Does night shift work increase risk of breast cancer?

Night shift work for women appears to have little or no effect on breast cancer incidence, according to results of a new study published in the Journal of the National Cancer Institute. The findings are at odds with a World Health Organization review that found night shift work was particularly likely to increase the risk of breast cancer.

Researchers looked at 542,246 women in the Million Women Study, 22,559 women in EPIC-Oxford, and 251,045 women in UK Biobank who had answered questions on shift work and were followed for incident cancer. Heterogeneity was assessed using Cox regression, which yielded multivariable-adjusted breast cancer incidence rate ratios (RRs) and 95% confidence intervals (CIs).

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In the Million Women Study 673 women who reported night shift work developed breast cancer; 28 women who reported night shift work developed breast cancer in EPIC-Oxford; and 67 women who reported night shift work developed breast cancer in UK Biobank. The RRs for any versus no night shift work were 1.00 (95% CI = 0.92 to 1.08), 1.07 (95% CI = 0.71 to 1.62), and 0.78 (95% CI = 0.61 to 1.00). In the Million Women Study, the RR for 20 or more years of night shift work was 1.00 (95% CI = 0.81 to 1.23) and no statistically significant heterogeneity by breast cancer risk factors or sleep patterns was seen.

The researchers concluded that night shift work appears to have either very little or no effect on the incidence of breast cancer.

NEXT: How perinatal risk factors may increase risk of OCD

How perinatal risk factors may increase risk of OCD

A variety of perinatal factors may increase the risk of a child having obsessive compulsive disorder (OCD), independent of any familial confounder, according to results of a new study published in JAMA Psychiatry.

Researchers in Sweden included in their analysis data from all 2,421,284 singletons born from January 1973 to December 1996. The children were followed through December 2013. Of the 1,403,651 families in the cohort, 743,885 families had differently exposed siblings, of which 11,592 families had clusters of full siblings who were discordant for OCD. The researchers analyzed the data from January 2015 to September 2016. All perinatal data were collected using the Swedish Medical Birth Register, including information on maternal smoking during pregnancy, obstetric delivery, labor presentation, birth weight, birth weight in relation to gestational age, head circumference score, gestational age (for preterm birth), and 5-minute Apgar score.

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Of the entire cohort, 17,305 people were diagnosed with OCD. The average age at first diagnosis was 23.4 years. An association with increased risk of OCD remained, even after controlling for familial cofounders and measured covariates, for smoking 10 or more cigarettes during pregnancy (hazard ratio [HR], 1.27; 95% confidence interval [CI], 1.02-1.58), 5-minute Apgar consistent with fetal distress (HR, 1.50; 95% CI, 1.07-2.09), preterm birth (HR, 1.24; 95% CI, 1.07-1.43), birth weight 1501 to 2500 g (HR, 1.30; 95% CI, 1.05-1.62) and 2501 to 3500 g (HR, 1.08; 95% CI, 1.01-1.16), breech presentation (HR, 1.35; 95% CI, 1.06-1.71), being large for gestational age (HR, 1.23; 95% CI, 1.05-1.45), and delivery by cesarean (HR, 1.17; 95% CI, 1.01-1.34).

An inverse dose-response association indicated an increasingly higher risk of OCD in children who had shorter gestation or lower birth weight. In addition, the data indicated a dose-response association between increased OCD risk and the number of perinatal events, with HRs ranging from (95% CI, 1.07-1.15) for 1 event to 1.51 (95% CI, 1.18-1.94) for 5 or more events.

The researchers concluded that many perinatal risk factors are linked to a higher risk of OCD and these risk factors are independent of any shared familial confounders. They believe that this may indicate a causal pathway between the risk factors and OCD.