Basal urinary zinc/creatinine ratio as an indicator of dietary zinc intake in healthy adult women

Dietary Zinc and Incident Calcium Kidney Stones in Adolescence

PURPOSE

We determined the association between dietary zinc intake and incident calcium kidney stones in adolescents. We also examined the relationship between dietary zinc intake and urinary zinc excretion between cases and controls.

MATERIALS AND METHODS

We conducted a nested case-control study within a large pediatric health care system. Three 24-hour dietary recalls and spot urine chemistry analyses were obtained for 30 participants 12 to 18 years old with a first idiopathic calcium based kidney stone and 30 healthy controls matched for age, sex, race and month of enrollment. Conditional logistic regression models were used to estimate the association between daily zinc intake and incident calcium kidney stones, adjusting for dietary phytate, protein, calcium, sodium and oxalate. Multivariable linear regression was used to estimate the association between dietary and urine zinc, adjusting for urine creatinine and dietary phytate and calcium.

RESULTS

Cases had lower daily zinc intake (8.1 mg) than controls (10 mg, p = 0.029). Daily zinc intake of boys and girls with calcium stones was 2 mg and 1.2 mg less, respectively, than the daily intake recommended by the Institute of Medicine. Odds of incident stones were reduced by 13% for every 1 mg increase in daily zinc intake (OR 0.87, 95% CI 0.75-0.99). There was an estimated 4.5 μg/dl increase in urine zinc for every 1 mg increase in dietary zinc (p = 0.009), with weak evidence of a smaller increase in urine zinc in cases than in controls (interaction p = 0.08).

CONCLUSIONS

Decreased dietary zinc intake was independently associated with incident calcium nephrolithiasis in this population of adolescents.

Tissue zinc levels in a child with hypercalprotectinaemia and hyperzincaemia: A case report and a review of the literature

BACKGROUND

A girl suffering from a rare syndrome of unknown aetiology, termed hypercalprotectinaemia, was evaluated for tissue zinc status, because calprotectin is a protein which chelates Zn at multiple binding-sites, which might have affected the distribution of Zn in her body.

METHODS

Measurement of serum, urine, hair and nail zinc (Zn) concentration, complemented with measurement of total Zn in ultrafiltrates of plasma.

RESULTS

Her serum Zn concentration was 105-133 μmol/L. Zn levels in her hair (102 μg/g), nail (90 μg/g) and urine (3-12 μmol/L; 20-80 μg/dL) were all at the lower end of the reference intervals described in the sparse literature. Zn concentrations in ultrafiltrates of plasma were below the detection limit (<100 nmol/L). Thus, the elevated serum Zn did not translate into a similarly increased level of Zn in any of the tissues tested, nor in free Zn concentrations. Instead it appeared to be a result of Zn being chelated to binder proteins, most probably calprotectin.

CONCLUSION

Her grossly elevated serum calprotectin concentration is probably able to raise circulating total Zn concentrations without raising ionized concentrations, but this Zn remains confined to the circulating blood as well as to excreted body fluids, particularly faeces.

Maternal exposure to low-level heavy metals during pregnancy and birth size

We evaluated the effect of environmental, low-level exposure to heavy metals during pregnancy, as estimated by urine analysis, on birth size of the newborns. Spot urine samples were collected from unexposed 78 pregnant women in Tokyo during 2007 and 2008. The urinary concentrations of beryllium (Be), copper (Cu), arsenic (As), zinc (Zn), selenium (Se), molybdenum (Mo), cadmium (Cd), tin (Sn), antimony (Sb), and lead (Pb) were measured by ICP-MS. The birthweight (BW), length (BL) and head circumference (HC) of the newborns delivered to the subjects were measured and relationship with urinary metal concentration was examined. The geometric mean concentration of urinary Be, Cu, As, Zn, Se, Mo, Cd, Sn, Sb, and Pb were 0.031, 12.8, 393, 76.9, 37.6, 79.0, 0.766, 0.232, < 0.21, 0.483 microg g-creatinine(-1), respectively. The mean birth size of the newborn was close to the national average value in Japan. Stepwise multiple regression analysis using birth size as a dependent variable and urinary metal concentrations and covariates as independent variables extracted urinary Cd with a significant negative standardized partial regression coefficient (beta) for BW along with gestational age and maternal BMI. For HC, Sn was selected with a negative beta. The present study suggested that even a low-level Cd body burden of general population has slight but significant negative effect on BW.

Renal zinc clearance/glomerular filtration rate ratio as an indicator of marginal zinc deficiency associated with iron deficiency in childhood

OBJECTIVE

To evaluate the usefulness of renal zinc clearance/glomerular filtration rate ratio (R(ClZn)/GFR) as an indicator of marginal zinc deficiency that is generally associated with iron deficiency in childhood.

METHODS

Zinc status was evaluated in 36 iron-deficient children (22 boys and 14 girls) who ranged in age from 1 to 10 years using serum zinc concentration and U(Zn/Cr) and R(ClZn)/GFR ratios. The results were compared with the zinc status of 36 similar-aged healthy children (24 boys and 12 girls).

RESULTS

Serum zinc concentrations were 96.72 +/- 2.13 microg/dL and 93.93 +/- 1.95 microg/dL in iron-deficient and healthy subjects, respectively (p > 0.05). U(Zn/Cr) ratios were 0.54 +/- 0.04 microg/mg and 0.88 +/- 0.04 microg/mg (p < 0.0001); R(ClZn)/GFR ratios were 2.27 x 10(-3) +/- 0.20 and 3.32 x 10(-3) +/- 0.20 (p < 0.001) in iron-deficient and healthy subjects, respectively. Individual values of R(ClZn)/GFR and U(Zn/Cr) ratios correlated with hemoglobin (Hb) concentrations (r = 0.34, p < 0.01 and r = 0.26, p < 0.05). Data grouped according to the ranges of Hb concentrations and R(ClZn)/GFR and U(Zn/Cr) ratios fit the following equations: The statistically significant difference in U(Zn/Cr) and R(ClZn)/GFR ratios between groups indicates decreased urinary estimation of marginal zinc deficiency, whereas no change was observed in serum zinc concentrations. According to the regression equation, it can be postulated that the R(ClZn)/GFR ratio is a linear function of Hb concentration and the U(Zn/Cr) ratio.

CONCLUSION

R(ClZn)/GFR ratio was a reliable indicator for reduction in urinary zinc excretion; it estimated the marginal zinc deficiency associated with iron deficiency. The R(ClZn)/GFR ratio can be calculated using one sample of blood and urine; thus it could serve as an alternative indicator of marginal zinc deficiency, especially in routine health care.

Zinc status and bone mineralisation in adolescent girls

The aim of the project was to assess the relationship between zinc status and bone mineralisation in pre-menarcheal adolescent girls. One hundred and thirty-nine healthy pre-menarcheal girls (Tanner pubic hair stage < or = 4), aged 12.4 +/- 1.0 years, had two visits at an interval of 2 years. Serum and urine zinc concentrations (Zn S; Zn U; Zn U/ creatinine), insulin-like growth factor 1 (IGF-I), and markers of bone turn-over, i.e. osteocalcin and parathormone (PTH), concentrations were measured at the first visit. Lumbar (L2-L4) bone mineral content and density (BMC, BMD) were measured at both visits. BMC and BMD and their increase at the follow-up after 2 years were compared with biochemical data by multiple regression. The stage of puberty was added as a covariable in the analysis. At the first visit, a significant correlation was found between sexual maturity and initial BMC, BMD, height, weight, and IGF-I. Zn S was negatively correlated with osteocalcin. Zn U showed a positive correlation with BMC, BMD, IGF-I, height, weight, and PTH. At the second visit, sexual maturity showed a positive correlation with BMD and weight increments and a negative one with BMC and height gains. Zn S was significantly related with BMD increase. These correlations suggest that zinc plays a role in normal growth and bone mineralisation during puberty onset.