Mismatch of Sleep and Work Timing and Risk of Type 2 Diabetes.

OBJECTIVE: To examine whether a mismatch between chronotype (i.e., preferred sleep timing) and work schedule is associated with type 2 diabetes risk. RESEARCH DESIGN AND METHODS: In the Nurses' Health Study 2, we followed 64,615 women from 2005 to 2011. Newly developed type 2 diabetes was the outcome measure (n = 1,452). A question on diurnal preference ascertained chronotype in 2009; rotating night shift work exposure was assessed regularly since 1989. RESULTS: Compared with intermediate chronotypes, early chronotypes had a slightly decreased diabetes risk after multivariable adjustment (odds ratio 0.87 [95% CI 0.77-0.98]), whereas no significant association was observed for late chronotypes (1.04 [0.89-1.21]). Among early chronotypes, risk of type 2 diabetes was modestly reduced when working daytime schedules (0.81 [0.63-1.04]) and remained similarly reduced in women working <10 years of rotating night shifts (0.84 [0.72-0.98]). After ≥10 years of shift work exposure, early chronotypes had a nonsignificant elevated diabetes risk (1.15 [0.81-1.63], Ptrend = 0.014). By contrast, among late chronotypes, the significantly increased diabetes risk observed among day workers (1.51 [1.13-2.02]) appeared largely attenuated if their work schedules included night shifts (<10 years: 0.93 [0.76-1.13]; ≥10 years: 0.87 [0.56-1.34]; Ptrend = 0.14). The interaction between chronotype and shift work exposure was significant (Pinteraction = 0.0004). Analyses restricting to incident cases revealed similar patterns. CONCLUSIONS: In early chronotypes, type 2 diabetes risk increased with increasing duration of shift work exposure, whereas late types had the highest diabetes risk working daytime schedules. These data add to the growing body of evidence that workers could benefit from shift schedules minimizing interference with chronotype-dependent sleep timing.

The association of body size in early to mid-life with adult urinary 6-sulfatoxymelatonin levels among night shift health care workers.

BACKGROUND: Adult body mass index (BMI) has been associated with urinary melatonin levels in humans; however, whether earlier-life body size is associated with melatonin, particularly among night shift workers, remains unknown. METHODS: We evaluated associations of birth weight, body shape (or somatotype) at ages 5 and 10, BMI at age 18 and adulthood, weight change since age 18, waist circumference, waist to hip ratio, and height with creatinine-adjusted morning urinary melatonin (6-sulfatoxymelatonin, aMT6s) levels among 1,343 healthy women (aged 32-53 at urine collection, 1996-1999) in the Nurses' Health Study (NHS) II cohort. Using multivariable linear regression, we computed least-square mean aMT6s levels across categories of body size, and evaluated whether these associations were modified by night shift work. RESULTS: Adult BMI was inversely associated with aMT6s levels (mean aMT6s levels = 34 vs. 50 ng/mg creatinine, comparing adult BMI ≥ 30 vs. <20 kg/m(2); P trend < 0.0001); however, other measures of body size were not related to aMT6s levels after accounting for adult BMI. Night shifts worked prior to urine collection, whether recent or cumulatively over time, did not modify the association between adult BMI and aMT6s levels (e.g., P interaction = 0.72 for night shifts worked within two weeks of urine collection). CONCLUSIONS: Our results suggest that adult BMI, but not earlier measures of body size, is associated with urinary aMT6s levels in adulthood. These observations did not vary by night shift work status, and suggest that adult BMI may be an important mechanism by which melatonin levels are altered and subsequently influence chronic disease risk.

Antihypertensive medication use and incident breast cancer in women.

The purpose of this study was to evaluate whether antihypertensive medication use, including long-term use, is associated with increased breast cancer incidence in women. We studied 210,641 U.S. registered nurses participating in the Nurses' Health Study (NHS) and Nurses' Health Study II (NHS II). Information on antihypertensive medication use was collected on biennial questionnaires in both cohorts, and breast cancer cases were ascertained during this period. Multivariable-adjusted Cox proportional hazard models were used to estimate relative risks of invasive breast cancer over follow-up (1988-2012 in NHS, 1989-2011 in NHS II) across categories of overall antihypertensive medication use and use of specific classes (diuretics, beta blockers, calcium channel blockers, and angiotensin-converting enzyme inhibitors). During follow-up, 10,012 cases of invasive breast cancer developed (6718 cases in NHS and 3294 in the NHS II). Overall, current use of any antihypertensive medication was not associated with breast cancer risk compared with past/never use in NHS (multivariable-adjusted relative risk = 1.00, 95 % CI = 0.95-1.06) or NHS II (multivariable-adjusted relative risk = 0.94, 95 % CI = 0.86-1.03). Furthermore, no specific class of antihypertensive medication was consistently associated with breast cancer risk. Results were similar when we considered hypertensive women only, and when we evaluated consistency and duration of medication use over time. Overall, antihypertensive medication use was largely unrelated to the risk of invasive breast cancer among women in the NHS cohorts.