). Depending on the phytate intake, the German Nutrition Society recommends a daily zinc intake of between 7 and 10 mg for women and between 11 and 16 mg for men. It is believed that zinc needs increase with age. In an investigation with study participants between the ages of 65 and 82 years, the daily supplementation of 10 mg zinc for seven weeks had a significantly positive effect on the immune system. An improved control of the immune response could be shown, which was expressed in a reduction of proinflammatory metabolic parameters with simultaneously improved immune defense. According to this, dietary supplementation with zinc does not lead to a general inhibition of the immune response compared to certain anti-inflammatory pharmacotherapies. Zinc improves the immune response to pathogens and reduces the incidence of infections. (6) Vitamin D Vitamin D plays important roles in maintaining calcium levels in the blood and in building and maintaining our bones. In addition, it is of central importance for the regulation of the immune response by T helper cells. Vitamin D reduces the formation of Th1 helper cells, which are held responsible for excessive immune reactions, such as those that occur in autoimmune diseases. (7) Vitamin D promotes the formation of Th2 helper cells and regulatory T cells, which suppress excessive activation of the immune system and enable adequate selftolerance. An undersupply of vitamin D goes hand in hand with a significantly increased risk of bone diseases, infections and many other diseases. Vitamin D is formed in the skin by radiation from the sun. Contrary to an often published opinion, however, in the latitudes of Germany, vitamin D formation through UV exposure of the skin is not possible from October to March, since the solar radiation hits the earth’s surface too flat and the relevant UV-B portion of the radiation is absorbed by the atmosphere. (8) Vitamin D is found in certain foods. The amounts ingested are usually too small to influence the vitamin D level to a relevant extent. Due to our modern way of life, in which we are usually not sufficiently exposed to the sun, inadequate supply is widespread also in the summer months. It is assumed that around 40 % of the European population are affected by a deficient vitamin D supply (< 30 ng/ml 25(OH)vitamin D3) or that around 13 % have a severe deficiency (
