VARIATIONS IN PLASMA VOLUME AND MICRONUTRIENT BIOMARKERS ACROSS THE MENSTRUAL CYCLE AMONG WOMEN OF REPRODUCTIVE AGE
Open Access
- Author:
- Aguree, Sixtus
- Graduate Program:
- Nutritional Sciences
- Degree:
- Doctor of Philosophy
- Document Type:
- Dissertation
- Date of Defense:
- June 04, 2019
- Committee Members:
- Alison D. Gernand, Dissertation Advisor/Co-Advisor
Alison D. Gernand, Committee Chair/Co-Chair
Laura E. Murray-Kolb, Committee Member
Lacy M. Alexander, Committee Member
Francisco J. Diaz, Outside Member
Matthew L. Reimherr, Special Member - Keywords:
- estrogen and blood volume
progesterone and blood volume
blood volume
ovarian cycle
ovarian hormones
nutritional biomarkers
indocyanine green
reproductive hormones and nutrition
intravascular volume
hemodilution and biomarkers - Abstract:
- Background: Micronutrient deficiencies are a global health problem most commonly occurring in women of reproductive age and children. Plasma volume is an important marker of health status and large changes have been associated with variation in plasma-based micronutrient biomarkers. Further, some evidence suggests that plasma volume and micronutrient concentrations may vary across the menstrual cycle. Accurate knowledge of micronutrient variability in the prepregnancy state would help improve decisions on appropriate times in the menstrual cycle to assess a woman’s nutritional status and to evaluate micronutrient deficiencies in a population. Accurate determination of micronutrient concentrations and plasma volume in the nonpregnant state could also improve how changes during pregnancy are estimated, and ultimately could be useful in deciding when to intervene in pregnancy. Objectives: The objective of this study was to prospectively evaluate the variations in plasma volume and selected micronutrient biomarker concentrations across the menstrual cycle, under free-living conditions, in a cohort of healthy women of reproductive age. The primary outcomes were 1) plasma volume in the early and late follicular and midluteal phases; and changes in plasma volume between timepoints; 2) serum zinc, copper, magnesium, manganese, iron, ferritin, and retinol concentrations and total circulating mass at the three timepoints and prevalence of deficiencies, as well as changes in concentrations between timepoints; and 3) the relationship between plasma volume and micronutrient biomarkers. Research Design and Methods: This was a longitudinal prospective study wherein subjects were examined at three time points within a single menstrual cycle: the early follicular phase (EFP; ~day 2), the late follicular phase (LFP; ~day 12), and the midluteal phase (MLP; ~day 21) — based on a 28-day cycle length. The actual days of study visits were adjusted for the length of the woman's menstrual cycle and urinary hormone results from a fertility monitor. Visits were timed to key ovarian states and the hormone concentrations helped us determine those states. Blood samples were collected followed by the injection of a bolus dose of 0.25 mg/kg body weight of indocyanine green dye (ICG). Starting at 2 minutes post-ICG injection, a series of 5 blood samples timed to occur every 45 seconds were collected and used to estimate plasma volume. Pre-injection blood samples were used to measure ovarian hormones (serum estradiol and progesterone) and micronutrient biomarkers (serum zinc, copper, magnesium, manganese, iron, ferritin, retinol), and to conduct a complete blood count. All biomarkers were measured at three timepoints in the cycle. For practical purposes, we assumed that serum and plasma concentrations of micronutrients are comparable, and therefore, total mass for each biomarker was calculated by multiplying plasma volume and serum concentrations. Linear mixed-effects models were used to investigate the bivariate association between menstrual phase and plasma volume, and menstrual phase and micronutrient biomarkers. Fractional polynomial regression (prediction plots) were used to examine bivariate relationships between plasma volume and biomarkers including micronutrient biomarker concentrations and mass. Results: A total of 47 women were enrolled in the study and 35 completed all study visits. Blood data was available for 45 subjects at visit 1 (EFP), 39 at visit 2 (LFP), and 35 at visit 3 (MLP). The mean ± SD plasma volume was highest at 2276 ± 478 mL in the EFP; it declined slightly to 2232 ± 509 mL in the LFP and 2228 ± 502 mL in the MLP. On average, plasma volume fell by 55 mL (2.4%) between EFP and MLP (P = 0.536). The mean ± SD concentrations for micronutrients in EFP were 81.8 ± 16.2 µg/dL (zinc), 80.1 ± 12.8 µg/dL (copper), 17.9 ± 1.4 mg/L (magnesium), 1.51± 1.97 µg/L (manganese), 106.7 ± 1.7 µg/dL (iron), 26.4 ± 2.3 µg/L (ferritin), and 39.4 ± 9.3 µg/dL (retinol). All micronutrient biomarker concentrations decreased between EFP and LFP. Reductions in zinc and magnesium concentrations were relatively large, 6.6% (P = 0.009) and 4.6%( P < 0.001), respectively; changes for other micronutrients ranged from <1 to 4.3%, and were not statistically significant (all P > 0.05). Correspondingly, the prevalence of micronutrient deficiencies changed across the cycle. Overall, the highest prevalence of deficiencies was in the LFP and MLP. For instance, zinc deficiencies rose from 22% to 37% from EFP to MLP and magnesium went up from 17% to 49%. Plasma volume and biomarker concentrations showed a weak correlation or no correlation. Values were -0.05 to 0.10 (all P > 0.05) across all biomarkers. The correlations between plasma volume and biomarker mass showed a strong positive correlation: 0.26 to 0.95 (all P < 0.01). The correlation coefficient was greater than 0.70 (P < 0.001) for the mass of five out of the eight biomarkers. Conclusions: The results from this study suggest that the menstrual cycle state or phase has a relatively small influence on plasma volume in healthy nonpregnant women of reproductive age. Changes in serum zinc and magnesium concentrations across the menstrual cycle were quite large. In healthy nonpregnant women, plasma volume and micronutrient concentrations were not associated. Therefore, in normal healthy women of reproductive age, it is not expected that plasma volume is needed to aid in the interpretation of micronutrient status. Though more research is needed to determine whether menstrual phase should be considered in the design of studies examining micronutrient biochemical markers in healthy nonpregnant women, the results from this study suggest that the menstrual cycle phase may influence how concentrations of zinc and magnesium are interpreted. Further work is needed to build a body of evidence on the variability of micronutrient biomarker concentrations across the menstrual cycle, and to determine whether the menstrual phase should be considered in evaluating micronutrient status in women of reproductive age, in research and clinical practice. Such studies will also provide the basis on which to determine the appropriate time to measure micronutrient status that reflects the true status of an individual and at the population level.