Selenium and diet

Selenium and nutrition

For over 50 years, selenium is recognized as an essential nutrient for animals and birds.

Syndromes have been described well defined deficiency in domestic animals and poultry, but even just 40 years ago had not even established beyond doubt the fact that Selenium is also essential for humans.

The diseases and deaths due to a deficiency of selenium have since been identified in humans. The first data obtained on the essential nature of this phenomenon came in much of China, where the population of Keshan, an area in which the soils are extremely poor in selenium, showed a high level and a high incidence of a heart ailment , due to wear of the heart muscle.

The nutritional supply of selenium is arousing great interest, because every day is appreciating more clearly than its relative deficiency may be associated with an increased risk of developing cancer, cardiovascular conditions, certain problems in responsiveness immune system and certain types of arthritic diseases. However, it has not been shown that selenium may be a helping factor in preventing these conditions, or that you could be useful in treatment, by virtue of its properties as an anti-oxidant. Could have beneficial properties by nature.

Dietary intake and the level of selenium

Selenium is transferred efficiently through the food chain soil-plant-animal-human, so that geographical differences in the availability of selenium in the soil, for uptake by plants, has much to do with most variations in the content of selenium in food (1). Most of the plants grown for food does not have any kind of requirement of selenium, and the quality of the plant does not reflect its selenium content, and we can not assume that healthy plants are full of this trace mineral. However, in most of Europe, humans do not depend entirely on plants and animals produced in the country, and thus a selenium-poor soil may not show the same degree reflected in the human species. However, the differences that appear in the blood serum of selenium on the state of the population seem to reflect the availability of selenium in the soil, which is the reason for the existence of quite marked differences in the content of selenium in blood serum selenium-rich countries and poor in selenium (2).

These intakes are reflected in the blood levels and the body of the inhabitants, the lowest are in the areas of Keshan disease in China, New Zealand and Scandinavia, the highest in Venezuela, in South Dakota, USA, and selenosis areas in China. The trace mineral levels in the body, in the New Zealanders are only 3-6 mg, compared to those of citizens of the United States amounting to 13 to 20 mg (3)

The average daily intake in mg are 150.7 in Canada (the range in the entire country is 98.3 to 224.2), 21 in Egypt, 88.3 to 207.8 in Japan. 28 to 56.2 in New Zealand, 60 in the UK and in the USA from 132 to 325.8 (4).

It is important to know the levels of selenium in blood serum and in the body in different population groups, since, as discussed below, low levels have been associated with other serious diseases in epidemiological investigations. Many problems remain, however, in terms of increasing levels of selenium in blood serum in those who are deficient in this trace mineral. Two routes have been examined; supplements given directly to individuals or introduce extra selenium in the diet by administration to fertilizer plants that contain the trace mineral. The first approach relies largely on the bioavailability of many forms of supplemental selenium are available.

Bioavailability of Selenium

Selenium different sources have been widely investigated, particularly the comparison between inorganic and organic forms. Selenium exists in the inorganic form as selenite or selenate like. In organic form selenium comes as Se-methionine, Se-cysteine, or selenium-yeast.

Robinson (6) and Thomson (7) have studied selenium absorption by the human body.

Approximately 60% of the sele-nite and about 90% of the selenate are absorbed in the intestine. Selenite is probably absorbed by passive diffusion, and it is selenate by a mechanism similar to sulfates. Selenites excretion is 40%, and that of selenates is approximately 70%. Net absorption is, therefore, approximately 30%, a value which proves to be relatively high for a mineral, compared to iron and zinc.

The inorganic selenium is absorbed to a lesser extent (60-90%) than organic selenium (75-97%), but their influence on glutathione peroxidase of blood is equally effective (8). Selenite has been tested in animals and shown to be very effective, and increases the activity of enzymes (9) significant extent.

The seleno-methionine appears to be absorbed by the same mechanism that methionine, an essential amino acid. As the only difference between them is the replacement of the sulfur in the past by the selenium in the first, this fact would be expected. The selenium-methionine is probably the preferred supplemental form. The organism is probably unable to distinguish between forms of sulfur and selenium.

One study was performed by Levander key (10), who found that selenium in the plasma and red blood cells in the blood increases considerably after digestion rich in selenium yeast and selenium-rich wheat and, as in lesser extent, after the selenates. However, the activity of glutathione peroxidase platelets increases rapidly in groups of wheat and selenate, but more slowly in the group of the yeast. This and other research has led to a model describing selenium metabolism.

This model has been invented by Burk (11), and explains most of the differences in selenium metabolism. Selenium inorganic forms of selenium directly added to a soluble food common background, while organic forms must first be catabolized. If the body has an oversupply of protein, some amino acids are used for purposes other than that of the formation of proteins. And so goes the selenium released soluble dietary common background. Conversely, if you are making links protein, the selenium-methionine becomes part of the background disappears proteins and food stuffs. But, ultimately, these proteins are catabolized and thus selenium is released slowly. The proteins can, therefore, be considered as a second common depth less easy food mobilization. Selenium used for biosynthesis of glutathione peroxidase background is probably derived soluble food stuffs. Subsequent research has confirmed this theory using animal models. Also, in animals, the methionine content in the diet has proven an important factor which influences the absorption of selenium. Low levels of methionine reduce the absorption of this mineral.

The in vitro effectiveness of some inorganic and organic compounds of selenium, as substitutes glutathione peroxidase has been evaluated by Tarini (12), it has been found that the enzyme activity decreases in the following order: selenite> Se-cysteine > selenate> Se-ethionine> Se-methionine> selenium cyanate. This result is probably due to the loss of the common effect of dietary background.

A more recent study, performed on Finnish men, makes a comparison between the selenium yeast supplementations of selenite and selenate in terms of levels of selenium glutathione peroxidase of blood platelets in plasma levels of blood and red blood cells (13). A daily supplementation of 200 ug of selenium during 16 weeks in one of its forms (plus placebo) indicates that the selenites and the selenates, but not selenium yeast, 30% increase in the activity of glutathione peroxidase platelets in the blood, compared with placebo by much less than the 70% found in previous studies.

The selenium yeast and selenium in selenite increase the plasma after 11 weeks of supplementation, from 1.39 umol / l to maximum values ​​of 2.15 and 1.58 umol / l respectively. Only selenium yeast became incorporated into red blood cells. The concentration of selenium in blood plasma, which had to reach a peak of activity of glutathione peroxidase platelet was 1.25-1.45 umol. Therefore, with the current intake of 100 mg / day in Finland, the activity of glutathione peroxidase is saturated in the plasma and red blood cells, and platelets almost saturated.

Ascorbic acid (vitamin C) may have a beneficial effect on the bioavailability of selenium (14), as measured by blood plasma levels and the activity of glutathione peroxidase in plasma.

Four weeks of supplementation with 50 ug of selenium tid with meals, with and without 200 mg of ascorbic acid, indicated that the blood plasma levels were increased significantly over those treated with selenium in the form of sodium selenate, in those taking this amount of trace mineral as selenate more ascorbic acid, and in those treated with ascorbic acid alone. The highest levels were found in those who had taken selenium and ascorbic acid, and the lowest were those of patients treated with ascorbic acid alone. The activity of glutathione peroxidase blood responded similarly.

These results suggest that ascorbic acid has a beneficial effect on the bioavailability of selenium in foods with less effect on supplemental selenium in the form of selenate. Selenium is present in many foods ways, some of which are best absorbed in the presence of ascorbic acid. There is absolutely no argument in support of organic forms, although many pharmaceutical firms have promoted these substances as the only effective. Thus, both the organic and inorganic forms have the ability to provide essential selenium body.

Technically, selenates that selenites are best because of their chemical stability. Finland has one of the lowest dietary intakes of selenium worldwide and in an attempt to remedy this situation, an experiment was undertaken, which was added to the mineral fertilizers used on crops. In the group of men studied, their dietary intake was increased from 40 to 100 micrograms of selenium daily when fed agricultural products with selenium supplementation. The communication we have discussed (13) was a track that study, using the same group of men.

Since, with this intake, platelets, plasma and red blood cells, the activity levels of glutathione peroxidase are near or at their peak, this should be enough to cover the physiological and biochemical everyday . However, now analyze the relationship between intake of selenium and prevention of diseases, in cases where the amounts would be higher may be necessary for therapeutic purposes.

Source: Dr Leonard Mervyn.

References

1. Levander. A.O. In Selenium in Selenium-Telluriurn Foods in the Environment, p.22-26, Pittsburgh. P.A. S Industrial Health Foundation, 1976.
2. Schrauzer, G.N and WHITE, D.A. Selenium in Human Nutrition. Bioinorganic Chem, 8, 303-18..1978.
3 CASEY. C.E. and others. Selenium in Human Tissues. Arch of Environ. Health. 37, p.133-35, 1982.
4. D1PLOCK, A.T. Trace elements in human health with Special Reference to Selenium. Anter.J.Clin.Nutr.; 45. p.1313-22, 1987.
5. THORLING, E.B. and others. Annals of Clinical Research, 18. p.3-7, 1986.
6. ROBINStAlsIoM.F. and THOMSON, C.D. The role of selenium in the diet. Nutr.Alst.Rev., 53. p.3-26. 1983.
7. THONISON, C.D. and ROBINSON, M. F. Urinary and fecal excretion and absorption of a large supplernent of selenium: superimity of selenate to selenite. Amer.J.Clin.Nutr .. 44, p.659-62. 1986.
8. Mutanen. M. Bioavailability of selenium. Annals of Clinical Research, 8, p.3-7. 1986.
9. SUNDE. R.A. and others. Effect of dietary methionine on the selenite and selenomethionine biopotency of in the rat "J.Nutr., 111, p.76-86, 1981.
10. Levander, A.O. and others. Bioavailability of selenium to Finnish niel) as Assessed by platclet acti-vity peroxida.se glutathione and other blood paraineters. Amer.J.Clin.Nutr., 37, p.887-97, 1983.
11. Burk, R.F. Selenium and cancer: rneaning of selenium levels. J.Nutr .. 116, p.1584-86, 1986.
12. Tarini, J.Z. Evaluation of selected organic and inorganic selenium compounds for selenium-dependent glutathione but-xidase activity. Nutr.Rep.Inst .. 33. p.299-306, 1986.
13. Alfthan, G. and others. Selenium metabolism platelet glutathione peroxidase activity asid in healthy Finnish men: effeets of selenium yeast, selenite and selenate. Amer.J.Clin.Nutr. "53. p.120-5. 1991.

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