Lighting for the human circadian clock: recent research indicates that lighting has become a public health issue
Section snippets
Summary
Studies now indirectly link exposures of shift workers to light at night (LAN) and higher incidences of breast cancer and colorectal cancers. One possible mechanism is melatonin (MLT) suppression by shift worker eye exposures to LAN. The pineal gland hormone MLT is normally produced at highest levels in the early morning hours, but is suppressed by open eye exposure to LAN. Rat studies by David E. Blask and colleagues show that MLT acts as a protective oncostatic agent that suppresses growth
Light and the evolution of the circadian clock
Since we are born into a world of artificial lighting, we do not give much thought to how light disrupts the normal 24 h circadian rhythms present in all organisms. Biological clock rhythms are found in all living things, even in organisms as simple as algae [59], [60], [61], [62]. Clock genes that time cellular functions were likely inherited from the Earth's first simple organisms over 4 billion years ago. The circadian clock is dependent upon dark nights that allow normal MLT production
Light pollution
Light pollution is produced by the use of ever brighter outdoor night lighting that is often used for the advertising of gas stations, convenience stores, and shopping centers. It is often justified in the name of “security”. Since the 1960s we have seen the increased outdoor use of HID lamps.
Light pollution is light that is not targeted for a specific task, is bright and uncomfortable to the human eye, causes unsafe glare to drivers and pedestrians, harms the biological integrity of
Receptor cell discovery
In year 2002, Brown University neuroscientist David M. Berson discovered a previously unknown function for retinal ganglion cells (RGC) [7]. Previously unknown connections and functions of a small population of RGC located in the base of the retina of rats were identified. Berson demonstrated that RGC axons connect to the circadian or biological clock center – the paired suprachiasmatic nuclei (SCN) – located within the hypothalamus at the base of the brain. The retinal-circadian light
Blue light photopigment
Melanopsin, a blue light sensitive photopigment, resides within the small population of RGC [42], [49]. The RGC are located deep in the retina of the eye beneath the rods and cones. These specialized cells are non-visual photoreceptors previously thought to only relay to the brain nerve impulses initiated by light striking the rods and cones. The RGC and their dendrites fire maximally when stimulated by blue light at wavelengths between 464 and 484 nm [7]. By comparison, the visual system of
Light at night, shift workers, breast cancer and colorectal cancer
Because, much of the daytime work force in the industrialized world is exposed to dim office lighting instead of bright sunlight, and because at night we are often exposed to bright lights with blue wavelengths instead of natural darkness, some researchers believe that adequate human circadian entrainment does not take place [58], [74]. Without a normal cycle of MLT inhibition and production responding to cycles of light and dark, human health may be negatively affected [5], [22], [25], [29],
Melatonin regulates and protects
MLT is a hormone that has sleep-inducing properties and regulates a balanced physiological state in humans [59], [60], [61]. MLT also has substantial free radical scavenging/antioxidant and anticancer activity in experimental systems [45], [60], [61], [63]. This knowledge has obvious relevance to human health [22], [26], [54], [60], [61], [66], [79].
The production and suppression of MLT is a circadian driven event. MLT is synthesized by the pineal gland, a pea sized gland located in the center
How much, how long, and what color?
MLT suppression by LAN will depend on the color of the light, its intensity, and the duration of the exposure of the eyes (both opened and closed) to the light source. A study by Hatonen et al. [43] found that only two of eight human subjects exposed to 2000 lx of white light for 60 min with eyes closed between midnight and 2:00 AM showed lowered MLT levels. The authors doubt that people sleeping with eyes closed in urban environments would have suppression of MLT. Typical room illuminations
The “precautionary principle”
The implications of these findings are that perhaps the “precautionary principle” should be applied in lighting applications. Carlin wrote:
The precautionary principle is no longer just a theory. Writing in Scientific American, David Appell notes how the precautionary principle is increasingly finding its way into international agreements [4]. He noted for example, that while it is already `a matter of law in Germany and Sweden, the precautionary principle may soon guide the policy of all of
Better lighting practices should begin now
Until more research directly links exposure to LAN to increased rates of human cancers, it may be wise to consider preventive measures in the application of everyday lighting practices.
The best way to daily entrain (reset) our circadian clocks and have our bodies produce a healthy dose of vitamin D is to get 15 min of natural sunlight exposure each morning [44]. At night we should sleep in total darkness. But in modern industrialized societies we see people with poor sleep habits. There are a
Conclusion
Lighting only for visual acuity or to achieve decorative effects is no longer acceptable [58]. Lighting must also be friendly to the circadian clock. We must recognize the body's need to sleep in darkness which allows for the normal night time production of MLT. MLT is a long-evolved protective hormone that should be allowed full expression during early morning hours.
On the basis of the growing body of animal research and human epidemiological studies the hypothesis that exposure to LAN may in
Acknowledgements
I wish to acknowledge the Lighting Research Office (LRO), a service of the Electric Power Research Institute, Palo Alto, CA, for holding their meeting on Light and Human Health in Orlando, FL, November 3–5, 2002. Neither the LRO nor the Electric Power Research Institute expressly endorses the ideas and content of this paper.
The Expedition Inspiration Fund For Breast Cancer Research and the late Laura Steele Evans who inspired thousands of breast cancer survivors were motivators for this paper.
References (79)
- et al.
Melatonin and colon carcinogenesis. III. Effect of melatonin on proliferative activity and apoptosis in colon mucosa and colon tumors induced by 1,2-dimethylhydrazine in rats
Exp. Toxicol. Pathol.
(2000) Strange vision: ganglion cells as circadian photoreceptors
Trends Neurosci.
(2003)- et al.
The effect of different light intensities on pineal melatonin content
Brain Res.
(1982) - et al.
Dose–response relationship between light irradiance and the suppression of plasma melatonin in human volunteers
Brain Res.
(1988) - et al.
The influence of different light spectra on the suppression of pineal melatonin content in the Syrian hamster
Brain Res.
(1984) - et al.
Breast cancer, blindness and melatonin
Eur. J. Cancer
(1992) - et al.
Melatonin and mammary pathological growth
Front. Neuroendocrinol.
(2000) - et al.
Effects of illumination on human nocturnal serum melatonin levels and performance
Physiol. Behav.
(1993) - et al.
Does winter darkness in the Artic protect against cancer? The melatonin hypothesis revisited
Med. Hypotheses
(1999) - et al.
Suppresson of melatonin by 2000-lx light in humans with closed eyes
Biol. Psychiat.
(1999)
Anticarcinogenic actions of melatonin which involve antioxidative processes: comparison with other antioxidants
Int. J. Biochem. Cell. Biol.
Melatonin: clinical relevance
Best Pract. Res. Clin. Endocrinol. Metab.
Melatonin inhibits fatty acid transport in inguinal fat pads of hepatoma 7288CTC-bearing and normal Buffalo rats via receptor-mediated signal transduction
Life Sci.
Polyunsaturated fatty acids, melatonin, and cancer prevention
Biochem. Pharmacol.
Effects of green or white light for treatment of seasonal depression
Psychiat. Res.
Light, endocrine systems and cancer – a meeting report
Neuroendocrinol. Lett.
Melatonin and colon carcinogenesis. I. Inhibitory effect of melatonin on development of intestinal tumors induced by 1,2-dimethylhydrazine in rats
Carcinogenesis
The new uncertainty principle
Melatonin, circadian rhythms, and sleep
New Engl. J. Med.
Phototransduction by retinal ganglion cells that set the circadian clock
Science
Growth and fatty acid metabolism of human breast cancer (MCF-7) xenografts in nude rats: impact of constant light-induced nocturnal melatonin suppression
Breast Cancer Res. Tr.
Melatonin inhibition of cancer growth in vivo involves suppression of tumor fatty acid metabolism via melatonin receptor-mediated signal transduction events
Cancer Res.
Light during darkness, melatonin suppression and cancer progression
Neuroendocrinol. Lett.
Melatonin as a chronobiotic/anticancer agent: cellular, biochemical, and molecular mechanisms of action and their implications for circadian-based cancer therapy
Curr. Top. Med. Chem.
Human melatonin regulation is not mediated by the three cone photopic visual system
J. Clin. Endocrinol. Metab.
Photic regulation of melatonin in humans: ocular and neural signal transduction
J. Biol. Rhythm.
Action spectrum for melatonin regulation in humans: evidence for a novel circadian photoreceptor
J. Neurosci.
Pineal research: the decade of transformation
J. Neural Transm.-Suppl.
Prospects of the clinical utilization of melatonin
Biol. Signal. Recept.
Melatonin, experimental basis for a possible application in breast cancer prevention and treatment
Histol. Histopathol.
Night-shift work, light at night, and risk of breast cancer
J. Natl. Cancer Inst.
Differential expression of high-affinity melatonin receptors (MT1) in normal and malignant human breast tissue
Am. J. Clin. Pathol.
Does light cause internal cancers? The problem and challenge of an ubiquitous exposure
Neuroendocrinol. Lett.
Light, melatonin and internal cancers – recent facts and research perspectives
Gesundheitswesen
Plasma melatonin in patients with breast cancer
Oncology
Cited by (321)
Louver configuration comparison in three Canadian cities utilizing NSGA-II
2023, Building and Environment