Dietary Reference Intakes for Vitamin C, Vitamin E, Selenium, and Carotenoids (2000) / Chapter Skim
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7 Selenium
7 Selenium
Pages 284-324
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From page 284... ...
for selenium is based on the amount needed to maximize synthesis of the selenoprotein glutathione peroxidase, as assessed by the plateau in the activity of the plasma isoform of this enzyme. The RDA for both men and women is 55 fig (0.7 ~mol)
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From page 285... ...
Other selenoproteins have not yet been characterized to the same extent with respect to function (Behne et al., 1997~. Thus, the known biological functions of selenium include defense against oxiciative stress, regulation of thyroid hormone action, and regulation of the rebox status of vitamin C and other molecules.
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From page 286... ...
The amount of selenium macle available to the organism from this pool is a function of turnover of the methionine pool and not the organism's need for selenium. The second reserve pool of selenium is the selenium present in liver glutathione peroxiciase (GSHPx-l)
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From page 287... ...
It is possible that this disease, like Keshan disease, occurs only in selenium-deficient people. However, there has been no demonstration that improvement of selenium nutritional status can prevent Kashin-Beck disease, so involvement of selenium deficiency in its pathogenesis remains uncertain.
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From page 288... ...
In aciclition to a low selenium intake, low blood and hair selenium concentrations are associated with Keshan disease. The disease occurs with varying frequency in areas of China where the population is severely selenium deficient (Ge et al., 1983~.
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From page 289... ...
Above these values, the plasma selenium concentration is highly clependent on the chemical form of the element ingested. Glutathione Peroxidases and Selenoprotein P in Blood Several selenoproteins are present in blood.
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However, since an assay for it is not widely available at present, the ciata for selenoprotein P are insufficient to use it to estimate a clietary requirement. Cancer In some animal models, high selenium intakes recluce the inciclence of cancer (Ip, 1998~.
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From page 291... ...
They can not, however, serve as the basis for determining clietary selenium requirements at this time. Other Measurements Urine Attempts have been macle to use urinary selenium excretion as an inclex of selenium status.
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From page 292... ...
Thus, a gentler effect in susceptibility to this disease may be present at extremely low selenium intakes, but no such effect has been clemonstrateci at current intakes. Given women's apparently increased susceptibility to Keshan disease, selenium requirements for the various age groups are baseci on male reference weights.
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From page 293... ...
Average selenium concentrations of human milk consumed by infants at different ages are shown in Table 7-1. In general, the selenium content of human milk is highest in colostrum (33 to 80 fig t0.4 to 1.0 Drool]
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294 DIETARY REFERENCE INTAKES TABLE 7-1 Selenium Content of Human Milk Selenium Content Materna: Reference of Milk (pg/L) Stage of Lactation Intake (l Shearer and 18 (7-60)
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From page 295... ...
n = 22 Japanese healthy full-term infants and their mothers, aged 22-34 Women were from the same geographical area Wide interindividual variation in milk Se content Also measured serum level: mean serum level in mothers at 3 mo pp = 14.8 + 4.7 1lg/dL; level in control subjects = 13.5 + 1.9 1lg/dL n = 13 Finnish human milk-fed infants and their Dietary intake based on 7-d food records n = 46 human milk samples from 31 Finnish mothers 100 (yeast-Se n = 200 Finnish healthy full-term infants and their supplement) mothers Three groups: no supplement, 100 1lg/d yeast-Se, and 100 ~g/d selenite.
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b Lack of correlation between human milk and serum selenium concentration. c SD = standard deviation.
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From page 297... ...
There was a negative correlation between parity and milk Se during late lactation regardless of season Protein, GSHPx, and Px were not affected by state of lactation or parity n = 20 Australian human milk-fed infants and their mothers, aged 17-38 Hind milk Se was significantly greater than fore milk Se Blood and serum Se also measured n = 50 German healthy term infants exclusively fed human milk No change in plasma Se from birth to 4 mo Significant decrease in erythrocyte and plasma GSHPx activity from birth to 4 mo e Positive correlation between human milk selenium and GSHPx. f GSHPx = selenium-dependent glutathione peroxidases.
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From page 298... ...
The selenium content of mature human milk remains relatively constant cluring the first year of lactation (Debski et al., 1989; Funk et al., 1990)
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Given the reported slightly increased susceptibility of females to developing Keshan disease, selenium requirements for the various age groups are baseci on the higher reference weights for males. The EAR is thus cletermineci baseci on the same criteria of aclequacy as adults, that of selenium intakes that would be expected to maximize plasma glutathione peroxidase activity.
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From page 300... ...
/day of selenium 14-18 years 55 fig (0.70 ~nol) /day of selenium Adults Ages I 9 through 50 Years Evidence Considered in Estimating the Average Requirement Twenty years ago, efforts to estimate human selenium requirements could produce only an estimated safe and adequate daily
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From page 301... ...
/clay in this population. Table 7-2 compares plasma selenium concentration, glutathione peroxiciase activity, and selenoprotein P concentrations in boys age ci 8 to 12 years and adult males residing in a Keshan disease area with corresponding values in a nearby area free of the disease.
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(1989) found that Keshan disease can occur in populations that have a plasma glutathione peroxidase activity in men that is 37 percent of maximum values.
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From page 303... ...
/day and plasma glutathione peroxidase activities that were approximately 35 percent of the values reached after supplementation with the maximum amount of selenium. The men were stuclieci in groups of eight to nine and were given selenium supplements of 0, 10, 30, 60, and 90 fig (0, 0.13, 0.38, 0.76, 1.14 mol)
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From page 304... ...
Given the reported greater susceptibility of women to develop Keshan disease and the fact that the ciata used to set the EAR came largely from men, selenium requirements for both males and females are baseci on the higher reference weights for males. EAR for Men 19-30 years 31-50 years EAR for Women 19-30 years 31-50 years 45 fig (0.57 ~nol)
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From page 305... ...
/day of selenium Adults Ages 5 ~ Years and Older Evidence Considered in Estimating the Average Requirement Adults ages 51 years and older appear to have the same selenium requirement as younger adults. No pathological conditions related to selenium insufficiency have been reported in older inclivicluals, and markers of selenium status in blood do not differ by age or gender (Hill et al., 1996~ .
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However, the pregnancy requirement should allow accumulation of enough selenium by the fetus to saturate its selenoproteins. Baseci on an estimated selenium content of 250 fig (3.2 ~mol)
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From page 307... ...
/day of selenium Lactation Evidence Considered in Estimating the Average Requirement As previously noted, human milk selenium concentration appears to be about 18 fig (0.23 ~mol) /L in Canada and the United States (Levancler et al., 1987; Mannan and Picciano, 1987; Shearer and Hacljimarkos, 1975; Smith et al., 1982~.
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From page 308... ...
This means that wheat grown in a low-selenium soil will have a low selenium content, whereas the same wheat variety grown in a high-selenium soil will have a high selenium content. For this reason, food tables that reflect average selenium contents are unreliable.
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Dietary intake of selenium in the United States and Canada varies by region but is buffered by the food distribution system. Thus, extensive transport of food throughout Canada and the United States prevents low-selenium geographic areas from having low dietary selenium intakes.
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Serum Concentrations Information from NHANES III on serum selenium concentrations in a free-living population is given in Appendix Table F-3. Serum or plasma selenium concentrations greater than the 0.8 to 1.1 ~mol/L (7 to 9 ~g/ciL)
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In light of evaluating possible benefits to health, clinical trials of closes above the UL should not be cliscourageci, as long as subjects participating in these trials have signed informed consent documents regarding possible toxicity and as long as these trials employ appropriate safety monitoring of trial subjects. Also, the UL is not meant to apply to inclivicluals who are receiving selenium uncler medical supervision.
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From page 312... ...
Chinese investigators have correlated blood selenium concentrations with clietary intakes from high-selenium foodstuffs (Yang and Zhou, 1994~. High intakes of selenium in the form of selenomethionine, the major form of selenium in food, leaci to large increases in tissue selenium concentrations.
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From page 313... ...
to have overt signs of selenosis: hair loss and nail sloughing. Because the same patients were stuclieci at different times while consuming the same food form of selenium, blood levels of selenium can be compareci and clietary intakes can be inferred from blood selenium concentrations.
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From page 314... ...
(1991) stuclieci 142 ranchers, both men and women, from eastern Wyoming and western South Dakota who were recruited to participate and were suspected of having high selenium intakes baseci on the occurrence of selenosis in livestock raised in that region.
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From page 315... ...
There are several approaches for estimating a UL in human milk-fecT infants (Levancler, 1989~. However, the most conservative approach is to use the data of Shearer and Hadjimarkos (1975~.
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Mean human milk selenium content was 46 fig (0.6 ~mol) /L in Caracas compared to 60 and 90 fig (0.8 and 1.1 ~mol)
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Water selenium content is usually trivial compared to food selenium content. However, irrigation runoff water has been shown to contain significant amounts of selenium when the soil irrigated contains large amounts of the element (Valentine et al., 1978~.
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RESEARCH RECOMMENDATIONS FOR SELENIUM · Biomarkers for use in assessment of selenium status are needed to prevent selenium deficiency and selenium toxicity. The relationship of plasma selenoprotein concentrations to graded selenium intakes must be studied in a severely selenium-deficient population in order to establish a more precise dietary selenium requirement.
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1991. Partial sequence of human plasma glutathione peroxidase and immunologic identification of milk glutathione peroxidase as the plasma enzyme.
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1990. The impact of gestational length on human milk selenium concentration and glutathione peroxidase activity.
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1986. Sequential study on glutathione peroxidase and selenium contents of human milk.
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1987. Influence of maternal selenium status on human milk selenium concentration and glutathione peroxidase activity.
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1982. Selenium intakes and status of human milk and formula fed infants.
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1989. Biochemical studies of a selenium-deficient population in China: Measurement of selenium, glutathione peroxidase, and other oxidant defense indices in blood.
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