This study measured rubidium by instrumental neutron activation analysis in transitional breast milk from 40 healthy mothers in Mashhad, Iran, 3 to 15 days after delivery. The mean was 32.176 ppm on a dry weight basis, which the authors describe as among the highest values reported. Rubidium did not correlate with maternal or infant characteristics.
Key numbers
- Rubidium in transitional breast milk: mean 32.176 ppm dry weight (SD 21.193), median 28.195, minimum 8.660, maximum 107.210 ppm, n 40 (Findings, p. 694; Abstract).
- Unit conversion (trivial): 32.176 ppm equals 32.176 mg/kg, that is 32,176 µg/kg dry weight.
- Individual values in Table 1 range from 8.659 to 107.210 ppm (Table 1, p. 694); the text rounds the minimum to 8.660.
- No significant correlation of rubidium with maternal weight or age (P 0.06 and 0.05) or newborn weight, age or sex (P 0.07, 0.2, 0.2) (Abstract; Findings, p. 694).
- The discussion quotes earlier reports of rubidium in serum (78 to 317 µg/L), whole blood (900 to 4145 µg/L) and a mean intake of 2.2 ± 0.3 mg/day; these are cited values, not measured in this study (Discussion, p. 695).
Methods (brief)
Milk (10 to 15 mL, hand expressed) was collected January to September 2011 at Razavi hospital, dried at 80 °C for 48 h, powdered, and 300 mg portions were irradiated in a research reactor (thermal neutron flux 5 x 10^11 n/cm2/s for 5 h). Rubidium was counted after 30 to 38 days of decay with a high-purity germanium detector. A reference apple leaves material from the Esfahan Nuclear Technology Center was used for quality control.
Evidence fitness
Supports occurrence of rubidium in transitional human milk from one Iranian city, on a dry weight basis. It does not support infant intake estimates (milk volume and water content are not given), toxicity claims, or reference ranges. The authors call rubidium a potential toxic element on the basis of earlier literature only.
Limitations
Single city, 40 mothers, one lactation stage. Results are dry weight only, so they cannot be compared directly with wet weight values. The quality control material is not an internationally certified reference and recovery is not reported. The authors themselves note that their values are high relative to the literature and may reflect method differences. Funded by the Atomic Energy Organization of Iran, which also hosted the analysis.
Related evidence
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