硒营养与人体健康

硒是人体不可缺少的微量元素，硒营养与机体免疫功能，抗氧化能力等密切相关，通过对硒营养状态的评价，对大多数人而言，适当地增加硒的摄入量，对维持身体健康、预防某些疾病发生具有积极的意义。     

Selenium supplementation of symptomatic human immunodeficiency virus infected patients

The mean whole blood selenium levels in male San Diego, CA patients with acquired immune deficiency syndrome (AiDS) are 0.123 +/- 0.030 micrograms/mL (n = 24), and 0.126 +/- 0.038 micrograms/mL (n = 26) in patients with AIDS-related complex (ARC), compared to 0.195 +/- 0.020 micrograms/mL (n = 28) in San Diego healthy controls (males). To establish whether intestinal absorption of dietary selenium is impaired in AIDS or ARC, a supplementation trial was conducted in which 19 symptomatic HIV-antibody positive male patients with AIDS or ARC were taking 400 micrograms of selenium/d in form of selenium yeast for up to 70 d. The mean whole blood Se levels increased to 0.28 +/- 0.08 micrograms/mL after 70 d of supplementation, the selenium supplements were well tolerated. A rationale for adjuvant selenium supplementation of symptomatic and asymptomatic HIV carriers is proposed.     

Selenium supplementation and ischemia-reperfusion injury in rats

Cardiac ischemia--reperfusion injury results in oxidative stress and poor physiological recovery. This study examined the amount of lipid and protein oxidation during ischemia-reperfusion to assess the degree of oxidative stress. Selenium supplementation was used to alter the antioxidant status of rats and the recovery of myocardial function post ischemia-reperfusion was investigated. Male Wistar rats were fed diets containing 0, 50, and 1000 microg/kg sodium selenite for 5 weeks, whilst controls received normal rat food containing 240 microg/kg selenium. Langendorff-perfused hearts were subjected to 22.5 min global ischemia and 45 min reperfusion, with functional recovery assessed. Heart tissues were assayed for the presence of lipid peroxides and protein carbonyls and correlated to cardiac recovery. Following ischemia and reperfusion there was a significant increase in both protein oxidation and lipid peroxidation. Hearts from selenium-deficient animals demonstrated higher levels of both protein carbonyls and lipid peroxides and were more susceptible to ischemia-reperfusion injury when compared to controls (38% versus 47% recovery of rate pressure product (RPP)). Selenium supplementation lowered the levels of protein carbonyls and lipid peroxides and resulted in improved recovery of cardiac function post ischemia-reperfusion (57% recovery of RPP). These data suggest that selenium supplementation may provide an effective method for reducing oxidative damage post cardiac ischemia-reperfusion.     

Selenium in total parenteral nutrition

In clinical practice, selenium deficiency may arise under conditions of chronic malnutrition and especially after long-term total parenteral nutrition (TPN). In infants receiving long-term TPN, we observed plasma selenium levels as low as those previously reported in Chinese children with Keshan disease. Low plasma selenium levels were also usually associated with very low activities of glutathione peroxidase. Although clinical symptoms of selenium deficiency did not occur in our patients, several cases have been described in the literature, indicating the need for supplementation in TPN. In order to derive at the appropriate dosage, it is proposed to correlate it with the total protein supply. According to our present knowledge, .5–1.0 μg selenium/g of protein appears to be adequate to keep patients in Se balance. For Se repletion of body stores, this dosage has been increased up to 3 μg of Se/g of protein. Advantages and disadvantages of selenite and of selenomethionine as possible supplemental forms of Se for TPN solutions are discussed.     

The effects of dietary chromium supplementation on some blood parameters in sheep

The effects of dietary inorganic chromium on some biochemical parameters were determined in lambs fed either a control diet or a 200-ppb or 400-ppb chromium-supplemented diet. The live weight of the animals were measured and jugular blood samples were collected prior to supplementation (d 0) and on d 20, 40, and 55. On d 55, three animals from each group were slaughtered to measure subcutaneous fat. Sera were analyzed for glucose, triglyceride, total cholesterol, high-density lipoprotein (HDL) and low-density lipoprotein (LDL) cholesterol, total protein, albumin, ALT, AST, and GGT levels. Chromium supplementation had no significant effect on live weight, but subcutaneous fat was reduced significantly in both chromium groups. There was a slight decrease in glucose concentrations in the 200-ppb chromium group, although only the differences on d 55 were significant. Triglyceride levels in both chromium groups were lower than the control group with marked differences in the 400-ppb chromium group. HDL cholesterol levels increased in both treatment groups compare to control, although the differences in the 400-ppb chromium group on d 40 were significant. Serum Cr concentrations slightly but not significantly increased in both chromium groups. No significant differences were found in total and LDL cholesterol, total protein, albumin, ALT, AST, and GGT levels. In conclusion, chromium supplementation may affect carbohydrate and lipid metabolisms and lipid deposition in lambs.     

Adequacy of dietary intakes and poverty in India: Trends in the 1990s

Linear programming methods, indicators of nutritional adequacy from the Indian Council of Medical Research and household expenditure survey data from the National Sample Survey Organization were used to construct poverty lines for India. Poverty ratios were calculated for 1993--1994 and 1999--2000 on the basis of nutritional adequacy poverty lines and compared to official estimates of poverty based on energy requirements. Nutritional adequacy poverty lines are higher than official poverty lines, particularly in rural areas. The application of nutritional adequacy poverty lines points to greater rural-urban poverty differences than in official estimates. Declines in rural poverty during the 1990s were also slower under the nutritional adequacy definition, especially in south India. There is a greater degree of rural-urban and regional bias in nutritional adequacy poverty reduction than suggested by official data. Inter-state variations in changes in nutritional poverty and official poverty in the 1990s are largely explained by differences in assumptions on overall price movements. However, relative price movements in food items also played a role, particularly the slow increase in prices of cereals and edible oils in comparison to the prices of pulses, and in some southern states, compared to milk and vegetable prices as well.     

Tissue-specific effects of chronic dietary leucine and norleucine supplementation on protein synthesis in rats

Acute administration of leucine and norleucine activates the mammalian target of rapamycin (mTOR) cell-signaling pathway and increases rates of protein synthesis in a number of tissues in fasted rats. Although persistent stimulation of mTOR signaling is thought to increase protein synthetic capacity, little information is available concerning the effects of chronic administration of these agonists on protein synthesis, mTOR signal transduction, or leucine metabolism. Hence, we developed a model of chronic leucine/norleucine supplementation via drinking water and examined the effects of chronic (12 days) supplementation on protein synthesis in adipose tissue, kidney, heart, liver, and skeletal muscle from ad libitum-fed rats. The relative concentration of proteins involved in mTOR signaling and the two initial steps in leucine oxidation were also examined. Leucine or norleucine supplementation was accompanied by increased rates of protein synthesis in adipose tissue, liver, and skeletal muscle, but not in heart or kidney. Supplementation was not associated with increases in the anabolic hormones insulin or insulin-like growth factor I. Chronic supplementation did not cause apparent adaptation in either components of the mTOR cell-signaling pathway that respond to leucine (mTOR, ribosomal protein S6 kinase, and eukaryotic initiation factor 4E-binding protein-1) or the first two steps in leucine metabolism (the mitochondrial isoform of branched-chain amino acid transaminase, branched-chain keto acid dehydrogenase, and branched-chain keto acid dehydrogenase kinase), which may be involved in terminating the signal from leucine. These results suggest that provision of leucine or norleucine supplementation via the drinking water results in stimulation of postprandial protein synthesis in adipose tissue, skeletal muscle, and liver without notable adaptive changes in signaling proteins or metabolic enzymes.     

Selenium supplementation and blood rheological improvement in Japanese adults

In order to study the prevention effect of selenium in the development of cardiovascular disease, we investigated the effects of selenium supplementation on the blood rheological properties. Eleven healthy adults were administered with 200 microg of selenium in the form of selenium yeast per day for 1 wk. Before and after the supplementation, serum selenium concentration, glutathione peroxidase (GPx) activity, biochemical indices, and the blood fluidity of the subjects were measured. The blood fluidity was measured using a (microchannel array flow analyzer) by the passage time of 100 microL of heparinized whole blood through the microchannel array. The selenium supplementation significantly (p = 0.001) shortened the mean blood passage time from 44.0 +/- 5.7 to 37.5 +/- 2.8 s. Serum selenium concentration significantly (p = 0.008) increased from 109.8 +/- 10.2 to 124.5 +/- 16.7 microg/L. Meanwhile, the GPx activity did not increased significantly (p = 0.058). The mean GPx activity of the subjects before supplementation was 171.0 +/- 16.1 Deltammol NADPH/min/L and 180.9 +/- 17.8 Deltammol NADPH/min/L after supplementation. Factor analysis of the passage time and biochemical indices of the subjects showed that blood fluidity improvement was related to the metabolic modification of lipoproteins during the selenium supplementation. These results showed that selenium supplementation improved the blood fluidity, without increasing the GPx activity of the subjects.     

Selenium supplementation and exercise: effect on oxidant stress in overweight adults

Both obesity and acute high‐intensity exercise increase oxidant stress levels. This study investigates whether selenium (Se) supplementation could be a potential effective therapy to reduce obesity‐associated oxidant stress and exercise‐induced oxidant stress. Ten normal‐weight (NW) (22.80 ± 0.41 kg/m²) and ten overweight (OW) healthy subjects (28.00 ± 0.81 kg/m²) were assessed during a randomized double‐blind Se supplementation study (200 µg sodium selenite/day for 3 weeks) with a 3‐week placebo control and inversion of treatment periods. Blood levels of lipid hydroperoxide (LH), superoxide dismutase (SOD), erythrocyte glutathione (GSH), and total antioxidant status (TAS), were measured at rest, pre‐, and postexercise (30 min 70% VO₂ max before and after treatment (pretreatment (week 0 and 12) and post‐treatment (week 3 or 15)). At rest, compared to placebo, Se supplementation had no significant effect on LH, SOD, GSH, and TAS levels. However, Se supplementation decreased LH levels in the OW group, immediately postexercise (?0.25 ± 0.12 µmol/l, P = 0.05) compared to placebo treatment. Postexercise, with or without Se supplementation, no changes in TAS, SOD, and GSH levels were observed in both the NW and OW group. This study has highlighted a potential benefit of Se in reducing LH levels postexercise in OW individuals. Given that oxidant stress is a predictor of coronary events, it is imperative to better understand oxidant stress‐related responses to lifestyle factors (in particular “high‐risk” population groups) and potential antioxidant therapy.     

Docosahexaenoic acid transfer into human milk after dietary supplementation: a randomized clinical trial

Docosahexaenoic acid (DHA) is important for infant development. The DHA transfer from maternal diet into human milk has not been investigated in detail. We studied the effects of DHA supplementation on the fatty acid composition of human milk and the secretion of dietary (13)C-labeled fatty acids, including DHA, into human milk. Ten lactating women were randomized to consume, from 4 to 6 weeks postpartum, an oil rich in DHA (DHASCO, 200 mg of DHA/day) (n = 5) or a placebo oil (n = 5). Dietary intakes were followed by 7-day protocols. On study day 14 a single dose of [U-(13)C]DHASCO was given orally, milk samples were collected over 48 h, and milk production was recorded. Milk fatty acid composition was determined by gas-liquid chromatography and isotopic enrichment was determined by gas chromatography- combustion-isotope ratio mass spectrometry (GC-C-IRMS). Milk DHA content did not differ between the supplemented and placebo group at study entry (0.29 vs. 0.28 wt%, median). After 2 weeks of supplementation the milk DHA content was almost 2-fold higher in the supplemented versus placebo group (0.37 vs. 0.21 wt%, P = 0.003). Cumulative recovery of [(13)C]palmitic, [(13)C]oleic, and [(13)C]docosahexaenoic acids in human milk at 48 h was similar between supplemented and placebo groups (palmitic acid 7.40 vs. 8. 14%, oleic acid 9.14 vs. 9.97%, and docosahexaenoic acid 9.09 vs. 8. 03% of dose, respectively). Notable lower recovery was observed for [(13)C]myristic acid in both the supplemented and placebo groups, 0. 62 versus 0.77% of dose.Dietary DHA supplementation increases the DHA content in human milk. DHA transfer from the diet into human milk is comparable to palmitic and oleic acid transfer.     

The deleterious effects of bed rest on human skeletal muscle fibers are exacerbated by hypercortisolemia and ameliorated by dietary supplementation

Prolonged inactivity associated with bed rest in a clinical setting or spaceflight is frequently associated with hypercortisolemia and inadequate caloric intake. Here, we determined the effect of 28 days of bed rest (BR); bed rest plus hypercortisolemia (BRHC); and bed rest plus essential amino acid (AA) and carbohydrate (CHO) supplement (BRAA) on the size and function of single slow- and fast-twitch muscle fibers. Supplementing meals, the BRAA group consumed 16.5 g essential amino acids and 30 g sucrose at 1100, 1600, and 2100 h, and the BRHC subjects received 5 daily doses of 10–15 mg of oral hydrocortisone sodium succinate throughout bed rest. Bed rest induced atrophy and loss of force (mN) and power (µN·FL·s^–1) in single fibers was exacerbated by hypercortisolemia where soleus peak force declined by 23% in the type I fiber from a prevalue of 0.78 ± 0.02 to 0.60 ± 0.02 mN post bed rest (compared to a 7% decline with bed rest alone) and 27% in the type II fiber (1.10 ± 0.08 vs. 0.81 ± 0.05 mN). In the BRHC group, peak power dropped by 19, 15, and 11% in the soleus type I, and vastus lateralis (VL) type I and II fibers, respectively. The AA/CHO supplement protected against the bed rest-induced loss of peak force in the type I soleus and peak power in the VL type II fibers. These results provide evidence that an AA/CHO supplement might serve as a successful countermeasure to help preserve muscle function during periods of relative inactivity. isotonic contractile properties; peak force and power; calcium sensitivity; essential amino acids     

Selenium supplementation of children in a selenium-deficient area in China

Keshan disease is a cardiomyopathy restricted to the endemic areas of China and seen in residents having an extremely low selenium (Se) status. Prophylactic administration of sodium selenite has been shown to decrease significantly the incidence of acute and subacute cases. The aim of the study was to assess the relative bioavailability of selenite versus organic Se-yeast in a Se-deficient area in China with a randomized double-blind double-dummy design. Healthy children (n=30) between 14 and 16 yr of age were randomized into three equal groups receiving either 200 μg/d selenite Se or 200 μg/d Se-yeast or placebo for 12 wk. Blood was drawn at baseline, 4, 8, and 12 wk and 4 wk postsupplementation. The plasma Se concentration (mean ± SD) was 0.16±0.03 μmol/L at baseline. Selenite and Se-yeast supplementation increased plasma Se to plateau values, 1.0±0.2 and 1.3±0.2 μmol/L, respectively. In red cells, Se-yeast increased the selenium level sixfold and selenite threefold compared to placebo. The relative bioavailability of Se-yeast versus selenite measured as glutathione peroxidase (GSHPx) activity was similar in plasma, red blood cells, and platelets. GSHPx activity reached maximal levels in plasma and platelets of 300% and 200%, respectively, after 8 wk compared to the placebo group, but continued to increase in red cells for 16 wk. Our study showed that although both forms of Se were equally effective in raising GSHPx activity, Se-yeast provided a longer lasting body pool of Se. Se-yeast may be a better alternative to selenite in the prophylaxis of Keshan disease with respect to building up of body stores.     

Selenium depletion in patients on home parenteral nutrition

Severe selenium (Se) depletion was found in nine patients receiving long-term home parenteral nutrition because of short bowel syndrome. Plasma Se ranged from 0–0.51 (median 0.21 μmol/L) and erythrocyte Se ranged from 0.7–2.6 (median 1.8 μmol/gHgb), which was significantly lower than in the controls. Glutathione peroxidase (GSHPx) in plasma and erythrocytes was also decreased. After bolus injections with 200 μg Se/d in the form of sodium selenite for 4 mo, followed by 100 μg/d for 8 mo, plasma Se increased to values slightly but significantly higher than in the controls. Erythrocyte Se reached normal levels in most of the patients after 4 mo substitution, but it remained lower than in the controls. Following Se supplementation, plasma and erythrocyte GSHPx did not differ between patients and controls. These data suggest that all patients receiving long-term parenteral nutrition because of short bowel syndrome should receive at least 100 μg sodium selenite/d when given as bolus injections to avoid Se depletion.     

Selenium and sulfur supplementation to steers grazing tall fescue

Forty steer calves averaging 257 kg were allotted to a randomized complete block design experiment containing 10 animals per treatment. Four tall fescue pastures of 5.7 ha each were utilized during the 84-d grazing study. Each pasture treatment block contained 10 calves. Calves were fed a control supplement of 96.9% ground corn and 3.1% trace mineral salt in two pastures, or a sulfur supplement that contained 94.3% ground corn, 3.1% trace mineral salt, and 2.5% elemental sulfur in the remaining two pastures. Each supplement was fed at the rate of 0.45 kg/head daily. One-half of the calves in each pasture were injected with 15 mg selenium (Se) as sodium selenite initially and at 28-d intervals throughout the trial. The treatments were as follows: (1) control-no sulfur, no selenium; (2) selenium, no sulfur; (3) sulfur, no selenium and; (4) selenium plus sulfur. Calf weights were monitored and certain blood parameters measured every 28 d. Average plasma Se values were increased (P < 0.001) from 0.021 ppm in calves not receiving Se to 0.043 ppm in those receiving Se. Plasma urea nitrogen levels were not affected by Se administration, but were lowered (P <0.05) from 16.6 to 15.8 mg/100 mL by sulfur administration. All plasma amino acids measured, except methionine, phenylalanine, argi-nine, and citrulline, were cleared from the blood in response to Se supplementation as reflected by their lower concentrations when compared with other treatment groups. Overall average daily gains were not significantly (P > 0.10) increased by sulfur supplementation, but were increased (P < 0.05) from 0.33 kg/d in calves not receiving Se to 0.43 kg/d in those receiving Se injections. Significant interactions between fulfur and Se were not noted.