How Light Affects Sleep and Biorythm
We all have a biological clock in our bodies which enables us to adjust ourselves to the cycle of brightness levels of the sunlight. It is commonly seen in many living creatures on earth. But since the invention of fluorescent lamp, humans have been spending bright nights. It may have brought some unexecpted impact on out biological clock and biorythm. While artificial light has been praized for the convenience it brings, it has also been reported recently that it can obstruct our sleep, make our bioryrthm nocturnal and even raise the risk of obesity and cancer. Are we properly adjusted to the natural lights that change dynamically by latitudes and seasons as well as artifitial lights that continuously illuminate us? The purpose of our studies is to clarity how light affects our health or biorythm.
Our Current Research Themes
- Study on Individual Difference in Photoreactive Property of Biorythm and its Causes
- Study on Photoreactive Property and Sleep of Children
- Functional Evaluation of Melanopsin Ganglion Cell of Human Retina
- Study on Melanopsin Polymorphism and Photoreactive Property of Human
- Integral Effect Evaluation of Mental and Physiological Effects of Light
Our Research Results
Influence of Night Computor Work on Sleep and Biorythm
- This study clarified that working on a brigh screen of computor at night suppression the secretion of hormon called melatonin which is secreted at night. It also clarified that such condiion hinders the natural nocturnal variation of body temperature, heart rate and brain activity.
Effects of VDT tasks with a bright display at night on melatonin, core temperature, heart rate, and sleepiness,J Appl Physiol,94(5): 1773-1776,2003.05. [PubMed] - This study clarified that sleeping right after such computor work as aforementioned above makes it harder to get asleep and influences sleep architecture (amount of REM sleep).
Effects of Playing a Computer Game Using a Bright Display on Pre-Sleep Physiological Variables, Sleep Latency, Slow Wave Sleep and REM Sleep,J Sleep Res,14(3): 267-273,2005.09. [PubMed]
Seasonal Variation of Human Biological Reaction to Light
- This study was conducted to examine the seasonal variation of photoreactive property based on the finding that the secretion of melatonin is suppressed by being exposed to light at night. As a result, it was proved that in winter, when daylight hours become shorter, the secretion of melatonin is more actively suppressed by light. This result is considered to be the biological reaction of human body adjusting to the lesser amount of daylight.
Less exposure to daily ambient light in winter increases sensitivity of melatonin to light suppression,Chronobiol Int,24 (1), 31-43,2007.01. [PubMed]
Ethnic Difference in Human Bioreaction to Light
- Why have people who moved their habitat to the high altitude areas in Europe acquired white skin? While the significance of skin color in temrs of adaptaion process was well known, the significance of iris pigmentation had not been clearly understood. This study showed that European ehtnic groups with light iris pigmentatin have realtively higher photoreactivity, which is indicated by the suppression of melatonin secretion, compared to Asian ethnic groups with dark iris pigmentation. Light iris pigmentation might have been an adaptive characteristic in terms of biorythm.
Influence of eye colors of Caucasians and Asians on suppression of nocturnal melatonin secretion by light,Am J Physiol Regul Integr Comp Physiol,292, R2352-2356,2007.06. [PubMed]