If work interferes with preferred sleep timing, one may be at higher risk of type 2 diabetes

Vetter C, Devore EE, Ramin CA, et al.
Diabetes Care published ahead of print June 24, 2015

Background

Both laboratory and observational studies have suggested a link between sleep and altered glucose metabolism. Not only sleep duration and quality may affect metabolic processes, but timing of sleep may also be critical [1]. Late chronotypes, those who fall asleep and wake up later, show higher HbA1c levels [2] and a higher risk for metabolic syndrome [3] and type 2 diabetes (T2DM) [4] than early or intermediate chronotypes.
Sleep timing is regulated by the circadian clock, but In modern day society also by work schedules. It has been shown that early chronotypes sleep worse and ls and that they display the largest circadian misalignment during night shift work. Early morning shifts disrupt the sleep and circadian system in late chronotypes [5]. This suggests an interaction between chronotype and working times, which may modulate sleep and ultimately health [6].
In experimental settings, it has been shown that greater circadian misalignment was associated with impaired glucose metabolism, decreased insulin sensitivity and lower leptin levels [7]. Imposing a combination of partial sleep deprivation and circadian misalignment in a laboratory setting yielded decreased metabolic rates and increased plasma glucose levels [8].
This study examines the association of chronotype with T2DM risk and how rotating night shift work may modulate these associations, in the Nurses’ Health Study 2 (NHS2). 35% of women classified themselves as early chronotypes, 54% as intermediate, and 11% as late.

Main results

• Among women who had never worked rotating night shifts, late chronotypes showed a significantly higher T2DM risk (multivariable OR (MVOR): 1.51, 95%CI: 1.13-2.02) vs. intermediate chronotypes. The reduced risk of early chronotypes was not significant.
• Among women with <10 years of rotating night shifts work experience, early chronotypes showed a lower risk (MVOR: 0.84, 95%CI: 0.72-0.98). Women with the late chronotype now showed an attenuated risk (MVOR: 0.93, 95%CI: 0.76-1.13).
• In women with >10 years of shift work exposure, none of the groups had an increased risk of T2DM as compared to the intermediate chronotype.
• A significant trend across shift work categories was seen in early (P(trend)=0.014) but not in late (P(trend)=0.14) chronotypes.
• A significant interaction between shift work exposure and chronotype was seen (X(1) =12.4, P(interaction) = 0.0004).
• The associations between chronotype and T2DM did not differ much between BMI strata (<25 and >25 kg/m2).

Conclusion

This cohort study examined the interaction between chronotype and shift work. These observations in women suggest a slightly lower risk of T2DM in early vs. intermediate chronotypes, when working during daytime. The risk seemed to increase with increasing duration of rotating night shift work. Late chronotypes, by contrast, showed an increased risk of T2DM when their shift schedule did not involve night work, but only if they did not have work experience with rotating night shifts. These findings suggest that shift and day workers may be at increased risk for T2DM when work times interfere with preferred sleep timing.

Find this article online at Diabetes Care

References

1. Larcher S, Benhamou PY, P´epin JL, Borel AL. Sleep habits and diabetes. Diabetes Metab. 23 January 2015 [Epub ahead of print]. DOI: 10.1016/j.diabet.2014.12.004
2. Reutrakul S, Hood MM, Crowley SJ, et al. Chronotype is independently associated with glycemic control in type 2 diabetes. Diabetes Care 2013;36:2523–2529
3. Wong PM, Roecklein KA, Muldoon M, Manuck S. Later chronotype is associated with increased risk for the metabolic syndrome (Abstract). Sleep 2013;36(Suppl.):A285
4. Merikanto I, Lahti T, Puolijoki H, et al. Associations of chronotype and sleep with cardiovascular diseases and type 2 diabetes. Chronobiol Int 2013;30:470–477
5. Juda M, Vetter C, Roenneberg T. Chronotype modulates sleep duration, sleep quality, and social jetlag in shift-workers. J Biol Rhythms 2013;28:141–151
6. Luyster FS, Strollo PJ Jr, Zee PC, Walsh JK; Boards of Directors of the American Academy of Sleep Medicine and the Sleep Research Society. Sleep: a health imperative. Sleep 2012;35:727–734
7. Scheer FAJL, Hilton MF, Mantzoros CS, Shea SA. Adverse metabolic and cardiovascular consequences of circadian misalignment. Proc Natl Acad Sci U S A 2009;106:4453–4458
8. Buxton OM, Cain SW, O’Connor SP, et al. Adverse metabolic consequences in humans of prolonged sleep restriction combined with circadian disruption. Sci Transl Med 2012;4: 129ra143