Day-to-day and within-day variation in urinary iodine excretion.

OBJECTIVE: To examine the day-to-day and within-day variation in urinary iodine excretion and the day-to-day variation in iodine intake. DESIGN: Collection of consecutive 24-h urine samples and casual urine samples over 24h. SETTING: The study population consisted of highly motivated subjects from our Institute. SUBJECTS: Study 1: Ten healthy subjects (seven females and three males) aged 30-46 y. Study 2: Twenty-two healthy subjects (9 males and 13 females) aged 30-55 y. METHODS: Study 1: 24-h urine samples were collected for four consecutive days. Study 2: Each urine voided over 24 h was collected into separate containers. In both studies dietary records were kept. MAIN OUTCOME MEASURES: Twenty-four-hour urinary iodine excretion, 24-h urinary iodine excretion estimated as I/Cr*24 h Cr and as a concentration in casual urine samples. RESULTS: Study 1: Both iodine excreted in 24-h urine and iodine intake varied from day-to-day. Iodine excretion correlated with iodine intake (=-0.46, P=0.01). Iodine intake (mean 89 +/- 6.5 microg/d) was not significantly different from iodine excretion (mean 95 +/- 5.3 microg/d). Study 2: Twenty-four hour iodine excretion estimated as I/Cr*24 h Cr from the morning urine sample was significantly lower than actual 24-h iodine excretion, whereas 24-h iodine excretion estimated as I/Cr*24 h Cr from the first sample after the morning sample and the last sample before the subjects went to bed was not significantly different from actual 24-h iodine excretion. Twenty-four-hour urine excretion estimated as a concentration was lower than actual 24-h iodine excretion in casual urine taken at any time of the day. CONCLUSIONS: For determination of iodine status in an individual, more than one 24-h urine sample must be used. The use of the I/Cr ratio in casual urine samples is a usable measure of iodine status if corrected for the age- and sex-adjusted 24-h creatinine excretion. Further, the study suggests that fasting morning urine samples would underestimate iodine status in this population.     

Iodine content of human milk and dietary iodine intake of Korean lactating mothers

Korea's food culture includes the consumption of seaweed, which is abundant and has a high iodine content. Because it is customary to serve seaweed soup to new mothers, the consumption of seaweed increases dramatically when a woman is lactating. The present study was undertaken for the purpose of determining the iodine content in human milk of Korean lactating mothers according to dietary iodine intake. The iodine content of human milk and dietary iodine intake from 50 lactating mothers were analyzed at 2 to 5 days and at 4 weeks postpartum. The dietary iodine intake was assessed by the 24-hour recall method. The iodine content in human milk was analyzed by neutron activation analysis (NAA). The average daily iodine intake of lactating mothers was 2744 micrograms at 2 to 5 days postpartum, decreasing significantly to 1295 micrograms at 4 weeks postpartum. The major sources of iodine were seaweed (87%) and cows' milk (7%). The average iodine content in colostrum and mature milk was 2170 micrograms/l and 892 micrograms/l, respectively. There was a significant reduction in the levels of iodine in human milk depending on the lactation period. A significant correlation between maternal iodine intake and iodine content of human milk was observed (P < 0.0001). The frequency of seaweed soup intake in lactating mothers seems to be a modifying factor in the iodine intake level and the iodine content in human milk. The level of dietary iodine intake and the iodine content of breast milk of Korean lactating mothers is found to be much higher than in other countries.     

Electrolyte loss in sweat and iodine deficiency in a hot environment

The authors studied electrolyte loss from profuse sweating in soccer-team players and evaluated the relationship between this source of iodine loss and iodine deficiency. Thirteen male soccer-team players and 100 sedentary students from the same high school were evaluated for 8 d, during which the players were training. The authors analyzed 208 sweat samples to determine losses of iodine, sodium, potassium, and calcium in sweat. Excretion of urinary electrolytes by the subjects was also measured. The mean losses of iodine, sodium, potassium, and calcium in sweat following a 1-hr game were 52 microg, 1,896 mg, 248 mg, and 20 mg, respectively; the ratios of sweat loss to urinary daily loss of the four electrolytes were 0.75, 0.2, 1.88, and 0.92, respectively. Urinary iodine was significantly (p < .02) lower than the normal level of 50 microg/gm creatinine in 38.5% of the soccer players, compared with 2% of the sedentary students. Forty-six percent of the players had Grade I goiter, compared with a mere 1% of the sedentary students (p < .01). The results of the study suggest that loss of iodine through profuse sweating may lead to iodine deficiency, and loss of electrolytes through sweating may have a dietary significance for heat-stressed individuals or for individuals who perform heavy workloads.     

Metabolic balances of cadmium, copper, manganese, and zinc in man.

Balance studies of cadmium, copper, manganese, and zine were carried out under constant dietary conditions in eight adult males during two calcium intake levels of 200 and 800 mg/day and in an additional single case during a calcium intake of 1500 mg/day. The dietary content and the excretions of these elements in urine and stool were determined. The mean dietary content of cadmium was 32.9 micrograms/day, of copper 1020 micrograms/day, of manganese 2130 micrograms/day, and of zinc 12.4 mg/day. The ratio of the fecal/urinary cadmium excretion was approximately 1.5 and the main pathway of excretion of the other three elements was via the intestine, while the urinary excretions were very low. The different trace element balances were either slightly negative or in equilibrium, except that the zinc balances was positive in 50% of the cases. All balances should be considered maximal values, as the losses in sweat were not determined. The calcium intake level had little effect on the excretion and retention of these trace elements.     

Iodide excretion before and after revision of goiter prophylaxis (Dutch Nutrition Surveillance System).

To assess the iodine supply in The Netherlands after the revision of the goiter prophylaxis measures (Bread Act of 1982, with an increase of iodine content of bread salt) the data of a nationwide survey among Dutch elderly people conducted in 1984/1985 were analysed. Iodide excretion in 24 h urine samples was used as the main iodine status indicator. The data were compared with data on iodine nutriture obtained among an elderly population in The Netherlands before the revision of goiter prophylaxis. High prevalences (greater than or equal to 37%) of low iodine excretion (less than 0.78 mumol/24 h; 100 micrograms/24 h) were found for Dutch elderly people. Mean urinary iodide excretion was 0.95 mumol/24 h (121 micrograms/24 h) for men and 0.79 mumol/24 h (100 micrograms/24 h) for women which is low, especially among women, in comparison with the United States recommended dietary allowance (118 mumol/day = 150 micrograms/day). Consistent positive associations of iodide excretion were found with urinary potassium and sodium excretion, bread consumption and total iodine intake. Bread, as the iodine carrier chosen for goiter prophylaxis in The Netherlands, was found to be the main dietary iodine source. No improvement in iodine nutrition was found among the elderly studied in 1984/1985 in comparison with an elderly population seen in 1981. Therefore, it is concluded that the present measures regarding goiter prophylaxis in The Netherlands might be of limited effectiveness.     

天津市售食品碘含量及部分大学学生碘营养状况的研究

目的了解当前市售食品碘含量,部分大学生膳食碘营养状况,碘盐对膳食摄入碘的补充作用,以及尿碘测定结果对膳食碘的反映程度。方法分层随机采集日常市售食物278份,采用砷铈接触法测定食品碘含量,膳食记录法调查学生的7日膳食情况,砷铈催化分光光度法测定尿碘。结果47种、278份食物样品的检测表明,动物性食品的含碘量（7．8ug／100g～30．8ug／100g）高于植物性食品的含碘量（1．8ug／100g～16．1ug／100g）。膳食调查显示该类学生中以素食为主的占70．19％,以食物碘含量的实测值和膳食调查结果计算出由食物中摄入碘的量为（111．67±53．18）ug/d,而从碘盐中补充碘量（230．27±45．55）ug／d,那么从膳食中共可以摄入碘（341．95±89．58）ug/d。经尿肌酐校正后每克肌酐尿中碘含量中位数为271．28ug／gCr。经尿肌酐校正后的尿含碘量与膳食摄碘量呈正相关关系（0=0．463,P〈0．01）。结论这部分学生多数来自低收入家庭且膳食以素食食物为主,每日从膳食中摄入的碘量低于碘的推荐供给量（RDA）150ug,但是从加碘食盐中可以获得碘230．27ug,从而弥补膳食摄碘量的不足。     

Changes in iodine excretion in 50-69-y-old denizens of an Arctic society in transition and iodine excretion as a biomarker of the frequency of consumption of traditional Inuit foods

BACKGROUND: Iodine intake in Greenland has been hypothesized to exceed 10 times the recommended amount. The transition from a traditional Arctic society may change the iodine intake, but no field studies have been performed. OBJECTIVE: We aimed to ascertain iodine intakes, factors affecting iodine intake in circumpolar populations, and the usefulness of urinary iodine excretion as a biomarker for validation of Inuit food-frequency questionnaires. DESIGN: Data were collected in a cohort study of 4 Greenland population groups: Inuit living in the capital city, the major town, and settlements in East Greenland and non-Inuit. Supplement use and lifestyle factors were evaluated with questionnaires, and dietary habits were ascertained with a food-frequency questionnaire. Iodine was measured in spot urine samples. RESULTS: One percent of the population of Greenland was invited, and the participation rate was 95%. Less than 5% of Inuit but 55% of non-Inuit had urinary iodine excretion < 50 microg/24 h. Median urinary iodine excretion declined with the degree of decrease in the traditional lifestyle: it was 198, 195, 147, and 58 microg/24 h among Inuit in settlements, town, and city and in non-Inuit, respectively (P < 0.001). Participants were divided into diet groups calculated from Inuit food frequency. Iodine excretion decreased with increasing intake of imported foods (P < 0.001). In regression models, type of diet and the subject's lifestyle, sex, weight, ethnicity, and intake of iodine-containing supplements affected urinary iodine excretion. CONCLUSIONS: Circumpolar non-Inuit are at risk of iodine deficiency. Departure from the traditional Inuit diet lowers iodine intake, which should be monitored in Arctic societies. Urinary iodine excretion may be a useful biomarker of traditional Inuit food frequency.     

Assessment of sodium and iodine intake among university students in Casablanca,Morocco

IntroductionIodine deficiency is still a matter of public health concern despite salt fortification and especially with global recommendations to lower salt intake, this is mainly due to dietary habits. University students have a diet based on street food high in sodium and low in other micronutrients (i.e. iodine and potassium). In this study, we aim to measure sodium and iodine levels in university students to assess their risk of developing complications later in life.MethodologyA sample of 120 students aged between 18 and 25 years old was recruited and asked to collect their 24-hours urine samples in special containers containing. Samples were stored then analyzed for sodium, potassium, iodine and creatinine levels.ResultsThe average urinary excretion of sodium was 3066.8 ± 1196.0 mg/day. Overall, 72.6% of participants consume more than 2 g/day of sodium. Average potassium intake is 1805.9 ± 559.4 mg/day, and all participants consume less than the adequate amount. Daily urinary excretion of iodine is 135.6 ± 88.9 mg/day, and 69.2% of participants consume less than the recommended amount. Sodium, potassium and iodine intakes were higher in male participants (P-values = 0.008; 0.044 and 0.003, respectively). The lowest average iodine intake was observed in underweight participants (119.4 ± 31.4) with 87.5% of underweight participants and 80% of female participants below the recommended intake.ConclusionSodium intake is high while iodine intake is low in this studied population, especially in women.     

Selenium intake and metabolic balance of 10 men from a low selenium area of China

Selenium intake and urinary and fecal Se excretion of 10 healthy men from a low Se area in China were determined for three consecutive days, in summer, fall, and winter of 1983, and the spring of 1984 while self-selected diets were being consumed. Mean daily Se intake was 8.8 micrograms/day with a range of 2.3-35.5 micrograms/day, and was far below the recommended range of safe and adequate Se intake of 50-200 micrograms Se/day (National Academy of Sciences/National Research Council). Mean urinary and fecal Se outputs were 3.7 and 3.4 micrograms Se/day, respectively. Mean Se balance during this time was +1.8 micrograms Se/day. Apparent absorption of Se approximated 57%. The low Se intake in this area is a cause for concern since the residents of Molimo may be at risk for Se deficiency diseases.     

Experience with iodine prophylaxis in the province of Bolzano

Since 1981 in the province of Bolzano a "free-choice" iodine prophylaxis with iodinated dietary salt has been implemented. An epidemiological survey carried out in 1982 in 3109 schoolchildren living in this region showed an incidence of endemic goiter grade 1B-3 (WHO classification) of 23.6 +/- 14.0% and an urinary iodine excretion of 10.2 +/- 8.0 micrograms/l (colorimetric analysis) compared to the values of 39.6 +/- 17.7 micrograms/l found in a similar population of schoolchildren living in a non goitrous urban area in Northern Italy (Padua). This program of iodine prophylaxis was advertised through the local mass media. A further epidemiological survey, performed in the whole province in the year 1990, involving 1046 schoolchildren, randomly selected, showed an average goiter incidence of 1.6 +/- 1.3% and a urinary iodine excretion of 137.1 +/- 104.4 micrograms/l (ICP-MS analysis) in comparison to the values of 182.6 +/- 131.7 micrograms/l seen in the schoolchildren of the town of Padua. During the period of iodine prophylaxis the content of iodine in the commercially available iodinated dietary salt was also estimated. In 1990 the average content was 31.0 mg/kg and in 1997 was 27.1 mg/kg. These data therefore confirm the usefulness of iodinated salt in the prophylaxis of endemic goiter.     

Comparison of isoflavones among dietary intake, plasma concentration and urinary excretion for accurate estimation of phytoestrogen intake

Biological effects of dietary isoflavones, such as daidzein and genistein are of interest in preventive medicine. We estimated the dietary intake of isoflavones from dietary records and compared the values with the plasma concentrations and urinary excretions in Japanese middle-aged women. The dietary intake of daidzein and genistein was 64.6 and 111.6 mumol /day/capita (16.4 and 30.1 mg/day/capita), respectively. The isoflavones intake was mostly attributable to tofu, natto and miso. The median of plasma daidzein and genistein concentration was 72.46 and 206.09 nmol/L, respectively. The median of urinary excretion was 20.54 mumol /day for daidzein, 10.79 for genistein, 15.74 for equol and 1.64 for O-desmethylangolensin (O-DMA). Equol and O-DMA were excreted by 50% and 84% of all participants, respectively. Equol metabolizers were significantly lower the plasma and urinary daidzein and urinary O-DMA. The dietary intake of daidzein and genistein after the adjustment for total energy intake was significantly correlated with the urinary excretion (r = 0.365 for daidzein and r = 0.346 for genistein) and plasma concentration (r = 0.335 for daidzein and r = 0.429 for genistein). The plasma concentration of isoflavones was also significantly correlated with the urinary excretion. We conclude that in epidemiological studies measurements of plasma concentration or urinary excretion of these isoflavones are useful biomarkers of dietary intake and important for studies on their relation to human health.     

Iodine status in vegans consuming a living food diet

The dietary intake and urinary output of iodine and the thyroid activity was measured in 12 living food eaters (people consuming uncooked, Lactobacilli rich vegan food) and omnivores. Seven day food record was used for calculating the dietary iodine intake, instrumental neutron activation analysis for measuring the urinary iodine output and RIA for determining of the thyroid hormones (TSH and FT4). The living food eaters were divided into two groups according to urinary iodine output: high iodine group (≥900 ug/d) and low iodine group (<200 ug/d). Thyroid activity in both groups was with in normal range. Dietary intake of iodine was dependent on the the use of seaweed. The highest amounts of dietary iodine observed in the present study, as assessed by the the urinary iodine output, can be harmful for susceptible subjects. On the other hand the calculated intake of iodine by living food eaters didn't fill the RDA. As an conclusion on a living food diet one has to ensure the sufficient intake of iodine by consuming seaweed or Kelp tablets daily. However the intake of these preparations needs to be kept at reasonble limits due to their possible high iodine content. More information of the iodine content of different seaweeds and seaweed products is needed.     

Electrolyte Loss in Sweat and Iodine Deficiency in a Hot Environment

The authors studied electrolyte loss from profuse sweating in soccer-team players and evaluated the relationship between this source of iodine loss and iodine deficiency. Thirteen male soccer-team players and 100 sedentary students from the same high school were evaluated for 8 d, during which the players were training. The authors analyzed 208 sweat samples to determine losses of iodine, sodium, potassium, and calcium in sweat. Excretion of urinary electrolytes by the subjects was also measured. The mean losses of iodine, sodium, potassium, and calcium in sweat following a 1-hr game were 52 μg, 1,896 mg, 248 mg, and 20 mg, respectively; the ratios of sweat loss to urinary daily loss of the four electrolytes were 0.75, 0.2, 1.88, and 0.92, respectively. Urinary iodine was significantly (p < .02) lower than the normal level of 50 μg/gm creatinine in 38.5% of the soccer players, compared with 2% of the sedentary students. Forty-six percent of the players had Grade I goiter, compared with a mere 1 % of the sedentary students (p < .01). The results of the study suggest that loss of iodine through profuse sweating may lead to iodine deficiency, and loss of electrolytes through sweating may have a dietary significance for heat-stressed individuals or for individuals who perform heavy workloads.     

Effect of season and exercise on dermal nitrogen losses and their relation to urinary nitrogen excretion

The present study was designed to estimate dermal nitrogen losses in summer and winter under the conditions of minimal daily activities, on a diet of standard Japanese protein intake level and to determine whether the increased dermal nitrogen losses induced by hot climate or exercise were compensated for by the decrease in urinary nitrogen excretion. Six healthy male university students served as the subjects. The daily dermal nitrogen losses (mean +/- SD) were 0.22 +/- 0.07 g or 3.10 +/- 0.58 mg/kg in winter and 0.44 +/- 0.19 g or 6.35 +/- 2.46 mg/kg in summer, showing significantly higher dermal nitrogen losses in summer than in winter. On the contrary, urinary nitrogen excretion tended to be larger in winter than in summer. Thus, renal compensation seemed to exist for the seasonal changes in dermal nitrogen losses. In the summer experiment, the subjects took light exercise besides the minimal daily activities for a 2-day exercise period. The pooled mean of daily dermal nitrogen losses during the exercise period was significantly larger than that during the sedentary period, while the urinary nitrogen excretion was almost the same in the two periods. No compensatory reduction in the urinary nitrogen excretion during the exercise period was observed under the conditions of the present study.     

Goiter prevalence and urinary excretion of iodine in a sample of school age children in the city of Rome

The aim of the study was the assessment of the urinary iodine excretion and the evaluation of thyroid volume compared with clinical examination in 1040 schoolchildren (6-14 years old), living in Rome. Mean urinary iodine excretion was 98.52 +/- 49.81 micrograms/l (median 92 micrograms/l). Thyroid enlargement, as assessed by palpation, was found to be grade 1A in 35.4% of the children, grade 1B in 9.6% and grade 2 in 0.2%. Thyroid volume, determined by ultrasound, increased with age, was significantly correlated with body surface area and was significantly higher in females, as compared to males, in the 11 and 12 years old group. Eleven children (1.9%) were negative at palpation (grade 0) but showed thyroid enlargement by ultrasound. The prevalence of goiter determined by ultrasound resulted to be 4.7%.     

Dietary evaluation of a low-iodine diet in Korean thyroid cancer patients preparing for radioactive iodine therapy in an iodine-rich region

BACKGROUND/OBJECTIVES

Despite the importance of a low-iodine diet (LID) for thyroid cancer patients preparing for radioactive iodine (RAI) therapy, few studies have evaluated dietary intake during LID. This study evaluated the amount of dietary iodine intake and its major food sources during a typical diet and during LID periods for thyroid cancer patients preparing for RAI therapy, and examined how the type of nutrition education of LID affects iodine intake.

SUBJECTS/METHODS

A total of 92 differentiated thyroid cancer patients with total thyroidectomy were enrolled from Seoul National University Hospital. All subjects completed three days of dietary records during usual and low-iodine diets before ¹³¹I administration.

RESULTS

The median iodine intake was 290 µg/day on the usual diet and 63.2 µg/day on the LID. The major food groups during the usual diet were seaweed, salted vegetables, fish, milk, and dairy products and the consumption of these foods decreased significantly during LID. The mean energy intake on the LID was 1,325 kcal, which was 446 kcal lower than on the usual diet (1,771 kcal). By avoiding iodine, the intake of most other nutrients, including sodium, was significantly reduced during LID (P < 0.005). Regarding nutritional education, intensive education was more effective than a simple education at reducing iodine intake.

CONCLUSION

Iodine intake for thyroid cancer patients was significantly reduced during LID and was within the recommended amount. However, the intake of most other nutrients and calories was also reduced. Future studies are needed to develop a practical dietary protocol for a LID in Korean patients.     

Urinary orotic acid excretion in sheep: effects of nitrogen, glucose and arginine

The urinary excretion of orotic acid was investigated in four sheep. Nitrogen and energy intake were varied by infusions of urea and glucose. The effect of arginine infusion was also investigated. Nitrogen intake of 10.4 g/d led to a urinary excretion of orotic acid of 357 +/- 61 micrograms/d. Increasing N intake to 21.4 g/d significantly increased urinary orotic acid excretion to 747 +/- 46 micrograms/d. Glucose infusion (300 g/d) significantly decreased orotic acid excretion when N intake was 10.4 g/d, whereas arginine infusion (2.3 g/d) did not alter the excretion of orotic acid under these conditions. When arginine was infused at higher N intake (21.4 g/d), orotic acid excretion decreased from 822 +/- 74 to 624 +/- 46 micrograms/d. It is concluded that increasing N intake is accompanied by an enhanced urinary excretion of orotic acid. This excretion of orotic acid is significantly modified by glucose or arginine.     

Effect of zinc intake on copper excretion and retention in men

To determine the influence of zinc intake on copper excretion and retention, nine men consumed diets containing 2.6 mg of copper/day and 1.8, 4.0, 6.0, 8.0, 18.5 or 20.7 mg of zinc/day for one- or two-week periods in a 63-day study. Copper and zinc in the diet and copper in plasma were determined weekly; fecal copper was determined daily and averaged within each week. The weekly mean (+/-SEM) plasma copper concentrations (81 +/- 3.3 to 100 +/- 5.8 micrograms/dl) remained within the normal range throughout the study. Fecal copper and apparent copper retention were influenced by the level of dietary zinc and the duration it was fed. When 18.5 mg of zinc/day was fed for two consecutive weeks following a lower zinc intake, fecal copper was elevated and apparent copper retention was reduced after a one-week lag. Thus, an intake of zinc only 3.5 mg/day above the RDA for men reduced apparent retention of copper at an intake of 2.6 mg/day.     

Daily urinary excretion of bisphenol A

Objectives  Concerns over dietary exposure to bisphenol A (BPA), an endocrine disruptor, have been raised because BPA is contained in resins and plastics commonly used for the preservation of food and beverages. The purpose of the present study was to assess daily intake levels of BPA in a group of male subjects by measuring total urinary BPA (free BPA plus BPA released by treatment with β-glucuronidase), as well as determining intra-individual variation in BPA excretion. Methods  Twenty-four-hour urine was collected from 5 subjects for 5 consecutive days for the evaluation of between-day variation in urinary BPA excretion and from 36 male subjects for the estimation of the level of daily BPA intake. BPA in the urine samples was measured by GC/MS/MS following enzymatic hydrolysis of BPA glucuronate, solid phase extraction, and derivatization. Results  A large between-day variation was found over 5 days for the daily excretion of urinary BPA in the 5 subjects. The daily excretion of urinary BPA was distributed log-normally in the 36 male subjects, with the median value being 1.2 μg/day (range: <0.21–14 μg/day), which was far below the Tolerable Daily Intake (0.01 mg/kg bw) recommended by a scientific committee in the European Commission in 2002. However, the maximum estimated intake per body weight (0.2 μg/kg/day) was only one order of magnitude lower than the reported lowest level for reproductive/behavioral effects in pregnant mice (2 μg/kg/day). Conclusions  Measuring urinary BPA in urine is a suitable approach for estimating short-term BPA intake levels in individuals and/or estimating the average exposure level of populations. Urine analyses will be increasingly important in the human health risk assessment of BPA.     

A 4-day sodium-controlled diet reduces variability of overnight sodium excretion in free-living normotensive adolescents

The present analysis examined changes in the variability of overnight sodium excretion in 84 free-living adolescents (ages 15 to 19 years) on a 4-day sodium-controlled diet in which foods provided were selected by adolescents from an extensive list of menu items. The only selection criterion imposed was that foods selected for each day contain 4,000+/-200 mg sodium. Adolescents collected overnight urine samples. Repeated measures analysis of variance tested the effect of diet day on overnight sodium excretion, overnight urinary sodium concentration, and overnight urinary volume. Variance ratio test evaluated changes in overnight sodium excretion variance across days. Day 4 overnight sodium excretion was statistically lower than days 1 to 3 (1.84 vs 6.54, 5.94, and 5.52 mEq/h [1.84 vs 6.54, 5.94, and 5.52 mmol/h]). Day 4 overnight urinary sodium concentration was lower than days 1 to 3 (32.16 vs 119.64, 109.61, and 111.32 mEq/L [32.16 vs 119.64, 109.61, and 111.32 mmol/L]). The variance of overnight sodium excretion from day 1 to day 4 was reduced 10-fold from 20.1 mEq/h (20.1 mmol/h) to 1.90 mEq/h (1.90 mmol/h). Daily overnight urine volumes remained constant, averaging 451.7 mL/day. The dietary protocol successfully reduced the variability of sodium intake as estimated by overnight sodium excretion in free-living adolescents. The protocol could be expanded to include baseline values, additional days of sodium control, and varying levels of dietary sodium intake.