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Thomson
The effect of selenium on thyroid status in a population with marginal selenium and iodine status.Thomson CD, McLachlan SK, Grant AM, Paterson E, Lillico AJ. Br J Nutr. 2005 Dec;94(6):962-8. [abstract only]
"The effects of Se on
thyroid metabolism in a New Zealand population are investigated,
including (a) the relationship between Se and thyroid status, and
(b) the effect of Se supplementation on thyroid status. The data
used come from two cross-sectional studies of Se, I, thyroid
hormones and thyroid volume (studies 1 and 4), and three Se
intervention studies in which thyroid hormones, Se and
glutathione peroxidase (GPx) activities were measured (studies 2,
3 and 5). There were no significant correlations between Se
status and measures of thyroid status after controlling for sex
at baseline or after supplementation in any of the studies. When
data from study 4 were divided into two groups according to
plasma Se, plasma thyroxine (T4) was lower in males with higher
plasma Se levels (P=0.009). Se supplementation increased plasma
Se and GPx activity, but produced only small changes in plasma T4
and triiodothyronine (T3):T4 ratio. In study 2, there was a
significant reduction in plasma T4 (P=0.0045). In studies 3 and 5
there were small decreases in plasma T4 and a small increase in
the T3:T4 ratio, which were not significantly different from
placebo groups. Lack of significant associations between plasma
Se and thyroid status, and only small changes in T4 suggest that
Se status in New Zealand is close to adequate for the optimal
function of deiodinases. Adequate plasma Se may be approximately
0.82-0.90 micromol/l, compared with 1.00-1.14 micromol/l for
maximal GPx activities."
Are breast-fed infants and toddlers in New Zealand at risk of iodine deficiency?Skeaff SA, Ferguson EL, McKenzie JE, Valeix P, Gibson RS, Thomson CD. Nutrition. 2005 Mar;21(3):325-31. [abstract only]
"OBJECTIVE: This study assessed the iodine status of New Zealand infants and toddlers and explored factors that might influence their iodine status. METHODS: A community-based, cross-sectional survey of 6- to 24-mo-old children was conducted in three cities in the South Island of New Zealand. Iodine status was determined by a casual urine sample. Breast-feeding mothers were asked to provide a breast milk sample for iodine determination. Caregivers collected a 3-d weighed diet record from their children to investigate associations between dietary patterns and urinary iodine excretion. RESULTS: The median urinary iodine concentration for the group (n = 230) was 67 microg/L (interquartile range 37-115) with 37% (95% confidence interval 30.5-43.4) of children having a urinary iodine concentration lower than 50 microg/L. When children were classified by current feeding method, those children who were currently formula-fed had a significantly higher median urinary iodine concentration (99 microg/L) than did children who were currently breast-fed (44 microg/L; P < 0.000). The mean iodine concentration in breast milk was 22 microg/L (n = 39). After multivariate analysis using estimates from 3-d diet records, only percentage of energy from infant formula was significantly associated with urinary iodine concentration (P = 0.005). CONCLUSIONS: This study found mild iodine deficiency in a group of New Zealand infants and toddlers. Children who consumed infant formula, which is fortified with iodine, had better iodine status than did children who were currently breast-fed because breast milk contained low levels of iodine."
Selenium and iodine intakes and status in New Zealand and Australia.Thomson CD. Br J Nutr. 2004 May;91(5):661-72. Review. [abstract only]
"Most New Zealand soils contain relatively low concentrations of the anionic trace elements F, I and Se. Some areas of Australia also have a history of I deficiency. In view of current interest in establishing nutrient reference intakes for Se and I in New Zealand and Australia, it is timely to review current understanding of the intakes and status of these two elements. In spite of a recent increase in Se status, the status of New Zealanders remains low compared with populations of many other countries and may still be considered marginal, although the clinical consequences of the marginal Se status are unclear. There are no recent reports of blood Se levels in Australia, but earlier reports indicate that they were generally greater than those of New Zealanders. Similarly, the consequences of decreasing I status in Australia and New Zealand are unclear. Mild I deficiency in New Zealand has resulted in enlarged thyroid glands indicating an increased risk of goitre. Currently there is little evidence, however, of any associated clinical disease. Public health recommendations to reduce salt intake, together with the reduction in I content of dairy products, are likely to result in further decreases in the I status of New Zealand and Australian residents. Some action is needed to prevent this decline and it may be necessary to consider other means of fortification than iodized salt. The consequences of possible interactions between Se and I in human nutrition are also unclear and no practical recommendations can be made."
Assessment of requirements for selenium and adequacy of selenium status: a review.Thomson CD. Eur J Clin Nutr. 2004 Mar;58(3):391-402. Review. [abstract only]
"OBJECTIVE: The intent of this review is to evaluate the scientific evidence for the assessment of adequacy of selenium status and of the requirements for selenium. From this evidence, attempts have been made to define levels of plasma selenium and dietary selenium intake, which could be used for the assessment of deficiency or adequacy of selenium status. METHOD: The first section briefly reviews the methods for assessment of selenium status. The second section outlines the requirements for selenium based on a number of criteria, and how these have been translated into recommended intakes of selenium. In the final section, levels of plasma selenium and dietary intake based on different criteria of adequacy have been proposed. RESULTS AND CONCLUSION: The minimum requirement for selenium is that which prevents the deficiency disease, Keshan disease. The recommended intakes of selenium have been calculated from the requirement for optimum plasma glutathione peroxidase (GPx) activity that must, because of the hierarchy of selenoproteins, also take account of the amounts needed for normal levels of other biologically necessary selenium compounds. Whether optimal health depends upon maximization of GPx or other selenoproteins, however, has yet to be resolved, and the consequences of less-than-maximal GPx activities or mRNA levels need investigation. Intakes, higher than recommended intakes, and plasma selenium concentrations that might be protective for cancer or result in other additional health benefits have been proposed. There is an urgent need for more large-scale trials to assess any such beneficial effects and to provide further data on which to base more reliable estimates for intakes and plasma selenium levels that are protective."
Dietary and biochemical selenium status of urban 6- to 24-month-old South Island New Zealand children and their postpartum mothers.McLachlan SK, Thomson CD, Ferguson EL, McKenzie JE. J Nutr. 2004 Dec;134(12):3290-5.
"A community-based,
cross-sectional survey was conducted in the South Island of New
Zealand to assess the dietary and biochemical selenium status of
children (n = 136) and their mothers (n = 302), and to assess
factors influencing selenium status. Serum and plasma samples
from children and their mothers were analyzed for selenium using
graphite furnace atomic absorption spectrometry. Dietary selenium
intakes were analyzed from 3-d weighed diet records, and food
sources of selenium were quantified. Mean dietary selenium
intakes in infants (6-11.9 mo), toddlers (12-24 mo), and mothers
were below recommended levels. Toddlers had higher selenium
intakes than infants (13.7 +/- 8.4 and 7.9 +/- 6.2 microg/d,
respectively, P = 0.0001) and the selenium density of their diets
was also higher [3.2 +/- 1.7 and 2.4 +/- 1.7 microg/(MJ . d),
respectively, P = 0.003]. Household smoking was associated with
lower serum selenium concentrations in infants and toddlers (P =
0.02). South Island women who were currently pregnant had lower
plasma selenium concentrations (0.74 +/- 0.15 micromol/L) than
nonpregnant lactating and nonpregnant nonlactating women (0.94
+/- 0.16 and 0.93 +/- 0.16 micromol/L, respectively, P = 0.0001).
Clearly, pregnant women, infants and toddlers are at risk of
suboptimal selenium status, and further research is warranted to
assess potential effects in these groups. The finding of an
association between household smoking and lower selenium
concentrations in children should be investigated further.
Dietary interventions are recommended to improve dietary selenium
intakes in South Island children and their mothers."
Selenium and iodine intakes and status in New Zealand and Australia.Thomson CD. Br J Nutr. 2004 May;91(5):661-72. Review. [abstract only]
"Most New Zealand
soils contain relatively low concentrations of the anionic trace
elements F, I and Se. Some areas of Australia also have a history
of I deficiency. In view of current interest in establishing
nutrient reference intakes for Se and I in New Zealand and
Australia, it is timely to review current understanding of the
intakes and status of these two elements. In spite of a recent
increase in Se status, the status of New Zealanders remains low
compared with populations of many other countries and may still
be considered marginal, although the clinical consequences of the
marginal Se status are unclear. There are no recent reports of
blood Se levels in Australia, but earlier reports indicate that
they were generally greater than those of New Zealanders.
Similarly, the consequences of decreasing I status in Australia
and New Zealand are unclear. Mild I deficiency in New Zealand has
resulted in enlarged thyroid glands indicating an increased risk
of goitre. Currently there is little evidence, however, of any
associated clinical disease. Public health recommendations to
reduce salt intake, together with the reduction in I content of
dairy products, are likely to result in further decreases in the
I status of New Zealand and Australian residents. Some action is
needed to prevent this decline and it may be necessary to
consider other means of fortification than iodized salt. The
consequences of possible interactions between Se and I in human
nutrition are also unclear and no practical recommendations can
be made."
Serum selenium concentrations in New Zealand children.McLachlan SK, Thomson CD. Asia Pac J Clin Nutr. 2004;13(Suppl):S86. [abstract only]
"Background - The low
selenium content of New Zealand soils has resulted in sub-optimal
blood selenium concentrations in New Zealand residents. At
present there is no data on the biochemical selenium status of
New Zealand children. Objective - To determine the biochemical
selenium status of New Zealand children Design - The survey aimed
to recruit 3000 participants with 1000 children each of Maori,
Pacific, and New Zealand European and other (NZEO) ethnicity. The
nationally representative sample was recruited using a two-stage
process involving random selection of schools followed by random
selection of children within each school. Stored serum was
available from 1621 children, and selenium concentrations were
analysed using graphite furnace atomic absorption spectrometry.
Results - The mean (SEM) serum selenium level was 73.3 (1.5) (microg/L
(n=832) and 78.5 (1.6) (microg/L (n=789) in females and males,
respectively. Pacific Island children had the highest mean serum
selenium concentrations (81.6microg/L, n=667), followed by Maori
(76.0microg/L, n=468), and New Zealand European children (75.3 (microg/L,n=486).
Regional differences were found within New Zealand. Mean selenium
concentrations in South Island children ranged between 61.0 and
64.7microg/L compared with a range of 74.1 to 84.1microg/L in
North Island children (P<0.05). Conclusion - South Island
children have lower selenium concentrations compared with North
Island children. Dietary interventions to improve selenium status
in South Island children should be considered. The Ministry of
Health funded the selenium analysis and the 2002 National
Children's Nutrition Survey."
Selenium and iodine interactions with thyroid status.Thomson CD. Asia Pac J Clin Nutr. 2003;12 Suppl:S14. [abstract only]
"Background - The adequacy of selenium (Se) status may influence iodine metabolism because of Se's role in the deiodinase enzymes. Se deficiency may exacerbate symptoms of iodine deficiency. There is little research on any detrimental effects of marginal selenium intakes on thyroid status. Objective - This paper reports on two studies investigating (a) the relationship between Se status and thyroid status in a NZ population and (b) the effect of Se supplementation on TSH and the ratio of T(3)/T(4);. Design - Study 1: Plasma Se was determined in 199 Otago residents for which data was available on thyroid volume, plasma TSH, and plasma T(4). Study 2: TSH, T(4) and T(3) were measured in plasma from two supplementation studies: 57 smokers who received 100 microg Se or a placebo daily as selenomethionine; 172 subjects who received 200 microg daily as high-Se yeast (Precise) or a placebo. Outcomes - Study 1: In contrast to observations in France, preliminary analyses did not show significant associations between plasma Se and measures of thyroid status. Study2: Se supplementation resulted in a trend towards lower T(4) confirming an earlier study of a small but significant fall in T(4). Conclusions - Lack of association between plasma Se and thyroid status, and non-significant changes in T(4) suggest that Se status in NZ is adequate for optimal activity of the deiodinases."
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