Mental Disorders Among Mothers of Children Born Preterm: A Population-Based Cohort Study in Canada

BACKGROUND

Our aim was to examine the association between preterm delivery and incident maternal mental disorders using a population-based cohort of mothers in Canada.

METHODS

Retrospective matched cohort study using Manitoba Centre for Health Policy (MCHP) administrative data in Manitoba. Mothers who delivered preterm babies (<37 weeks gestational age) between 1998 and 2013 were matched 1:5 to mothers of term babies using socio-demographic variables. Primary outcome was any incident mental disorder within 5 years of delivery defined as any of (a) mood and anxiety disorders, (b) psychotic disorders, (c) substance use disorders, and (d) suicide or suicide attempts. Multivariable Poisson regression model was used to estimate the 5-year adjusted incidence rate ratios (IRRs).

RESULTS

Mothers of preterm children (N   =   5,361) had similar incidence rates of any mental disorder (17.4% vs. 16.6%, IRR   =   0.99, 95% CI, 0.91 to 1.07) compared to mothers of term children (N   =   24,932). Mothers of term children had a higher rate of any mental disorder in the first year while mothers of preterm children had higher rates from 2 to 5 years. Being the mother of a child born <28 week (IRR   =   1.5, 95% CI, 1.14 to 2.04), but not 28-33 weeks (IRR   =   1.03, 95% CI, 0.86 to 1.19) or 34-36 weeks (IRR   =   0.96, 95% CI, 0.88 to 1.05), was associated with any mental disorder.

INTERPRETATION

Mothers of preterm and term children had similar rates of incident mental disorders within 5-years post-delivery. Extreme prematurity was a risk factor for any mental disorder. Targeted screening and support of this latter group may be beneficial.

Investigating the relationship between melatonin patterns and methylation in circadian genes among day shift and night shift workers

OBJECTIVES

Mechanisms underlying the carcinogenicity of night shift work remain uncertain. One compelling yet understudied cancer mechanism may involve altered DNA methylation in circadian genes due to melatonin secretion patterns. The objective of this study was to explore the relationship between melatonin secretion patterns and circadian gene methylation among day and night shift workers.

METHODS

Female healthcare employees (n=38 day workers, n=36 night shift workers) for whom we had urinary 6-sulfatoxymelatonin secretion data from a previous study were recontacted. New blood samples were collected and used to measure methylation levels at 1150 CpG loci across 22 circadian genes using the Illumina Infinium MethylationEPIC beadchip. Linear regression was used to examine the association between melatonin (acrophase and mesor) and M values for each CpG site (false discovery rate, q=0.2), while testing for effect modification by shift work status.

RESULTS

Among night shift workers, a higher mesor (24 hours of mean production of melatonin) was associated with increased methylation in the body of RORA (q=0.02) and decreased methylation in the putative promoter region of MTNR1A (q=0.03). Later acrophase (ie, time of peak concentration) was associated with increased methylation in the putative promoter region of MTNR1A (q=0.20) and decreased methylation in the body of PER3 (q=0.20). No associations were identified among day workers.

CONCLUSIONS

In conclusion, patterns in melatonin secretion were associated with differential circadian gene methylation among night shift workers. Melatonin and alteration of DNA methylation in circadian genes may be one pathway towards increased cancer risk, although larger-scale studies examining multiple time points are needed.

DNA methylation of circadian genes and markers of cardiometabolic risk in female hospital workers: An exploratory study

Night shift work has been linked to increased risk of cardiovascular disease (CVD); however, the underlying mechanisms remain unclear. A compelling yet understudied mechanism involves differential DNA methylation of circadian genes. To investigate the relevance of this mechanism, we conducted an exploratory cross-sectional study of 74 female hospital personnel (38 day workers, 36 night shift workers). Sociodemographic, lifestyle, and health characteristics as well as shift work status and history were determined through self-report. Fasting blood samples were collected to measure markers of cardiometabolic risk and DNA was extracted to measure DNA methylation of 1150 cytosine-guanine (CpG) sites across 22 circadian genes. Associations between methylation levels at individual CpG sites (β-values) and markers of cardiometabolic risk were analyzed while considering effect modification by shift work status. The false discovery rate was applied to account for multiple comparisons (q ≤ 0.20). Two CpG sites [cg06758649 (CRY1) and cg06899802 (CSNK1A1)] were differentially associated with waist circumference and body mass index by shift work status, and eight CpG sites [cg26103512 (CSNK1D), cg03941313 (CSNK1E), cg18217763 (CSNK1E), cg16682686 (DEC1), cg12061096 (RORA), cg10133825 (RORA), cg19652148 (RORA), and cg22904654 (RORA)] were differentially associated with LDL cholesterol concentration by shift work status (all q ≤ 0.20). Our findings suggest that the relationship between DNA methylation of circadian genes and cardiometabolic risk differs by day and night shift worker status, which may contribute to mechanisms of increased risk of CVD observed among night shift workers.

Exploring the impact of night shift work on methylation of circadian genes

Night shift work is associated with increased breast cancer risk, but the molecular mechanisms are not well-understood. The objective of this study was to explore the relationship between night shift work parameters (current status, duration/years, and intensity) and methylation in circadian genes as a potential mechanism underlying the carcinogenic effects of night shift work. A cross-sectional study was conducted among 74 female healthcare employees (n = 38 day workers, n = 36 night shift workers). The Illumina Infinium MethylationEPIC beadchip was applied to DNA extracted from blood samples to measure methylation using a candidate gene approach at 1150 CpG loci across 22 circadian genes. Linear regression models were used to examine the association between night shift work parameters and continuous methylation measurements (β-values) for each CpG site. The false-discovery rate (q = 0.2) was used to account for multiple comparisons. Compared to day workers, current night shift workers demonstrated hypermethylation in the 5'UTR region of CSNK1E (q = 0.15). Individuals that worked night shifts for ≥10 years exhibited hypomethylation in the gene body of NR1D1 (q = 0.08) compared to those that worked <10 years. Hypermethylation in the gene body of ARNTL was also apparent in those who worked ≥3 consecutive night shifts a week (q = 0.18). These findings suggest that night shift work is associated with differential methylation in core circadian genes, including CSNK1E, NR1D1 and ARNTL. Future, larger-scale studies with long-term follow-up and detailed night shift work assessment are needed to confirm and expand on these findings.