Papers by Alida Melse-Boonstra
Background: Serum retinol concentration determined by high-performance liquid chromatography (HPL... more Background: Serum retinol concentration determined by high-performance liquid chromatography (HPLC) is
recommended by the World Health Organization to assess population vitamin A status. This assay is expensive,
technically demanding and rarely available in developing countries. Our objective was a) to assess the diagnostic
performance of proxy markers in detecting vitamin A deficiency and b) to derive decision rules based on these
markers to estimate vitamin A deficiency prevalence.
Methods: A survey was conducted in 15 rural primary schools in Eastern Province, Kenya, with 375 children aged
6 to 12 years (25 randomly selected per school). Serum retinol concentration <0.70 μmol/L by HPLC was used to
define vitamin A deficiency. Proxy markers for vitamin A deficiency were serum concentrations of retinol binding
protein (RBP), transthyretin, retinol measured by fluorometry and RBP:transthyretin molar ratio.
Results: The prevalence of vitamin A deficiency (HPLC) was 18%. Transthyretin and RBP showed the best diagnostic
performance individually, with area-under-the-curve (AUC) values of 0.96 and 0.93. When combined, and with C-reactive
protein added, the AUC increased to 0.98. A simple decision rule {(−15.277 × [RBP, μmol/L] - 7.013 × [Transthyretin,
μmol/L] + 0.367 × [C-reactive protein, mg/L] + 24.714) > 0.496} yielded prevalence estimates of vitamin A deficiency
that is unbiased by diagnostic error.
Conclusions: The combination of transthyretin, RBP and C-reactive protein concentrations could eventually replace
retinol concentration by
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Analytical Chemistry, 2001
Folic acid is an essential nutrient, and folate deficiency is associated with a variety of disord... more Folic acid is an essential nutrient, and folate deficiency is associated with a variety of disorders including neural tube defects (during pregnancy) and heart disease. A fast, sensitive, and robust HPLC-tandem mass spectrometry (LC-MS-MS) method was developed for the quantification of free folic acid, tetrahydrofolate, 5'-methyltetrahydrofolate, and 5'-formyltetrahydrofolate in human plasma. Sample preparation required only acetonitrile precipitation of proteins followed
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The American journal of clinical nutrition, 2006
The bioavailability of dietary folate may be hampered by the need of the glutamate moieties to be... more The bioavailability of dietary folate may be hampered by the need of the glutamate moieties to be deconjugated before absorption. Previous studies comparing the bioavailabilities of polyglutamyl and monoglutamyl folic acid had inconsistent results. The objective was to estimate the bioavailability of polyglutamyl relative to that of monoglutamyl folic acid by using a sensitive stable-isotope approach that allowed for the administration of multiple low doses in humans. Twenty subjects aged 20-50 y ingested 2 capsules daily for 28 d; each capsule contained approximately 50 nmol [(13)C(6)]hexaglutamyl and approximately 50 nmol [(13)C(11)]monoglutamyl folic acid. Amounts of the isotopically labeled compounds in the capsules were verified by various methods. The degrees of isotopic enrichment of plasma 5-methyltetrahydrofolate with (13)C(6) and (13)C(11) were measured by using liquid chromatography tandem mass spectrometry, and the ratio of (13)C(6) to (13)C(11) ((13)C(6):(13)C(11)) in p...
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BMC Medicine, 2015
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Thyroid, 2009
Chronic iodine deficiency (ID) increases thyrotropin (TSH) concentrations and produces a thyroid ... more Chronic iodine deficiency (ID) increases thyrotropin (TSH) concentrations and produces a thyroid hormone pattern consistent with subclinical hypothyroidism (ScH). ScH may be associated with cardiovascular disease risk factors. Thus, the study aim was to determine if iodine treatment of children with elevated TSH concentrations due to ID would affect their lipid profile, insulin (C-peptide) levels, and/or subclinical inflammation. In controlled intervention trials of oral iodized oil or iodized salt, 5-14-year-old children from Morocco, Albania, and South Africa with TSH concentrations &amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;gt; or = 2.5 mU/L (n = 262) received 400 mg iodine as oral iodized oil or household distribution of iodized salt containing 25 microg iodine/g salt. At baseline and after 5 or 6 months, urinary iodine (UI) and blood concentrations of total thyroxine, TSH, C-reactive protein (CRP), C-peptide, and lipids were measured. Median (range) UI at baseline was 46 (2-601) microg/L. Compared to the control group, iodine treatment significantly increased UI and total thyroxine and decreased TSH, C-peptide, and total and low-density lipoprotein cholesterol. The mean low-density lipoprotein/high-density lipoprotein cholesterol ratio fell from 3.3 to 2.4 after iodine treatment (p &amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;lt; 0.001). Iodine treatment had no significant effect on concentrations of high-density lipoprotein cholesterol, triglycerides, or C-reactive protein. Correction of ID-associated ScH improves the insulin and lipid profile and may thereby reduce risk for cardiovascular disease. This previously unrecognized benefit of iodine prophylaxis may be important because ID remains common in rapidly developing countries with increasing rates of obesity and cardiovascular disease.
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Journal of Nutrition, 2009
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British Journal of Nutrition, 2008
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British Journal of Nutrition, 2011
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British Journal of Nutrition, 2003
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Public Health Nutrition, 2014
To compare the iodine status of pregnant women and their children who were sharing all meals in B... more To compare the iodine status of pregnant women and their children who were sharing all meals in Bangalore, India. A cross-sectional study evaluating demographic characteristics, household salt iodine concentration and salt usage patterns, urinary iodine concentrations (UIC) in women and children, and maternal thyroid volume (ultrasound). Antenatal clinic of an urban tertiary-care hospital, which serves a low-income population. Healthy pregnant women in all trimesters, aged 18-35 years, who had healthy children aged 3-15 years. Median (range) iodine concentrations of household powdered and crystal salt were 55·9 (17·2-65·9) ppm and 18·9 (2·2-68·2) ppm, respectively. The contribution of iodine-containing supplements and multi-micronutrient powders to iodine intake in the families was negligible. Adequately iodized salt, together with small amounts of iodine in local foods, were providing adequate iodine during pregnancy: (i) the overall median (range) UIC in women was 172 (5-1024) µg/l; (ii) the median UIC was &amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;amp;gt;150 µg/l in all trimesters; and (iii) thyroid size was not significantly different across trimesters. At the same time, the median (range) UIC in children was 220 (10-782) µg/l, indicating more-than-adequate iodine intake at this age. Median UIC was significantly higher in children than in their mothers (P=0·008). In this selected urban population of southern India, the iodized salt programme provides adequate iodine to women throughout pregnancy, at the expense of higher iodine intake in their children. Thus we suggest that the current cut-off for median UIC in children indicating more-than-adequate intake, recommended by the WHO/UNICEF/International Council for the Control of Iodine Deficiency Disorders may, need to be reconsidered.
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Nutrition Journal, 2013
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Nutrients, 2012
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Journal of Trace Elements in Medicine and Biology, 2012
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Analytical Chemistry, 2001
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American Journal of Clinical Nutrition, 2011
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Food & Nutrition Research, 2015
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Papers by Alida Melse-Boonstra
recommended by the World Health Organization to assess population vitamin A status. This assay is expensive,
technically demanding and rarely available in developing countries. Our objective was a) to assess the diagnostic
performance of proxy markers in detecting vitamin A deficiency and b) to derive decision rules based on these
markers to estimate vitamin A deficiency prevalence.
Methods: A survey was conducted in 15 rural primary schools in Eastern Province, Kenya, with 375 children aged
6 to 12 years (25 randomly selected per school). Serum retinol concentration <0.70 μmol/L by HPLC was used to
define vitamin A deficiency. Proxy markers for vitamin A deficiency were serum concentrations of retinol binding
protein (RBP), transthyretin, retinol measured by fluorometry and RBP:transthyretin molar ratio.
Results: The prevalence of vitamin A deficiency (HPLC) was 18%. Transthyretin and RBP showed the best diagnostic
performance individually, with area-under-the-curve (AUC) values of 0.96 and 0.93. When combined, and with C-reactive
protein added, the AUC increased to 0.98. A simple decision rule {(−15.277 × [RBP, μmol/L] - 7.013 × [Transthyretin,
μmol/L] + 0.367 × [C-reactive protein, mg/L] + 24.714) > 0.496} yielded prevalence estimates of vitamin A deficiency
that is unbiased by diagnostic error.
Conclusions: The combination of transthyretin, RBP and C-reactive protein concentrations could eventually replace
retinol concentration by
recommended by the World Health Organization to assess population vitamin A status. This assay is expensive,
technically demanding and rarely available in developing countries. Our objective was a) to assess the diagnostic
performance of proxy markers in detecting vitamin A deficiency and b) to derive decision rules based on these
markers to estimate vitamin A deficiency prevalence.
Methods: A survey was conducted in 15 rural primary schools in Eastern Province, Kenya, with 375 children aged
6 to 12 years (25 randomly selected per school). Serum retinol concentration <0.70 μmol/L by HPLC was used to
define vitamin A deficiency. Proxy markers for vitamin A deficiency were serum concentrations of retinol binding
protein (RBP), transthyretin, retinol measured by fluorometry and RBP:transthyretin molar ratio.
Results: The prevalence of vitamin A deficiency (HPLC) was 18%. Transthyretin and RBP showed the best diagnostic
performance individually, with area-under-the-curve (AUC) values of 0.96 and 0.93. When combined, and with C-reactive
protein added, the AUC increased to 0.98. A simple decision rule {(−15.277 × [RBP, μmol/L] - 7.013 × [Transthyretin,
μmol/L] + 0.367 × [C-reactive protein, mg/L] + 24.714) > 0.496} yielded prevalence estimates of vitamin A deficiency
that is unbiased by diagnostic error.
Conclusions: The combination of transthyretin, RBP and C-reactive protein concentrations could eventually replace
retinol concentration by