Cycle Effects Are Not Universal: A Case Study of Urinary C-Reactive Protein Concentrations in Rural Polish and Polish American Samples

Abstract

Objectives: We need to better understand how the menstrual cycle interacts with other biological systems, such the inflammation and immune response. One way to study this interaction is through C-reactive protein (CRP). Studies of CRP concentrations across the menstrual cycle have been inconsistent. This study explores menstrual cycle CRP variation in two geographically different samples of Polish and Polish American individuals.

Methods: Analyses were conducted on 76 Polish and 22 Polish American daily urine samples collected on the first day of menstruation until the start of their next period. CRP, estrone-3-glucuronide, and pregnanediol-3-glucuronide were assayed. Sample-specific linear mixed models were used to examine cycle effects and median CRP concentrations across cycle phases and between the start of menses and remainder of the cycle were compared using Kruskal-Wallace and Dunn tests.

Results: Polish and Polish American samples had distinct menstrual cycle CRP phenotypes. The Polish sample did not show cycle effects. The Polish American LMM demonstrated that CRP decreases after the first 3 days of menses (estimate -0.17, t-value -5.2). The KW and Dunn tests supported this. CRP concentrations were higher during the early follicular (median 0.406, p < 0.05), specifically the first 3 days of menstruation (median 0.466, p < 0.01), and lower in the luteal (median 0.277, p < 0.05).

Conclusions: Results suggest that changes in CRP during menstrual cycle are not universal across populations. In the Polish American sample, CRP was highest during the early follicular, specifically the first 3 days of menstruation, suggesting a potential relationship between the menstrual cycle and inflammation.

Keywords: C‐reactive protein; human biological variation; menses; menstrual cycle.

FIGURE 1

Figures showing Polish sample comparison of unscaled day and unscaled CRP concentrations (a), scaled day and unscaled CRP concentrations (b), and scaled day and scaled CRP concentrations (c). Individuals are Polish and aligned by ovulation (day 0). Red dots represent the first day of bleeding at the start and end of each cycle.

FIGURE 2

Figures showing Polish American sample comparison of unscaled day and unscaled CRP concentrations (a), scaled day and unscaled CRP concentrations (b), and scaled day and scaled CRP concentrations (c). Individuals are Polish American and aligned by ovulation (day 0). Red dots represent the first day of bleeding at the start and end of each cycle.

FIGURE 3

Box plots of Polish scaled CRP by cycle phase. No significant differences were found.

FIGURE 4

Boxplot of Polish scaled CRP between the first 3 days of menses and the remainder of the cycle. No significant differences were found.

FIGURE 5

Box plots of Polish American scaled CRP by cycle phase. A Kruskal‐Wallace test showed significant differences between groups (p < 0.05) and the post hoc Dunn Test showed that the early follicular was significantly higher than the periovulatory and the luteal phase (p < 0.05). * denotes significant (p < 0.05) group differences.

FIGURE 6

Box plots of Polish American scaled CRP comparing the first 3 days of menses (median = 0.466) with the rest of the cycle (median = 0.340). A Kruskal‐Wallace test showed significant group differences (p < 0.001).