Measurement of milk intake: tracer-to-infant deuterium dilution method

Deuterated driven new chemical entities: An optimistic way to improve therapeutic efficacy

In organic chemistry, the use of deuterium exchange as a tool to study the mechanism of chemical reaction has been well explored. Since two decades, the research focus on deuterated bioactive molecules has been gaining attention for investigating the therapeutic potential of deuterium replacement in a chemical structure. Recently, Food Drug Administration (FDA) approved the first deuterium-labeled drug "deutetrabenazine", and notified the deuterated drugs as new chemical entities (NCEs). Henceforth, the deuterium substitution driven structure activity relationship, preclinical pharmacokinetics, and toxicity studies were much initiated. Deuteration of a bioactive molecule often results in improved therapeutic efficacy due to the altered pharmacokinetic profile. This review provides a conceptual framework on the importance of deuterium atom in chemical structure of a drug, and its biological value in improved physiochemical properties, pharmacokinetics, biological target interaction, diagnosis, and toxicity. In addition, this review concisely updated the recent deuteration methods, chemical stability, challenges in drug development, deuterium-based imaging in diagnosis, and selected synthetic scheme of deuterated molecules.

The Volume of Breast Milk Intake in Infants and Young Children: A Systematic Review and Meta-Analysis

Objective: The objective of this study was to provide global breast milk intake estimates for infants and children from 0 to 3 years old. Materials and Methods: A systematic search of online databases (Embase, MEDLINE, and CENTRAL) was conducted and complemented with a manual search of additional databases (African Journals Online and LILACS), reference lists, and unpublished data. Studies with apparently healthy mothers and their children 0-3 years old worldwide were included. Random effects meta-analyses, subgroup analyses, and meta-regressions were conducted. Results: A total of 167 studies on breast milk intake were identified. The mean daily breast milk intake among all the studies included was 670 mL per day and 117 mL/kg per day. Breast milk intake was influenced by infant age, infant body weight, and breastfeeding practices. The deuterium dilution method tended to yield higher estimates than test-weighing methods. Breast milk intake over time was modeled with a nonlinear meta-regression: breast milk intake (mL/day) = 51-1.4 × days +180 × log(days). When restricting to studies involving healthy term infants exclusively breastfed up to 6 months, breast milk intake was 624 mL per day and 135 mL/kg per day at 1 month, 735 mL per day and 126 mL/kg per day at 3 months, 729 mL per day and 107 mL/kg per day at 6 months, and 593 mL per day and 61 mL/kg per day at 12 months. Conclusions: This review provides global breast milk intake estimates for infants and young children. It demonstrates differences in intakes according to region and measurement method, as well as longitudinal changes over the first year of life.

Maternal nutritional status and milk volume and composition in India: an observational study

BACKGROUND

Human milk provides essential nutrition for infants, and its benefits are well established. We lack data on the influence of maternal nutritional status on milk volume and composition in low-middle income countries.

OBJECTIVE

We aimed to 1) assess lactation performance (human milk volume, macronutrient composition, and infant energy intake) in Indian females and 2) examine the associations between maternal anthropometry (BMI, percentage body fat) and lactation performance.

METHODS

We conducted an observational study among 232 mother-infant dyads, 2 to 4 mo postpartum in Haryana, India. We used deuterium oxide dose-to-mother technique to measure milk volume and maternal percentage body fat and collected human milk samples to determine macronutrient and energy concentrations. Adjusted multiple linear regression models were used to examine the associations between maternal anthropometry and lactation performance.

RESULTS

The mean BMI and percentage body fat of mothers were 21.7 ± 3.6 kg/m² and 29.5 ± 7.7, respectively. Milk volume and macronutrient composition were similar to the reference values (means ± standard deviations: milk volume, 724 ± 184 mL/d; median (25th, 75th percentile); protein, 9.9 (8.3, 11.7) g/L; fat, 41.0 ± 15.2 g/L; energy density, 0.71 ± 0.14 kcal/g; lactose, 65.5 (55.3, 71.3) g/L). Maternal BMI and percentage body fat were not significantly associated with macronutrient composition. Both maternal BMI and percentage body fat were negatively associated with milk volume (-7.0, 95% CI: -12.4, -1.6 mL/d; -3.5, 95% CI: -6.0, -1.1mL/d, respectively) but there were no effects on the total energy intake of infants after adjusting for covariates.

CONCLUSION

Most mothers had a normal BMI and milk of similar composition and volume to reference values. Future work in populations with a greater burden of underweight and/or obesity are needed to examine the underlying mechanisms between maternal body composition and milk volume. This trial was registered at The Clinical Trials Registry- India as CTRI/2017/01/007636.

The importance of infants' lipid intake in human milk research

Human milk lipids are among the many nutrients delivered to the infant, providing >50% of the infant's calorie intake. These lipids are highly complex and variable, and bioactive, contributing to infant growth, development, and health. The lipid concentration of milk samples is often measured in human cohorts; however, few studies measure infant intake of milk. Intake is important because it considers the variability of both lipid concentration and infants' consumed volume of milk. Measurement of infants' lipid intake in exclusively breastfeeding infants requires 3 main considerations: human milk sampling protocol (ie, the collection of representative samples); measurement of the infant milk intake, because volume varies widely between infants; and appropriate analytical laboratory methods. The purpose of this review was to provide an overview of existing methodology and demonstrate the importance of measuring infants' lipid intake to understand the impact that human milk lipids have on infant outcomes.

Impact of Deuterium Substitution on the Pharmacokinetics of Pharmaceuticals

Objective: Stable heavy isotopes of hydrogen, carbon, and other elements have been incorporated into drug molecules, largely as tracers for quantitation during the drug development process. Studies involving the human use of drugs labeled with deuterium suggest that these compounds may offer some advantages when compared with their nondeuterated counterparts. Deuteration has gained attention because of its potential to affect the pharmacokinetic and metabolic profiles of drugs. Deutetrabenazine (Austedo, Teva Pharmaceutical Industries, Ltd) is the first deuterated drug to receive Food and Drug Administration approval. This deuterated form of the drug tetrabenazine is indicated for the treatment of chorea associated with Huntington’s disease as well as tardive dyskinesia. Ongoing clinical trials suggest that a number of other deuterated compounds are being evaluated for the treatment of human diseases and not merely as research tools. Data Sources: A search of the MEDLINE (1946 to present) database was undertaken using the Ovid interface. The search was conducted using the heading deuterium and then limited to Administration & Dosage, Adverse Effects, Pharmacokinetics, Pharmacology, Poisoning, Therapeutic Use, and Toxicity. Study Selection and Data Extraction: All articles were reviewed and those with human information were included. Review articles were likewise interrogated for additional published human data. Conclusions: Deuterated compounds may, in some cases, offer advantages over nondeuterated forms, often through alterations in clearance. Deuteration may also redirect metabolic pathways in directions that reduce toxicities. The approval of additional deuterated compounds may soon follow. Clinicians will need to be familiar with the dosing, efficacy, potential side effects, and unique metabolic profiles of these new entities.

Breastmilk Output in a Disadvantaged Community with High HIV Prevalence as Determined by the Deuterium Oxide Dose-to-Mother Technique

INTRODUCTION

World Health Organization breastfeeding guidelines for HIV-infected mothers are exclusive breastfeeding for 6 months and then continued breastfeeding for 12 months, provided the mother is receiving antiretroviral prophylaxis. Many African women perceive that breastmilk alone is not sufficient for their infant's nutritional requirements for the first 6 months of life, and mixed feeding is a common practice.

METHODOLOGY

A stable isotope technique was used to determine breastmilk output volumes and maternal body composition objectively at five different time points in the first year of the infant's life.

RESULTS

Breastmilk output volumes were high for HIV-infected mothers: 831 ± 185 g/day at 6 weeks; 899 ± 188 g/day at 3 months; 871 ± 293 g/day at 6 months; 679 ± 281 g/day at 9 months; and 755 ± 287 g/day at 12 months. These high output volumes had no negative impact on the mother's fat-free mass. The breastmilk output volumes for HIV-uninfected mothers were not significantly different to the outputs for HIV-infected mothers at any of the time points (p > 0.05): 948 ± 223 g/day at 6 weeks; 925 ± 227 g/day at 3 months; 902 ± 286 g/day at 6 months; 746 ± 263 g/day at 9 months; and 713 ± 264 g/day at 12 months.

CONCLUSION

This study using objective methodology shows that breastmilk outputs of HIV-infected mothers were relatively high (and within published reference ranges), and mothers are able to provide sufficient breastmilk for their infants without compromising their own fat-free mass.

The Deuterium Oxide-to-the-Mother Method Documents Adequate Breast-Milk Intake among Sri Lankan Infants

BACKGROUND

The WHO recommends that exclusive breastfeeding should last up to 6 mo. However, human milk intake of Sri Lankan infants has not been quantified scientifically.

OBJECTIVES

The objectives of this study were to measure the human milk intake of Sri Lankan infants during the first 6 mo of age and to document the breastfeeding practices of their mothers.

METHODS

Forty-eight healthy mother-infant dyads were randomly recruited for this cross-sectional study at well-baby clinics. Milk intake was measured using the deuterium oxide-to-the-mother technique over a period of 2 wk. Information on breastfeeding practice and living standards of the participants were gathered using an interviewer-administered questionnaire.

RESULTS

Human milk intake was 672 ± 123 g ⋅ d(-1) (mean ± SD), 776 ± 212 g ⋅ d(-1), and 801 ± 51 g ⋅ d(-1) for infants <2 mo, 2 to <4 mo, and 4-6 mo of age, respectively. The milk intakes were not different among the age groups. Maternal body composition, age, or parity had no effects on milk intake of the infants. However, mother's education : P < 0.05, r = 0.35), infant's age (P < 0.05, r = 0.30), and body mass index (P < 0.05, r = 0.41 : positively correlated with the milk intake. Over 63% of mothers had commenced breastfeeding within 30 min of delivery. About 60% of the mothers were feeding the baby 6-10 times during the daytime and >81% intended to continue exclusive breastfeeding until 6 mo of age.

CONCLUSION

This study, for the first time, documented the adequacy of breast-milk intake among Sri Lankan infants and the nutrition status of the mothers.

Methodological approaches for dietary intake assessment in formula-fed infants

BACKGROUND AND OBJECTIVE

The estimation of dietary intake remains a challenge in human nutritional studies. In infants, the use of food diaries (FDs) is a suitable method already validated; however, this method is not exempt from error. In formula-fed infants, dilution of powdered formulas may produce errors. Our aim was to develop and validate standard operating procedures (SOPs) for the assessment of dietary intake in formula-fed infants, attending potential sources of error.

METHODS

We analysed sources of error in a random subsample of 3-day FDs from 100 infants enrolled in the European Childhood Obesity Project. Calculations to estimate intakes were standardised and included in a software tool (SOPsystem). An evaluation of a simulated FD was performed by 9 trained nutritionists and 23 nutrition students (n=225 and n=575 bottle evaluations, respectively) to compare the results obtained when using or not the SOPsystem. Correct answers (%), coefficients of variation, and the time spent (minutes) to assess the simulated FD were analysed.

RESULTS

Overall, 60% of the FDs contained reports of incorrect volumes, and 37% reported incorrect formula dilutions. When the SOPsystem was used, correct answers in the simulated FD were more frequent (P<0.001) and the mean coefficient of variation and the time spent were lower (P<0.005 and P<0.01, respectively).

CONCLUSIONS

The development and implementation of SOPs with a software tool that identifies specific sources of error in record-keeping achieved a harmonised and improved process for assessing dietary intakes in formula-fed infants, minimising errors in calculations and reducing the work time invested.

Field and laboratory methods in human milk research

Human milk is a complex and variable fluid of increasing interest to human biologists who study nutrition and health. The collection and analysis of human milk poses many practical and ethical challenges to field workers, who must balance both appropriate methodology with the needs of participating mothers and infants and logistical challenges to collection and analysis. In this review, we address various collection methods, volume measurements, and ethical considerations and make recommendations for field researchers. We also review frequently used methods for the analysis of fat, protein, sugars/lactose, and specific biomarkers in human milk. Finally, we address new technologies in human milk research, the MIRIS Human Milk Analyzer and dried milk spots, which will improve the ability of human biologists and anthropologists to study human milk in field settings.

Is the macronutrient intake of formula-fed infants greater than breast-fed infants in early infancy?

Faster weight gain early in infancy may contribute to a greater risk of later obesity in formula-fed compared to breast-fed infants. One potential explanation for the difference in weight gain is higher macronutrient intake in formula-fed infants during the first weeks of life. A systematic review was conducted using Medline to assess the macronutrient and energy content plus volume of intake in breast-fed and formula-fed infants in early infancy. All studies from healthy, term, singleton infants reporting values for the composition of breast milk during the first month of life were included. The energy content of colostrum (mean, SEM: 53.6 ± 2.5 kcal/100 mL), transitional milk (57.7 ± 4.2 kcal/100 mL), and mature milk (65.2 ± 1.1 kcal/100 mL) was lower than conventional infant formula (67 kcal/100 mL) on all days analyzed. The protein concentration of colostrum (2.5 ± 0.2 g/100 mL) and transitional milk (1.7 ± 0.1 g/100 mL) was higher than formula (1.4 g/100 mL), while the protein content of mature milk (1.3 ± 0.1 g/100 mL) was slightly lower. Formula-fed infants consume a higher volume and more energy dense milk in early life leading to faster growth which could potentially program a greater risk of long-term obesity.

Adequacy of milk intake during exclusive breastfeeding: a longitudinal study

OBJECTIVE

To test whether and how human lactation and breastfeeding practices can adapt to fulfill infant energy requirements during exclusive breastfeeding for 6 months.

METHODS

The First-Feed study was a longitudinal, observational field study to measure milk intake, energy intake (from the doubly labeled water method), anthropometry, and breastfeeding practices at 2 time points around 15 and 25 weeks of age. Fifty healthy exclusively breastfeeding mother-infant dyads were included from breastfeeding support groups in greater Glasgow, Scotland. Forty-seven completed (23 boys), and 41 were exclusively breastfed to 25 weeks of age.

RESULTS

Milk intakes were higher than literature values (923 [SD: 122] g/day, n = 36; and 999 [SD: 146] g/day, n = 33) at both 15 and 25 weeks of age (both P < .001) and increased significantly between time points (mean increase: 61 g/day [95% confidence interval: 23-99]; P = .003). Infant growth was normal compared with World Health Organization Child Growth Standards, and energy intakes were adequate compared with references for energy requirements. Behavioral data indicated no evidence of strain on breastfeeding practices.

CONCLUSIONS

Results of this prospective study reveal that when mothers are well supported and follow the World Health Organization recommendation on breastfeeding, milk intakes are high and increase over time, and there is adequate energy intake, normal infant growth, and no marked changes in breastfeeding practices. This new empirical evidence on adaptations during exclusive breastfeeding should help health professionals promote the initiation, duration, and exclusivity of breastfeeding.

2H2O turnover method as a means to detect bias in estimations of intake of nonbreast milk liquids in breast-fed infants

OBJECTIVE

Firstly, to compare food, and macronutrient intake as obtained from a single 24-h recall and a frequency questionnaire (FQ) covering a 14-day period in breast-fed infants aged 4 months of age. Secondly, nonbreast milk water intake (NB-WI, ml/day) was used as an estimation of energy and macronutrient intake, and NB-WI as calculated from FQ (NB-WIFQ) was compared with NB-WI as measured using the dose-to-the-mother 2H2O turnover method (NB-WIDO) covering the same 14-day period.

DESIGN

Cross-sectional.

SETTING

Community-based study in urban Pelotas, Southern Brazil.

SUBJECTS

In all, 67 breast-fed infants aged 4 months of age recruited at birth.

MAIN OUTCOME MEASURES

(1) Bias in estimations of food and macronutrient intake of the 24-h recall relative to FQ; (2) Bias in NB-WIFQ relative to NB-WIDO.

RESULTS

In infants with an energy intakeFQ from complementary foods above the 50th percentile (1.03 kcal/day), estimations of water, tea, juice, and milk intake were not different between 24-h recall and FQ (n=34). Nor were estimations of energy and macronutrient intake (protein, fat, and carbohydrates) different between the two methods, and bias was nonsignificant. NB-WIDO was divided into quintiles and compared with NB-WI(FQ). The first two quintiles included negative values for NB-WIDO as a result of random errors of the 2H2O turnover method. Subsequently, bias of NB-WIFQ relative to NB-WIDO was positive in the 1st (P=0.001) and 2nd quintile (P=0.638), respectively. Bias was negative for the three highest quintiles, and within this group, underestimation by FQ was significant for the 3rd and 4th quintile (-57.4%, P=0.019; -43.7%, P=0.019).

CONCLUSIONS

Firstly, at the age of 4 months FQ covering a 14-day period provides similar results on food and macronutrient intake as compared to a single 24-h recall for estimations of complementary liquid foods. Secondly, NB-WIFQ appeared to be a good proxy for macronutrient and energy intake in breast-fed infants receiving other liquids. In infants with NB-WIDO>0, the method provides a useful tool for the detection of bias from FQ, and results indicate an underestimation from FQ relative to the 2H2O turnover method. This exercise could be applied wherever the 2H2O turnover method is used in combination with conventional food consumption techniques for measuring intake of nonbreast milk liquids of breast-fed infants in whom solid foods have not yet been introduced. It would help interpreting estimations of macronutrient intake, and could be relevant to studies of dietary intake of infants and its relationship with growth and health.

Limits to sustained energy intake VII. Milk energy output in laboratory mice at thermoneutrality

The limits to sustained energy intake at peak lactation could be imposed peripherally, by the capacity of the mammary glands, or centrally, by the capacity of the animal to dissipate body heat generated as a by-product of processing food and producing milk. To distinguish between the two hypotheses,we examined milk energy output at peak lactation in MF1 laboratory mice exposed to 30°C (N=12), 21°C (N=10; published data)and 8°C (N=10; published data). The peripheral limitation hypothesis predicts that milk energy output will remain constant at different temperatures, while the heat dissipation limit hypothesis predicts a decline in milk energy output as temperature increases. Since estimates of milk energy output in small mammals can vary depending on the calculation method used, we evaluated the milk energy output of mice (N=24) using four different methods: (1) as the difference between metabolizable energy intake and daily energy expenditure of the female, (2) from female water turnover, (3) from pup water turnover and (4) from the energy budget of the litter. We assessed these four methods by comparing their accuracy, precision and sensitivity to changes in parameters involved in the calculations. Methods 1, 3 and 4 produced similar estimates of milk energy output, while those derived from female water turnover were significantly lower and more variable. On average, mice at 30°C exported significantly less energy as milk (87.7 kJ day–1) than mice at 21°C (166.7 kJ day–1) and 8°C (288.0 kJ day–1). This reduction in milk energy output at 30°C was caused by a significant decline in both milk flow (20.0 g day–1, 12.9 g day–1 and 8.5 g day–1 at 8°C, 21°C and 30°C, respectively) and gross energy content of milk (14.6 kJ g–1, 13.1 kJ g–1 and 10.5 kJ g–1 at 8°C, 21°C and 30°C, respectively). Milk produced at 30°C contained significantly less total solids (34.4%) than milk at 21°C (40.9%) and 8°C (41.5%) and significantly less fat(20.0%) than milk at 21°C (26.4%) and 8°C (30.3%). The reduced milk energy output in mice exposed to 30°C, paralleled by their reduced food intake and low reproductive output, argues against the peripheral limitation hypothesis and provides strong support for the heat dissipation limit hypothesis.

Is suckling behaviour a useful predictor of milk intake? A review

In studies on mammalian parental investment, time spent suckling is often used as a predictor of the milk transferred from mother to infant. It is assumed that the rate of milk transfer is positively correlated with the time spent suckling. However, this assumption has not been tested and empirical studies show conflicting results. Nevertheless, in species in which suckling can readily be observed, time spent suckling is still used to measure milk transfer, although an increasing number of workers recognize that the measure is potentially inaccurate. A meta-analysis on studies that have correlated measures of time spent suckling with milk intake estimates based on weight gain revealed a weak positive relationship and significant heterogeneity between studies. Isotope-labelling techniques for the measurement of milk transfer independent of behaviour have been in use since the 1970s, particularly in studies of species in which suckling is difficult to observe. Only one study has attempted to correlate behavioural measures with independent isotope measures, and it found no relationship between the two measures. I suggest that researchers have avoided such a test as it is unlikely that a strong relationship will be found between milk transfer and suckling behaviour, and I discuss the various factors that confound the relationship and contribute to high heterogeneity between studies. Consequently, the assumption that milk transfer can be measured by time spent suckling has inadequate empirical foundation, and needs to be tested using isotope-labelling methods. Copyright 1998 The Association for the Study of Animal Behaviour

Physical fitness influences water turnover and body water changes during trekking

PURPOSE

This study was performed to assess water turnover and changes of body water during a trekking tour at moderate altitude.

METHODS

Fifteen healthy normally trained adults participated in a 7-d backpack trek tour in the Swiss Alps (total walking distance: 120.5 km; cumulated altitude difference: 6990 m (uphill) and 7550 m downhill; lowest point: 1285 m; highest point: 3317 m). Total body water and water turnover were measured using deuterium dilution and elimination (oral load of 0.33 g 99.8% D2O per kg body weight, overnight equilibration period, pre- and postdose saliva samples immediately before and after sleep, analysis of D2O concentrations in saliva using Fourier-transform infrared spectroscopy, CV < 1%). Physical training state was assessed after the tour using the lactate-exercise intensity relationship obtained by performing 50-W increments every 3 min on a cycle ergometer.

RESULTS

Body water decreased from the evening of day 0 to the evening of day 4 (from 45.3 +/- 7.3 L to 43.4 +/- 7.6 L, P < 0.05), and did not significantly decrease (43.5 +/- 7.9 L) until the evening of day 5 (maximum of trekking exercise intensity). Mean daily water turnover was 5.7 +/- 1.8 L x d(-1) corresponding to 78.7 +/- 17.5 mL x kg(-1) x d(-1). Body water changes and water turnover were significantly related to the exercise intensity obtained at the lactate threshold as well as at the level of 4 mM lactate.

CONCLUSIONS

This correlation may be in part explained by differing glycogen content of muscle tissue.

Correction for environmental water influx in measurement of milk volume intake by deuterium turnover in infants

Measurement of milk volume intake (MVI) in infants is a useful tool for assessing nutritional intake. Current measurement techniques include test-weighting, weighting formula-bottles, and calculation of MVI from water turnover estimated isotopically. Test-weighing of breast-fed infants may disturb normal feeding behaviour and thus influence intake. Calculation of MVI from water turnover is a non-invasive measurement method and can be applied to all infants whether breast-fed or formula-fed. The method requires correction for environmental water influx (EWI) which constitutes non-oral water intake. EWI has previously been investigated only in premature or malnourished infants. The correction factor for EWI was calculated by comparing MVI obtained from weighing formula-bottles and measured isotopically in 21 formula-fed infants at 12 weeks of age. The mean correction factor, by which total water intake should be adjusted to obtain oral water intake, was 0.937 (S.E. 0.017). The proportion of water intake derived from non-oral sources was therefore 6.3%.

The benefits of probabilistic exposure assessment: three case studies involving contaminated air, water, and soil

Probabilistic risk assessments are enjoying increasing popularity as a tool to characterize the health hazards associated with exposure to chemicals in the environment. Because probabilistic analyses provide much more information to the risk manager than standard "point" risk estimates, this approach has generally been heralded as one which could significantly improve the conduct of health risk assessments. The primary obstacles to replacing point estimates with probabilistic techniques include a general lack of familiarity with the approach and a lack of regulatory policy and guidance. This paper discusses some of the advantages and disadvantages of the point estimate vs. probabilistic approach. Three case studies are presented which contrast and compare the results of each. The first addresses the risks associated with household exposure to volatile chemicals in tapwater. The second evaluates airborne dioxin emissions which can enter the food-chain. The third illustrates how to derive health-based cleanup levels for dioxin in soil. It is shown that, based on the results of Monte Carlo analyses of probability density functions (PDFs), the point estimate approach required by most regulatory agencies will nearly always overpredict the risk for the 95th percentile person by a factor of up to 5. When the assessment requires consideration of 10 or more exposure variables, the point estimate approach will often predict risks representative of the 99.9th percentile person rather than the 50th or 95th percentile person. This paper recommends a number of data distributions for various exposure variables that we believe are now sufficiently well understood to be used with confidence in most exposure assessments. A list of exposure variables that may require additional research before adequate data distributions can be developed are also discussed.

Measurement of nutrient intake by deuterium dilution in premature infants

To assess whether a simple nonrestrictive method of determining nutrient intake could be applied to premature infants, we compared actual measured formula intake during a 7-day period with intake calculated from deuterium dilution in 13 hospitalized, growing, premature newborn infants. An oral dose of deuterium oxide (D2O) was administered, and urine samples were analyzed by deuterium nuclear magnetic resonance spectrometry for D2O concentration. Using an exponential model, we calculated formula intake from the decline in D2O concentration during the 7-day study period. Intake as assessed by the deuterium model correlated well with actual intake (r = 0.93; p < 0.001). However, because the deuterium dilution model measures both dietary and nondietary water intake (metabolic and cutaneous water influx), deuterium dilution-derived intake exceeded actual intake by 25 +/- 18 ml/kg per day (16% +/- 11%). When corrections were applied to account for nondietary water intake, deuterium dilution-derived nutrient intake (160 +/- 30 ml/kg per day) closely approximated actual intake (155 +/- 17 ml/kg per day). If corrections are made for nondietary water intake, the deuterium dilution method may be a useful nonrestrictive method of measuring nutrient intake in a variety of neonatal populations.

Water turnover of healthy children measured by deuterated water elimination

For healthy children up to 15 years of age, no data exist regarding water turnover as directly measured using stable isotope techniques. Water turnover was measured in 171 healthy children (88 girls, 83 boys, age: 6 weeks-15 years) whilst living in their normal environment. Water turnover was calculated from the equilibrium of 2H2O concentration reached in the urine 2-3 h after an oral test load of 2 ml 2H2O/kg and the subsequent elimination rate of 2H2O. Daily water turnover decreased from 160 ml/kg (3 months), 100 ml/kg (12 months), 65 ml/kg (3 years) to 40 ml/kg at 15 years of age. Fluid intake was then calculated by subtracting the estimated metabolic water production from water turnover and this data was compared with recommended values. Our calculation of spontaneous daily fluid intake for these healthy children is within the recommended range during the 1st year of life, whereas for older children the recommendations exceed the spontaneous intake by a factor of 1.2-2.

Measurement of water turnover using a stable isotope technique: calculation of error propagation

Water turnover may be determined with stable isotope techniques from the product of tracer dilution space and tracer elimination rate. Tracer concentrations must be measured in two body fluid samples which are separated by a sampling interval. The tracer concentration of the first sample may be charged with an error which may be due to analytical errors, incomplete tracer dilution or because the necessary steady-state assumption (water influx equals water efflux) is violated at the moment of tracer loading. Error propagation shows that the influence of this error on the estimation of water turnover is partially compensated for. The goodness of compensation depends on the sampling interval and on the magnitude of the error of the first sample. The error is best compensated using sampling intervals of 1.5 tracer half life.