Are there functional consequences of a reduction in selenium intake in UK subjects?

Dietary Se levels in the UK have fallen over the last 20 years and recent surveys indicate that average Se intakes are 30-40 microg/d, which is well below the current UK reference nutrient intake for adult men (75 microg/d) or women (60 microg/d). Functional consequences of this decline have not been recognised, although epidemiological data suggest it may contribute to increased risk of infections and incidence of some cancers. Previous data have indicated that biochemical changes in Se-dependent proteins occur in otherwise healthy UK subjects given small Se supplements. The current studies have focused on the effect of small Se supplements on the immune response since there is evidence of specific interactions between Se intake and viral replication, and since the potential anti-cancer effects of Se may be mediated by non-antioxidant effects of Se such as changes in immune function. Data indicate that subjects given small Se supplements (50 or 100 microg Se/d) have changes in the activity of Se-dependent enzymes and evidence of improved immune function and clearance of an administered live attenuated virus in the form of poliovirus vaccine. Responses of individual subjects to Se supplements are variable, and current work is evaluating potential explanations for this variability, including genetic variability and pre-existing Se status.     

三代繁殖低硒和低硒低碘大鼠动物模型的建立

目的　建立三代繁殖低硒大鼠动物模型 ,为了进一步系统研究低硒对大鼠脑神经智能、心血管、骨软骨、免疫器官 ,生长发育以及生育、衰老的影响提供研究用动物模型。方法　利用低硒酵母为主要原料人工配制半合成饲料喂养大鼠并连续繁殖到第三代 ,历时一年半。原代动物选用健康断乳后封闭群SD大鼠6 0只 ,体重平均值为 (5 0± 5 )g。作为F0代 ,五组大鼠分别为 1 合成饲料对照组 (硒水平 0 1～ 0 3μg g,碘水平≥ 0 2 μg g) ,2低硒一组 (硒水平 0 0 2 μg g,碘水平≥ 0 2 μg g) ,3 低硒二组 (硒水平 0 0 0 5 μg g ,碘水平≥0 2 μg g) ,4 低碘组 (硒水平 0 1～ 0 3μg g ,碘水平 0 0 4 μg g) ,5 低硒低碘组 (硒水平 0 0 1μg g ,碘水平0 0 4 μg g) ;雌雄分笼饲养。F1、F2、F3的分组为 :取消低硒二组 ,低硒低碘组饲料中硒水平同单纯低硒组、碘水平同单纯低碘组 ,余同原代。雌雄分笼饲养。每代大鼠检测血清硒水平、全血GPX活性 ,血清总T3、T4、TSH水平 ,同时对各代仔鼠生长发育期体重、分娩数、新生鼠存活数等进行了观察。结果　发现人工半合成低硒饲料可持续保持大鼠低硒状态 ,使血清硒值在三代繁殖大鼠中维持低水平 ;全血GPX活性保持低水平 ;低硒大鼠分娩数、新生仔鼠存活率下降 ,体重减?     

Biofortification of UK food crops with selenium

Se is an essential element for animals. In man low dietary Se intakes are associated with health disorders including oxidative stress-related conditions, reduced fertility and immune functions and an increased risk of cancers. Although the reference nutrient intakes for adult females and males in the UK are 60 and 75 microg Se/d respectively, dietary Se intakes in the UK have declined from >60 microg Se/d in the 1970s to 35 microg Se/d in the 1990s, with a concomitant decline in human Se status. This decline in Se intake and status has been attributed primarily to the replacement of milling wheat having high levels of grain Se and grown on high-Se soils in North America with UK-sourced wheat having low levels of grain Se and grown on low-Se soils. An immediate solution to low dietary Se intake and status is to enrich UK-grown food crops using Se fertilisers (agronomic biofortification). Such a strategy has been adopted with success in Finland. It may also be possible to enrich food crops in the longer term by selecting or breeding crop varieties with enhanced Se-accumulation characteristics (genetic biofortification). The present paper will review the potential for biofortification of UK food crops with Se.     

Urinary excretion of selenium by New Zealand and North American human subjects on differing intakes

Lower renal plasma clearances of selenium (CSe 0.1-0.2 ml min-1), indicating excretion of a smaller proportion of Se presented to the kidneys, were found in New Zealand (NZ) residents with low plasma Se ((Se)p 50-70 ng ml-1) on customary intakes below 30 micrograms d-1 Se. North American subjects consuming 80 micrograms d-1 with (Se)p 120-140 ng ml-1 had CSe between 0.2 and 0.3 ml min-1. Several weeks' supplementation with high-Se bread increased NZ subjects' (Se)p to 120-175 ng ml-1 and CSe to 0.4-0.7 ml min-1. (Se)p remained elevated when supplementation ceased, but CSe returned to the basal range within a few days. Americans' clearances showed no such abrupt decrease when their dietary intake was similarly reduced. The NZ residents thus appeared to excrete selenium more sparingly than others. Rapid alterations in clearance after supplements and single doses were probably due to changes in the proportions of different forms of selenium in the plasma.     

Bioavailability of selenium to residents in a low-selenium area of China

For 8 wk 5 groups of 10 men each were given 0.5 g/day DL-methionine, 150 micrograms Se/day as sodium selenite with or without methionine or 150 micrograms Se/day as selenomethionine with or without methionine. Twenty subjects received placebo as controls. Initially plasma Se rose more rapidly than RBC Se. Increases in Se levels were significantly greater with selenomethionine than with the selenite supplement. In the placebo and methionine supplemented groups neither plasma nor RBC Se varied significantly over the course of the study. Supplementation with selenium resulted in marked increases in plasma and RBC GSH-Px within 2 and 4 wk, respectively. Plasma and RBC GSH-Px activity did not differ significantly between Se-supplemented groups. These studies suggest that selenomethionine-Se was more effective in raising plasma and RBC Se than was selenite-Se. Methionine supplements may increase the bioavailability of selenium in severely deficient subjects.     

Effectiveness of selenium supplements in a low-selenium area of China

BACKGROUND: Selenium is an essential micronutrient with a recommended dietary allowance for adults of 55 mug/d. It functions as an essential constituent of selenoproteins. Although there is no evidence of selenium deficiency in the United States, people in many other areas of the world are selenium deficient, with the consequence that they are unable to express their selenoproteins fully. OBJECTIVE: We carried out a supplementation trial in a selenium-deficient population in China to assess the requirement for selenium as selenite and as selenomethionine. DESIGN: One hundred twenty subjects with an average selenium intake of 10 mug/d were randomly assigned and administered tablets containing no selenium or amounts as high as 66 mug Se/d for 20 wk. Plasma was sampled before supplementation and at 4-wk intervals during supplementation and was assayed for the 2 plasma selenoproteins, glutathione peroxidase and selenoprotein P. RESULTS: Full expression of glutathione peroxidase was achieved with 37 mug Se/d as selenomethionine and with 66 mug/d as selenite. Full expression of selenoprotein P was not achieved at the highest doses of either form. CONCLUSIONS: Full expression of selenoprotein P requires a greater selenium intake than does full expression of plasma glutathione peroxidase. This suggests that selenoprotein P is a better indicator of selenium nutritional status than is glutathione peroxidase and that the recommended dietary allowance of selenium, which was set with the use of glutathione peroxidase as the index of selenium status, should be revised. Selenium as selenomethionine had nearly twice the bioavailability of selenium as selenite.     

Serum selenium levels in Saudi new-borns

Selenium (Se) was measured in 300 umbilical cord blood samples collected from healthy pregnant women who live in Al-Kharj area in Saudi Arabia by means of Inductively Coupled Plasma Spectrometry with the hydride t-system. The selenium concentration found in the serum of 300 newborns was 40.847 ± 8.969 μpg/L. Preterm infants had significantly lower serum selenium concentrations than full-term infants (32 ± 8.029 μg/L versus 41.323 ± 8.784 μg/L). Significant positive correlations were found between selenium levels and birth weight. Results of this study suggest that low selenium levels of new-borns in Al-Kharj may reflect an inadequate maternal dietary intake.     

Brazil nuts: an effective way to improve selenium status

BACKGROUND: Brazil nuts provide a rich natural source of selenium, yet no studies have investigated the bioavailability of selenium in humans. OBJECTIVE: We investigated the efficacy of Brazil nuts in increasing selenium status in comparison with selenomethionine. DESIGN: A randomized controlled trial was conducted with 59 New Zealand adults. Participants consumed 2 Brazil nuts thought to provide approximately 100 mug Se, 100 mug Se as selenomethionine, or placebo daily for 12 wk. Actual intake from nuts averaged 53 mug Se/d (possible range: 20-84 mug Se). Plasma selenium and plasma and whole blood glutathione peroxidase (GPx) activities were measured at baseline and at 2, 4, 8, and 12 wk, and effects of treatments were compared. RESULTS: Plasma selenium increased by 64.2%, 61.0%, and 7.6%; plasma GPx by 8.3%, 3.4%, and -1.2%; and whole blood GPx by 13.2%, 5.3%, and 1.9% in the Brazil nut, selenomethionine, and placebo groups, respectively. Change over time at 12 wk in plasma selenium (P < 0.0001 for both groups) and plasma GPx activity in the Brazil nut (P < 0.001) and selenomethionine (P = 0.014) groups differed significantly from the placebo group but not from each other. The change in whole blood GPx activity was greater in the Brazil nut group than in the placebo (P = 0.002) and selenomethionine (P = 0.032) groups. CONCLUSION: Consumption of 2 Brazil nuts daily is as effective for increasing selenium status and enhancing GPx activity as 100 mug Se as selenomethionine. Inclusion of this high-selenium food in the diet could avoid the need for fortification or supplements to improve the selenium status of New Zealanders.     

Glutathione, glutathione peroxidase, and selenium status in HIV-positive and HIV-negative adolescents and young adults

BACKGROUND: Antioxidant nutrient deficiencies may hasten the progression of HIV disease by impairing antioxidant defenses. OBJECTIVE: The objective of the study was to determine whether HIV infection is associated with poor selenium status and low antioxidant protection by glutathione and glutathione peroxidase (GPX). DESIGN: In a cross-sectional study of 365 HIV-positive and HIV-negative adolescents and young adults, we examined the relation of plasma selenium, whole-blood glutathione, and whole-blood GPX to HIV status, disease severity, immune activation, and oxidative damage. RESULTS: Selenium deficiency (plasma selenium < 0.070 microg/mL) was not seen in any subjects, and plasma selenium in 244 HIV-positive subjects (0.120 +/- 0.0013 microg/mL) did not differ significantly (P = 0.071) from that in 121 HIV-negative subjects (0.125 +/- 0.0020 microg/mL) . However, multiple regression analysis after adjustment for covariates showed a significant (P = 0.002) negative association between HIV-associated immune activation (plasma neopterin) and plasma selenium concentrations. GPX activity was highest in HIV-positive subjects taking antiretroviral therapy (median: 14.2; 25th, 75th percentiles: 11.1, 18.7 U/mL; n = 130), intermediate in HIV-positive subjects not taking antiretroviral therapy (11.8; 9.4, 15.1 U/mL; n = 114), and lowest in HIV-negative subjects (10.6; 8.6, 12.7 U/mL; n = 121; P < 0.05 for all comparisons). GPX was also positively associated with malondialdehyde, a marker of oxidative damage. CONCLUSIONS: Subjects had adequate selenium status, although HIV-related immune activation was associated with lower plasma selenium concentrations. GPX activity appears to have been induced by the oxidative stress associated with HIV infection and use of antiretroviral therapy. Thus, young, well-nourished subjects can mount a compensatory antioxidant response to HIV infection.     

An estimation of selenium requirements for New Zealanders.

BACKGROUND: Current US dietary recommendations for selenium are based on maximization of plasma glutathione peroxidase (GSHPx) activity according to data from one study of Chinese men. OBJECTIVE: The effect of various amounts of supplemental selenium on GSHPx activities in blood of New Zealand adults was investigated to calculate a selenium requirement for New Zealanders. The effect on plasma selenoprotein P and thyroid hormones was also investigated. DESIGN: Fifty-two adults with low blood selenium concentrations ingested a placebo or 10, 20, 30, or 40 microgram Se as L-selenomethionine daily for 20 wk. RESULTS: Plasma and whole-blood GSHPx activities increased in all supplemented groups but reached a plateau only in the group receiving 40 microgram Se, as determined by statistical analysis. Increases in selenoprotein P were greater than those for selenium and GSHPx at all supplement intakes. Thyroxine concentrations decreased in supplemented groups but the decrease was significantly different from that in the control group only for the 10-microgram group and for all supplemented groups combined. CONCLUSIONS: An upper estimated requirement of 90 microgram Se/d was calculated as the intake necessary for maximization of plasma GSHPx activity, as used in the derivation of the US recommended daily allowance. Our lower estimated requirement of 39 microgram Se/d was the intake necessary to reach two-thirds of maximal GSHPx activity, as was used in calculating the World Health Organization normative requirement. The lower estimate is a realistic goal for New Zealand but the upper estimate could be achieved only with regular inclusion of high-selenium foods.     

Selenium intakes,absorption, retention,and status in adolescent girls

OBJECTIVES: To assess selenium intakes, absorption, retention, and status in healthy adolescent girls and the effect of calcium supplementation on selenium parameters. DESIGN: Annual 2-week study conducted each year for 3 consecutive years in which yearly selenium intakes, absorption, and retention and blood selenium status were measured. SETTING: A metabolic unit in a large metropolitan hospital located in Columbus, Ohio--a low selenium region of the United States. SUBJECTS: Healthy white girls aged 11 to 14 years (n=16) enrolled in a calcium balance study and randomly assigned to receive a placebo of methylcellulose (n=9) or a calcium supplement containing 1,000 mg supplemental calcium as calcium citrate malate (n=7). INTERVENTIONS: Each subject consumed a diet with approximately 100 microg selenium/day during the yearly 2-week balance studies. RESULTS: Selenium status measurements (serum and erythrocyte selenium and glutathione peroxidase activity) were all within normal ranges for adults during the study. Apparent selenium absorption averaged 71%, 76%, and 74% for years 1, 2, and 3 of the study, respectively, and did not vary significantly (P>.05). Average daily selenium retention did not differ among the years of the study (P>.05) and indicated that the usual selenium intake was approximately 100 microg daily. Measurements of selenium status and retention did not differ between calcium-supplemented and placebo groups. CONCLUSIONS: An intake of approximately 100 microg selenium/day is the typical intake of the mineral among the subjects and appeared adequate to maintain selenium status in these healthy adolescent girls; in addition, calcium supplementation of 1,000 mg daily does not have a negative impact on selenium parameters.     

Randomized, double-blind, placebo-controlled trial of selenium supplements among HIV-infected pregnant women in Tanzania: effects on maternal and child outcomes

BACKGROUND: In observational studies, adequate selenium status has been associated with better pregnancy outcomes and slowed HIV disease progression. OBJECTIVE: We investigated the effects of daily selenium supplements on CD4 cell counts, viral load, pregnancy outcomes, and maternal and infant mortality among 913 HIV-infected pregnant women. DESIGN: In this randomized, double-blind, placebo-controlled trial, eligible women between 12 and 27 wk of gestation were given daily selenium (200 mug as selenomethionine) or placebo as supplements from recruitment until 6 mo after delivery. All women received prenatal iron, folic acid, and multivitamin supplements irrespective of experimental assignment. RESULTS: The selenium regimen had no significant effect on maternal CD4 cell counts or viral load. Selenium was marginally associated with a reduced risk of low birth weight [relative risk (RR) = 0.71; 95% CI: 0.49, 1.05; P = 0.09] and increased risk of fetal death (RR = 1.58; 95% CI = 0.95, 2.63; P = 0.08), but had no effect on risk of prematurity or small-for-gestational age birth. The regimen had no significant effect on maternal mortality (RR = 1.02; 95% CI = 0.51, 2.04; P = 0.96). There was no significant effect on neonatal or overall child mortality, but selenium reduced the risk of child mortality after 6 wk (RR = 0.43; 95% CI = 0.19, 0.99; P = 0.048). CONCLUSION: Among HIV-infected women from Dar es Salaam, Tanzania, selenium supplements given during and after pregnancy did not improve HIV disease progression or pregnancy outcomes, but may improve child survival. This trial was registered at clinicaltrials.gov as NCT00197561.     

Soluble tumor necrosis factor-alpha receptor type 1 during selenium supplementation in psoriasis patients

OBJECTIVE: Tumor necrosis factor-alpha (TNF-alpha) and its receptors play important roles in the induction and maintenance of psoriatic lesions. Selenium (Se), a trace element with immunomodulatory properties, is usually decreased in psoriasis patients. We examined the influence of Se supplementation on soluble TNF-alpha receptor type 1 (sTNF-R1) and topical treatment in psoriasis patients. METHODS: The study was conducted in between January and June 2002. Twenty-two inpatients with active plaque psoriasis received topical treatment with 5% salicylic acid ointment, 0.1% to 0.3% dithranol ointment, and 200 microg daily of Se as selenomethionine (SeMet; n = 11, group 1) or placebo (n = 11, group 2) for 4 wk. Psoriasis Area and Severity Index (PASI) score and Se and sTNF-R1 concentrations were assessed at baseline and every 2 wk. Control sera were obtained from 10 healthy subjects. For statistical analysis, parametric tests were used, and the level of significance was set at P = 0.05. RESULTS: The baseline sTNF-R1 levels were 1.87 +/- 0.58 ng/mL (1.98 +/- 0.44 ng/mL in group 1 and 1.75 +/- 0.69 ng/mL in group 2, P = 0.34) in psoriasis patients and 1.65 +/- 0.25 ng/mL in control subjects (P = 0.17); baseline Se concentrations were 48.31 +/- 13.20 microg/L (48.31 +/- 13.20 microg/L in group 1 and 50.35 +/- 13.49 microg/L in group 2, P = 0.41) in psoriasis patients and 58.30 +/- 17.21 microg/L in control subjects (P = 0.05). A positive correlation between PASI and sTNF-R1 was noticed (r = 0.36, P = 0.04; r = 0.51 in group 1 and r = 0.18 in group 2). After 4 wk, almost complete remission of skin lesions was achieved in both groups, but the PASI score was higher in group 1 than in group 2 (4.30 +/- 3.92 and 1.67 +/- 1.17, respectively; P < 0.05). TNF-R1 levels were 1.81 +/- 0.42 ng/mL in group 1 and 1.33 +/- 0.40 ng/mL in group 2 (P = 0.01), and the correlation between PASI score and TNF-R1 level became inverse (r = -0.24 in group 1 and r = -0.59 in group 2). Se concentrations were 107.51 +/- 18.08 microg/L in group 1 and 56.83 +/- 15.32 microg/L in group 2 (P < 0.01). CONCLUSIONS: Increased level of sTNF-R1 may be an indicator of active psoriasis. Supplementation with selenomethionine was ineffective as adjuvant treatment in plaque psoriasis and may contribute to the maintenance of elevated TNF-R1 concentration in psoriasis patients despite the remission of skin lesions.     

Maternal--neonatal serum selenium and copper levels in Greeks and Albanians

AIM: To evaluate selenium (Se) and copper (Cu) concentrations in Greek and Albanian immigrant mothers and in the cord blood of their newborns. SUBJECTS AND METHODS: From 1118 Greek and 820 Albanian mothers and from the cord blood of their neonates blood was obtained for Se and Cu measurement. Se and Cu concentrations were determined in sera with graphite furnace atomic absorption spectroscopy (GFAAAS) and atomic absorption spectrometry, respectively. In all, 30 days' nutrient intakes were evaluated in both groups. RESULTS: Animal protein, Se and Cu intakes were poor in the Albanians vs the Greeks (P < 0.001). Se concentrations in the Greek mothers (68.3 +/- 8.5 microg/l) and in their newborns (37.02 +/- 8.9 microg/l) were found higher as compared with those in Albanian mothers (37.4 +/- 9.9 microg/l) and in their newborns (34.3 +/- 9.1 microg/l) (P < 0.001). Cu levels were also found higher (P < 0.001) in the Greek mothers (1687 +/- 353 microg/l) and in their neonates (449 +/- 87 microg/l) compared with those in the Albanian mothers (959 +/- 318 microg/l) and in their newborns (229 +/- 67 microg/l). Additionally, 31.5% of neonates born to Albanian women with Se concentrations less than 28 microg/l had higher Se levels (P < 0.01) than their mothers. CONCLUSIONS: The low Se and Cu levels evaluated in the Albanian mothers and their newborns could be related to their poor animal protein intake which could be the consequence of their low socioeconomic status. As an effective preventive measure, accurate dietetic strategies to assess the requirements of pregnant immigrant women for trace elements may be planned in Greece.     

Experimental selenium restriction in healthy adult humans: changes in selenium metabolism studied with stable-isotope methodology

Mechanisms responsible for selenium homeostasis were investigated in healthy adult men receiving diets adequate or low in Se (eight subjects per group). The appearance of a stable isotope of Se, 74Se, in plasma, urine, and feces was measured after oral administration of 74Se-selenite. One group received a restricted level of Se (18 +/- 1 micrograms/d) for 30 d, which resulted in a decrease in urinary, fecal, and plasma Se content compared with the group that consumed 119 +/- 1 micrograms/d. Low Se intake also resulted in decreased urinary 74Se excretion (27.2 +/- 1.4% vs 32.5 +/- 2.3% of the absorbed dose for the adequate intake), increased body retention of 74Se (74.8 +/- 3.1% vs 67.6 +/- 3.8% of the absorbed dose for the adequate group), and a contracted selenite-exchangeable metabolic pool (Se-EMP) (9782 micrograms for adequate Se and 6314 micrograms for the low-Se group; p less than or equal to 0.05). Measurement of Se-EMP may provide an additional and sensitive approach for assessing Se nutriture in human subjects.     

Effect of intermittent supplementation with selenate on selenium status of rats fed selenium-deficient diet

To examine the selenium (Se) status of rats intermittently supplemented with Se, we measured tissue Se contents and glutathione peroxidase (GPx) activities in rats fed a Se-deficient diet intermittently supplemented with selenate. In experiment 1, four groups of male 4-wk-old Wistar rats were fed a Torula yeast-based Se-deficient diet (Se content, < 0.01 microg/g) for 28 d. During the experimental period, the diet of each group was supplemented with sodium selenate (0.17 microg Se/g) for 0, 1, 2 or 7 d/wk. The tissue Se contents and GPx activities both increased gradually with an increase in frequency of the selenate supplementation, and significant linear regressions were observed between the frequency and these Se indices. In particular, the correlation coefficient in the liver and plasma indices was nearly equal to a value of 1.0. In experiment 2, three groups of rats were fed the Se-deficient basal diet for 28 d. Among these, one group was daily supplemented with sodium selenate to the Se-deficient diet at a level of 0.17 microg Se/g, and another group was intermittently supplemented with the selenate at a level of 1.19 microg Se/g for 1 d/wk. The tissue Se contents and GPx activities both were increased by the selenate supplementation and no significant difference was observed between daily and weekly supplementation in the Se indices except in erythrocyte Se. These results indicate that Se status in the growth period is dependent on total Se intake in this period and that weekly intermittent supplementation with Se can maintain adequate Se status.     

Selenium intakes in 18-64-y-old Irish adults

OBJECTIVE: To measure the intake of selenium (Se) and the contribution of different food groups to Se intake in adults aged 18-64 y in Ireland. The adequacy of Se intake in the population is also assessed. DESIGN: Food consumption was estimated using a 7 day food diary for a representative sample (n=1379; men=662, women=717) of 18-64-y-old Irish adults selected randomly from the electoral register. Se intake was estimated using updated tables of food composition. RESULTS: Mean daily Se intakes (+/-s.d.) from all sources (ie food plus supplements), and from food sources alone, for the group of Irish adults aged 18-64 y were 52 (+/-23) and 50 (+/-21) microg, respectively. Mean daily Se intake (from all sources) was significantly higher in men of all ages than women of all ages at levels of 60 and 44 microg, respectively (P<0.001). Meat/meat products (30%), bread and rolls (24%), fish/fish products (approximately 11%), and milk and yoghurt (9%) were the main contributors to mean daily Se intake. Adequacy of Se intake in population groups was estimated as the percentage of the population with mean daily Se intakes that were lower than the average requirement of 40 microg. Using this measure, 45.6% of women and 17.1% of men had inadequate Se intakes. CONCLUSION: A significant prevalence of inadequate Se intakes was observed in Irish adults. Therefore, it would seem prudent that the Se status of the Irish population be investigated at this time.     

Selenium metabolism and platelet glutathione peroxidase activity in healthy Finnish men: effects of selenium yeast, selenite, and selenate

The mean dietary selenium intake in Finland increased from 40 to 100 micrograms/d in 1987 because of the addition in 1985 of selenium to fertilizers. A selenium-supplementation study was performed in 1987 on the same men as were followed in a 1981 study that had a similar design (200 micrograms Se/d). Selenite and selenate, but not selenium yeast increased platelet glutathione peroxidase (GSHPx) activity by 30% compared with placebo, much less than the 70% found in the previous study. Selenium yeast and selenite increased plasma selenium after 11 wk from 1.39 mumol/L to peak values of 2.15 and 1.58 mumol/L, respectively. Only yeast selenium was incorporated into red cells. From a regression plot based on present and literature data, it was estimated that the plasma selenium concentration needed to achieve maximal platelet GSHPx activity was 1.25-1.45 mumol/L. At the present selenium intake in Finland, 100 micrograms/d, GSHPx activity is saturated in plasma and red cells and almost saturated in platelets.