Proxy markers of serum retinol concentration, used alone and in combination, to assess population vitamin A status in Kenyan children: a cross-sectional study

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 HPLC in resource-poor settings as the preferred method to assess the population burden of vitamin A deficiency.

Evaluation of using spot urine to replace 24 h urine sodium and potassium excretions

OBJECTIVE

The most accurate method to estimate Na and K intakes is to determine 24 h urinary excretions of these minerals. However, collecting 24 h urine is burdensome. Therefore it was studied whether spot urine could be used to replace 24 h urine samples.

DESIGN

Participants collected 24 h urine and kept one voiding sample separate. Na, K and creatinine concentrations were analysed in both 24 h and spot urine samples. Also 24 h excretions of Na and K were predicted from spot urine concentrations using the Tanaka and Danish methods.

SETTING

In 2011 and 2012, urine samples were collected and brought to the study centre at Wageningen University, the Netherlands.

SUBJECTS

Women (n 147) aged 19-26 years.

RESULTS

According to p-aminobenzoic acid excretions, 127 urine collections were complete. Correlations of Na:creatinine, K:creatinine and Na:K between spot urine and 24 h urine were 0·68, 0·57 and 0·64, respectively. Mean 24 h Na excretion predicted with the Tanaka method was higher (difference 21·2 mmol/d, P<0·001) than the measured excretion of 131·6 mmol/d and mean 24 h Na excretion predicted with the Danish method was similar (difference 3·2 mmol/d, P=0·417) to the measured excretion. The mean 24 h K excretion predicted with the Tanaka method was higher (difference 13·6 mmol/d, P<0·001) than the measured excretion of 66·8 mmol/d. Bland-Altman plots showed large individual differences between predicted and measured 24 h Na and K excretions.

CONCLUSIONS

The ratios of Na:creatinine and K:creatinine in spot urine were reasonably well associated with their respective ratios in 24 h urine and appear to predict mean 24 h Na excretion of these young, Caucasian women.

[Dietary trans-fatty acids: a risk factor for coronary disease]

Unsaturated fatty acids with their double bond in trans configuration raise serum low-density lipoprotein (LDL) cholesterol and lipoprotein(a) levels, and lower high-density lipoprotein (HDL) cholesterol in humans when substituted for cis unsaturated fatty acids in the diet. These effects should increase the risk of coronary heart disease, which is confirmed by epidemiological studies. Trans fatty acids are formed from cis unsaturated fatty acids during hydrogenation of vegetable oils in food industries. Until recently, major dietary sources of trans fatty acids in the Netherlands were frying fats, shortenings, and margarines, which in the past contained up to 50% of trans fatty acids. Nowadays, most shortenings and margarines sold in the Netherlands have a low trans fatty acid content due to manufacturing changes in the recent past. However, frying fats used in fast-food outlets still contain over 30% of trans fatty acids. French fries sold in these outlets provide 7-8 g of trans fatty acids per portion. Producers of frying fats for fast-food outlets therefore should also reduce the trans fatty acid content of their products as much as possible.

Validity of food intake measurement of adult Turkish immigrants in The Netherlands

OBJECTIVE

To study the validity of the reported food intake in a study which was designed to assess exposure to dioxins from food sources.

DESIGN

Repeated diet recalls were used to collect food intake data within a period of four months. Data on energy intake were related to computed basal metabolic rate (BMR).

SETTING AND SUBJECTS

A group of 69 Turkish immigrants (30 men and 39 women aged 18-59 years) from two municipalities in the Eastern part of the Netherlands, whose selected basic socio-demographic characteristics reflect those of adult Turkish living in the Netherlands.

RESULTS AND CONCLUSIONS

A mean energy intake (EI) to BMR ratio of 1.32 for women (mean EI = 8.1 MJ/day) and 1.36 for men (mean EI = 10.6 MJ/day) was found. Subjects in the lower and upper tertile of EI/BMR ratio differed only in body mass index (BMI: kg/m2). Pearson's correlation coefficient between EI/BMR and BMI was -0.39 (P < 0.05). The observed high prevalence of obesity in adult Turkish people complicates, as in other cultures, an accurate assessment of food intake.