Selenium

[Guest guest]

As we know, selenium can be

an issue for some of us in obtaining the RDA.

I did a little reading into selenium needs and how the levels were set.

From the NAS

(Note: Keshan disease is one of the main concerns of low selenium. EAR

= Estimated Average Requirement)

"Surveys in China have compared per capita daily selenium intakes of

adults in Keshan disease areas with intakes in adjacent areas that were

free of the disease (Yang and Xia, 1995; Yang et al., 1987). Adult

subjects living in the affected areas were found to have selenium

intakes of 11 µg (0.14 µmol)/day or less, while those living in

unaffected areas had intakes of 17 µg (0.22 µmol)/day or more. Thus,

based on one Chinese study, no selenium-responsive disease is known to

occur in populations with adult intakes as low as 17 µg (0.22

µmol)/day.

Additional results from China and elsewhere indicate that intakes of 20

µg (0.25 µmol)/day and greater protect adults against the development

of Keshan disease (Yang et al., 1987). In New Zealand and Finland,

intakes by adults as low as 25 µg (0.32 µmol)/day have been reported

without the occurrence of Keshan disease (Griffiths, 1973; Varo et al.,

1994)."

Also..

Based on the criterion of maximizing plasma glutathione peroxidase

activity, the data described above support a selenium EAR of 45

µg/day

for the age group 19 through 50 years based on the weights of North

American men. Given the reported greater susceptibility of women to

develop Keshan disease and the fact that the data used to set the EAR

came largely from men, selenium requirements for both males and females

are based on the higher reference weights for males.

The RDA for selenium is set by assuming a coefficient of variation

(CV) of 10 percent (see Chapter 1) because information is not available

on the standard deviation of the requirement for selenium; the RDA is defined as equal to the EAR plus

twice the CV to cover the needs of 97 to 98 percent of the individuals

in the group there fore, for selenium the RDA is 120 percent

of the EAR). The calculated RDA is rounded to the nearest 5 µg.

As a result, they set the RDA at 55

From the FAO

" Starting at frankly deficient levels, total daily selenium intakes

of above 41 µg/day were

found sufficient to increase plasma GSHPx substantially and to saturate

plasma activity in 60-kg male subjects within 5-8 months. It was

estimated that satisfactory levels of plasma selenium (>80 µmol/l)

and of GSHPx (>0.3 mmol NADPH oxidized/min/l; approximately

two-thirds of plasma saturation activity) indicative of adequate selenium reserves would be

attained after intakes of approximately 27 µg/day by

65-kg male subjects (86). Such criteria satisfying the definition

of

average normative requirements for selenium have been used as the

basis for calculating recommended nutrient intake (RNI) values in this

report after interpolating estimates of average requirements by

allowing for differences in weight and basal metabolic rate of age

groups to up to 65 years and adding a 25 percent increase (2 x assumed

SD) to allow for individual variability in the estimates of RNI (Table

52).

As a result the FAO's Recommended nutrient intake sets the level for

adult males at 34. (27 x 1.25=33.75, rounded up to 34)

So, it seems a level of 17 to 25 may be closer to what a true "minimum"

level is and 27 to 34 may be more of a "adequate intake", where is the

55 are the safer number recommended to the general population..

Jeff