7578409636

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The New England

Journal of Medicine

^JCupyrijb*. IVM. I»y ilu: M:ivc:k-Iuinciis    StHk ijf

Vol«,mc 322    MAY 3, IWO    Ńumbcr Ul

EXPOSURETO BRIGHT LICHT AND DARKNESS TO TREAT PHYSIOLOCIC

MALADAPTATION TO NIGHT WORK

Charles A. Czeisler, Pii.D., M.D., Miciiael P. Johnson, A.B., Jeanne F. Duffy, Emery N. Brown, M.D., Pii.D., Joseph M. Ronda, M.S., ano Richard E. Kkonaucr, Pii.D.

Abstract Working at night results in a misalignment be-twecn the sleep-wake cyde and the output of the hypo-thalamic pacemaker that regulates the arcadian rhythms of cerlain physiologic and behaviora! variables. Wc cvału-ated whether such physiologic maladaptation to nighttime work coutd be .prcvented eftectivety by .a treatment regi-men of exposure to bright light during the night and dark-ness during the day. We assessed Ihe fundioning of the arcadian pacemaker in five control and five treatment studies in order to assess the extcnt of adaptation in eight normal young men to a week of night work.

In the control studies. on the sixih consecutivc night of sedentary work in ordinary light (approńmateły 150 lux), the mean (±SEM) nadir of the endogenous temperaturę cyde continued to occur during the night (at 03:31 ±056 hours), indicating a łąck of arcadian adaptation to the nighttime work Schedule. In oontrast, the subjeds in the treatment studies were exposed to bright light (7000 to 12.000 lux) at night and to nearfy complete darkness during the day. and the temperaturę nadir shifted after four days of treatment to a significantly later, midafternoon hour (1453±032; P<0.0001), indicating a successful rir-cadian adaptation to daytime sleep and nighttime work. There were concomitanl shifts in the 24-hour pattems of plasma cortisol concentration, urinary excrelion ratę. sub-jective assessment of alertness. and cognitive performance in the treatment studies. These shitts resulted in a significant improvement in both alertness and oognitive performance in the treatment group during the night-shift hours.

We condude that maladaptation of the human circadian system to night work, with its assodated decłine in alertness, performance, and quatity of daytime sleep. can be treated effectiveły with scheduled exposure to bright light at night and darkness during the day. (N Engl J Med 1990; 322:1253-9.)

A PPROXIMATELY 7.3 million Amcricans worl 1 \ at night, cithcr on permanent shifis or on schedy ules rcguirihg a rotation of day, cvening, and night' work.¹ These workers forgo noctumal slccp and then attempt to sleep during daylight hours. Yet, as Bene-dict first noted at ihe turn of the century, a complctc physiologic adaptation of endogenous circadian rhythms to such inversion of the daity routine docs not occur¹*⁴ even after ycars of permanent nighttime work.^5,6 Physiologic maladaptation to an inverted Schedule results in diminished alertness and performance during nighttime work, with attendant incrcases in the number of fatigue-rclatcd aeddents during nighttime hours.⁶*⁹ Then, despitc the nociurnal depri-

From (tic Center fot Circadian and Slccp Oitordcn Mcdicinc. Oiritwn of Endoc/inotogy. Ocpannicm of Mcdkine. I lanrard McdicaJ Srttool. Origham and Wooicn’s Iłotpiul. Oohoo (C.A.C..    J.F.D.. C.N.O.. I.M.K.); and Ihe

Oivis*on of Applied Sciences. łlarvard Univcni<y. Cambridęe. Mav. (R.C.K.). Addrtts reprint rcqvcsu hi Or. Cxc»>lcr ai the Center for Ćueadian and Slccp Disorderi Medicine. łlinrard Medicaf Schooł. Rrigham and Womca's lluipiial. 221 Longwood Avc.. IłoHon. MA 02115.

Suppurtod in pan by rcsearch and łoining grami (DRR-CCkC S MOI-KROOdłW. DKR-URS<; 2 S07 KK05V50. NIA-I K0I-AGO6GI2. NIMII-I RUI-Ml 145130. N1DDK-5-T32-OK-07529) kont the National Inonmciof Iłcahh. I.y tlrigłuat and WunwiTt Ilwpul, and by tbe Center Inr    «rf Induoriul

Sdcdutes. a mmprnAi wrvicc orgafli/Jrtioo di/cctcd by l)r. Creitlor.

vation of slccp, thcsc workers typtcally cxpcricncc daytime insomnia.^,<M4 Long-tcrm cxposurc to variablc work schcdulcs that inelude work at night is also asso-ciatcd with an inereased risk of cardiovascular dis-casc, gastrointcstinal illncss, rcproduc(ivc dysfunction in women, and slccp disorder.¹⁵*¹⁸ Improvcmcnts in performance and wcll-bcing have bccn achicvcd as a rcsult of modifications in work-schcdulc design,¹⁴ bul true physiologic adaptation to night work under field conditions has not previously bcen dćmonstrated.

During the past 20 years. considcrable progress has bcen madc in understanding the undcrlying ncuro-physiologic proccsscs tliat regulatc adaptation to tlić periodie aspects of che cxtcrnal cnvironmcnt. Studies invołving ablation, transpiantation, and otlicr procc-dures havc dćmonstrated that the suprachiasmatic nuclci of the hypothalamus scrvc as (lic principal pacemaker of the circadian timing system in mam-mals.^19-*¹ A spcctali/.cd rctinohypoihalamic tnict links the retina to these nuclci, forming a nonvisnal plioto-rccc|>livc system tliat mediates the syiichtoni/niion, or cniraitimciil, of the circadian pacemaker with *hc lighl-dark cyctc.^7/ Kvcn thouglt eorresjRinding strnctiircs suliserviug rhythmicity and plunie entruiu-