The development of reference values of trace elements is recognized as a fundamental prerequisite for the assessment of trace element nutritional status and health risks. In this study, a total of 1400 pregnant women aged 27.0 ± 4.5 years were randomly selected from the China Nutrition and Health Survey 2010–2012 (CNHS 2010–2012). The concentrations of 14 serum trace elements were determined by high-resolution inductively coupled plasma mass spectrometry. Reference values were calculated covering the central 95% reference intervals (P2.5–P97.5) after excluding outliers by Dixon’s test. The overall reference values of serum trace elements were 131.5 (55.8-265.0 μg/dL for iron (Fe), 195.5 (107.0–362.4) μg/dL for copper (Cu), 74.0 (51.8–111.3) μg/dL for zinc (Zn), 22.3 (14.0–62.0) μg/dL for rubidium (Rb), 72.2 (39.9–111.6) μg/L for selenium (Se), 45.9 (23.8-104.3) μg/L for strontium (Sr), 1.8 (1.2–3.6) μg/L for molybdenum (Mo), 2.4 (1.2–8.4) μg/L for manganese (Mn), 1.9 (0.6–9.0) ng/L for lead (Pb), 1.1 (0.3-5.6) ng/L for arsenic (As), 835.6 (219.8–4287.7) ng/L for chromium (Cr), 337.9 (57.0–1130.0) ng/L for cobalt (Co), 193.2 (23.6–2323.1) ng/L for vanadium (V), and 133.7 (72.1–595.1) ng/L for cadmium (Cd). Furthermore, some significant differences in serum trace element reference values were observed between different groupings of age intervals, residences, anthropometric status, and duration of pregnancy. We found that serum Fe, Zn, and Se concentrations significantly decreased, whereas serum Cu, Sr, and Co concentrations elevated progressively compared with reference values of 14 serum trace elements in pregnant Chinese women. The reference values of serum trace elements established could play a key role in the following nutritional status and health risk assessment.

Iron nutrition is important for the health of women of reproductive age, and defining the physiologic requirement for iron can help them accurately plan the iron intake. However, research on the physiologic requirement for iron in women is insufficient worldwide. This study aimed to further improve the methodology and get more precise data for the physiological requirements for iron in women of reproductive age on the basis of our previous study. Sixty-one women of reproductive age who had not been pregnant before and during the whole study were included from Hebei province, China in 2015. Each subject participated in a 2-week metabolic trial with consuming 50 mg of the stable isotope 58Fe, and were then followed for ~ 800 days. The abundance of 58Fe and the total iron concentration in the circulation were measured using multi-collector inductively-coupled plasma mass spectrometry and atomic absorption spectroscopy. The physiologic requirement for iron in women of reproductive age was then calculated. The average iron circulation rate was 80.4%, and the steady period started from about 1 year. The average physiological requirement for iron of 21 subjects obtained by formula calculation was 1.55 mg/d and 23.63 μg.kg− 1.d− 1 after adjustment for body mass, and that of 33 subjects obtained by linear regression was 1.29 mg/d, 20.98 μg.kg− 1.d− 1 after adjustment for body mass. The results by two methods showed no significant difference. The EAR and RNI calculated from this results was 11–13 mg/d and 15–18 mg/d, respectively, both of which were slightly lower than the recommended value in Chinese Dietary Reference Intake (2013). The physiological requirements for iron in women of reproductive age were in accordance with other studies, while the EAR and RNI calculated from which were slightly lower than Chinese present recommended value. ChiCTR, ChiCTR-OCH-14004302 . Registered 14 February 2014, http://www.chictr.org.cn/enindex.aspx

Background: Knowledge of the physiologic requirement for iron, the core index for the formulation of a dietary reference intake (DRI), is of great importance for the health of a pregnant woman and her fetus, and can help a mother accurately plan her iron supplementation. However, direct measurements of the physiologic requirement for iron during pregnancy are still lacking. Method: Eleven women of reproductive age from Hebei Province, China, who planned to become pregnant in the near future, were enrolled between January and March 2015 and included in the final analysis. Subjects participated in a 2-week metabolic trial in which they consumed 50 mg of the stable isotope ⁵⁸Fe, and were then followed for ~ 2 years. The abundance of ⁵⁸Fe and the total iron concentration in the circulation were measured using Multi-collector Inductively-Coupled Plasma Mass Spectrometry and Atomic Absorption Spectroscopy, respectively. The physiologic requirement for iron during pregnancy was then calculated by the formula derived from our previously published work. Results: The mean physiologic requirement for iron in the 11 subjects, across their entire pregnancies, was 3.05 mg.d^− 1 in total and 44.0 μg.kg^− 1.d^− 1 after adjustment for body mass. The physiologic requirements for iron in the first, second, and third trimesters were 2.04 mg.d^− 1, 3.26 mg.d^− 1, and 4.13 mg.d^− 1, respectively. When adjusted for body mass, the physiologic requirements for iron in different trimesters were 32.3 μg.kg^− 1.d^− 1, 46.9 μg.kg^− 1.d^− 1, and 55.7 μg.kg^− 1.d^− 1, respectively. Conclusion: We preliminarily explored the physiologic requirement for iron in pregnant women. The data demonstrated that pregnant women needed about twice iron than non-pregnant women. This research may be helpful for the design of future studies and the modification of iron DRIs. Trial registration: ChiCTR, ChiCTR-OCH-14004302. Registered 14 February 2014, http://www.chictr.org.cn/showproj.aspx?proj=5267