Another Reason to Keep it Dark at Night?

[Guest guest]

British Journal of Cancer (2004) 90, 941-943.

doi:10.1038/sj.bjc.6601626

Melatonin and cancer risk: does light at night compromise physiologic

cancer protection by lowering serum melatonin levels?

E S Schernhammer1,2 and K Schulmeister3

1Channing Laboratory, Department of Medicine, Brigham and Women's

Hospital and Harvard Medical School, 181 Longwood Avenue, Boston, MA

02115, USA

2Ludwig Boltzmann-Institute for Applied Cancer Research, KFJ-Spital,

Vienna, Austria

3ARC Seibersdorf research, Health Physics Division, Seibersdorf A-

2444, Austria

Correspondence to: Dr ES Schernhammer, Channing Laboratory,

Department of Medicine, Brigham and Women's Hospital and Harvard

Medical School, 181 Longwood Avenue, Boston, MA 02115, USA. E-mail:

eva.schernhammer@...

Received 9 October 2003; revised 3 December 2003; accepted 5 December

2003

The suprachiasmatic nuclei in the hypothalamus, one of the most

important physiological determinants of alertness and performance,

drive a circadian pacemaker in mammals, with an intrinsic period

averaging 24 h. Light is the primary stimulus to the disruption and

resetting of this pacemaker, which is expressed in changing melatonin

rhythms. Melatonin production in humans decreases when people are

exposed to light at night. Since melatonin shows potential oncostatic

action in a variety of tumours, it is possible that lowered serum

melatonin levels caused by exposure to light at night enhance the

general tumour development. Cancer is the second leading cause of

death in industrialised countries like the United States, where a

significant proportion of workers engage in shift work, making a

hypothesised relation between light exposure at night and cancer risk

relevant. Observational studies support an association between night

work and cancer risk. We hypothesise that the potential primary

culprit for this observed association is the lack of melatonin, a

cancer-protective agent whose production is severely diminished in

people exposed to light at night.

Keywords: melatonin; cancer; light exposure; night work