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Richard G. Stevens, Ph.D. - University of Connecticut. Farmington, CT, US

Richard G. Stevens, Ph.D. Richard G. Stevens, Ph.D.

Professor, Community Medicine and Health Care | University of Connecticut


Professor Stevens researches the health impact of artificial light pollution


I have been working for a long time trying to help figure out why people get cancer. One of my major interests has been in the possible role of iron overload. Largely on the basis of this work, published in the Journal of National Cancer Institute and the New England Journal of Medicine, the Swedish food industry decided to cease iron fortification of flour in the early 1990s.

Also, a perplexing challenge, which I had begun to engage in the late 1970s, is the confounding mystery of why breast cancer risk rises so dramatically as societies industrialize. In 1987, I proposed a radical new theory that use of electric lighting, resulting in lighted nights, might produce "circadian disruption" causing changes in the hormones relevant to breast cancer risk. Accumulating evidence has generally supported the idea, and it has received wide scientific and public attention. For example, my work on this has been featured on the covers of the popular weekly Science News several times (first on October 17, 1998) and the scientific journal Cancer Research (July 15, 1996). Since then, media interactions have been too numerous to list. Public outreach is important because it is "communcation of science to the people who pay for it".

Areas of Expertise (4)

Circadian Rhythms Health Impacts of Artificial Light Pollution Clinical Epidemiology Circadian Disruption

Education (2)

University of Washington: Ph.D., Epidemiology

University of California: B.S., Genetics

Affiliations (2)

  • Human Investigation Committee, DOH, State of Connecticut,
  • Medical Advisory Board, Young Survival Coalition







Media Appearances (5)

Harvard Study Strengthens Link Between Breast Cancer Risk and Light Exposure at Night

The Conversation  


A new study from Harvard has found greater risk of breast cancer in women who live in neighborhoods that have higher levels of outdoor light during the night.

The findings are based on the Nurses’ Health Study (NHS), which has for decades been advancing our understanding of risks to women’s health...

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Is Blue Light Bad For Your Health?



“As opposed to the many other kinds of harmful environmental pollutants out there, we are rapidly figuring out exactly what to do about this one, and it is really not that hard,” says Richard Stevens, PhD, a University of Connecticut cancer epidemiologist and light-at-night researcher. Just dim the lights at night and tone down that blue, he says...

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The Darkest Town In America



All those lights could have effects that ripple far beyond bedtime, but this is where the science gets more complicated. We know that older, nonelectric light isn’t that bad for us, said Richard Stevens, a professor in the School of Medicine at the University of Connecticut. But what of the new variety? “We evolved for billions of years as life on the planet with the reliable cycle of bright sunlight and dark,” Stevens said. “Humans figured out fire a long time ago, and we started making candles about 5,000 years ago, but that kind of light does not affect our physiology much at all.”...

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How the Street Light Has Been Given a Hi-tech Makeover



"Cool it and dim it" was how Dr Richard Stevens from the School of Medicine at the University of Connecticut summed up the AMA's recommendations.

In response, supporters argue that advances in technology in the last two or three years means that the bulbs are now softer and warmer in tone...

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Bright Light Accelerates Ageing in Mice



The analysis takes an innovative approach to studying circadian biology in mice, says Richard Stevens, an epidemiologist at the University of Connecticut School of Medicine in Farmington who studies the effect of light on cancer. But he says that the findings may not apply to people. The bright lights foisted on the mice were more dramatic than the light–dark cycles that people would experience in real life, even in extreme situations...

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Event Appearances (1)

Meeting report: the role of environmental lighting and circadian disruption in cancer and other diseases

Environmental health perspectives 2007 Sep  Stevens, Richard G; Blask, David E; Brainard, George C; Hansen, Johnni; Lockley, Steven W; Provencio, Ignacio; Rea, Mark S; Reinlib Leslie

Articles (5)

Light at night and breast cancer incidence in Connecticut: An ecological study of age group effects Science of the Total Environment

Portnov BA, Stevens RG, Samociuk H, Wakefield D, Gregorio DI.


The aim of this study was to test the prediction that within the state of Connecticut, USA, communities with high nighttime outdoor light level would have higher breast cancer incidence rates. Breast cancer cases were identified from the Connecticut Tumor Registry, the oldest within the United States, for years 2005 and 2009 and geocoded to the 829 census tracts in the state. Nighttime light level (LAN) was obtained from the Defense Meteorological Satellite Program (DMSP), 1996/97 satellite image, providing a 10-year lag. Regression models were used incorporating the LAN levels and census level data on potential confounders for the whole female population of the state, and for separate age groups. Light level emerged as a significant predictor of breast cancer incidence. After taking account of several potential confounders, the excess risk in the highest LAN level census tracts compared to the lowest was about 63% (RR=1.63; 95% CI=1.41, 1.89). The association of LAN with breast cancer incidence weakened with age; the association was strongest among premenopausal women.

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Circadian disruption and health: Shift work as a harbinger of the toll taken by electric lighting Chronobiology International

Stevens RG


Electric light is one of the signature inventions of human beings. A problem, however, is that electric light can confuse our endogenous circadian rhythmicity. It has now become apparent that circadian biology is fundamental to the functioning and adaptation of almost all life forms. In the modern world, everyone is exposed to electric light during the day and night, and thereby can experience some level of circadian disruption. Perhaps as a canary in the coal mine, study of people whose work hours include nighttime (shift workers) is beginning to yield insights on the adverse health effects of circadian disruption from electric light.

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Mortality risk from comorbidities independent of triple-negative breast cancer status: NCI-SEER-based cohort analysis Cancer Causes and Control

Swede H, Sarwar A, Magge A, Braithwaite D, Cook LS, Gregorio DI, Jones BA, R Hoag J, Gonsalves L, L Salner A, Zarfos K, Andemariam B, Stevens RG, G Dugan A, Pensa M, A Brockmeyer J.


A comparatively high prevalence of comorbidities among African-American/Blacks (AA/B) has been implicated in disparate survival in breast cancer. There is a scarcity of data, however, if this effect persists when accounting for the adverse triple-negative breast cancer (TNBC) subtype which occurs at threefold the rate in AA/B compared to white breast cancer patients.

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Circadian Modulation of 8-Oxoguanine DNA Damage Repair Scientific Reports

Manzella N, Bracci M, Strafella E, Staffolani S, Ciarapica V, Copertaro A, Rapisarda V, Ledda C, Amati M, Valentino M, Tomasetti M, Stevens RG, Santarelli L.


The DNA base excision repair pathway is the main system involved in the removal of oxidative damage to DNA such as 8-Oxoguanine (8-oxoG) primarily via the 8-Oxoguanine DNA glycosylase (OGG1). Our goal was to investigate whether the repair of 8-oxoG DNA damage follow a circadian rhythm. In a group of 15 healthy volunteers, we found a daily variation of Ogg1 expression and activity with higher levels in the morning compared to the evening hours. Consistent with this, we also found lower levels of 8-oxoG in morning hours compared to those in the evening hours. Lymphocytes exposed to oxidative damage to DNA at 8:00 AM display lower accumulation of 8-oxoG than lymphocytes exposed at 8:00 PM. Furthermore, altered levels of Ogg1 expression were also observed in a group of shift workers experiencing a deregulation of circadian clock genes compared to a control group. Moreover, BMAL1 knockdown fibroblasts with a deregulated molecular clock showed an abolishment of circadian variation of Ogg1 expression and an increase of OGG1 activity. Our results suggest that the circadian modulation of 8-oxoG DNA damage repair, according to a variation of Ogg1 expression, could render humans less susceptible to accumulate 8-oxoG DNA damage in the morning hours.

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Electric light, particularly at night, disrupts human circadian rhythmicity: is that a problem? Philosophical Transactions of the Royal Society


Over the past 3 billion years, an endogenous circadian rhythmicity has developed in almost all life forms in which daily oscillations in physiology occur. This allows for anticipation of sunrise and sunset. This physiological rhythmicity is kept at precisely 24 h by the daily cycle of sunlight and dark. However, since the introduction of electric lighting, there has been inadequate light during the day inside buildings for a robust resetting of the human endogenous circadian rhythmicity, and too much light at night for a true dark to be detected; this results in circadian disruption and alters sleep/wake cycle, core body temperature, hormone regulation and release, and patterns of gene expression throughout the body. The question is the extent to which circadian disruption compromises human health, and can account for a portion of the modern pandemics of breast and prostate cancers, obesity, diabetes and depression. As societies modernize (i.e. electrify) these conditions increase in prevalence. There are a number of promising leads on putative mechanisms, and epidemiological findings supporting an aetiologic role for electric lighting in disease causation. These include melatonin suppression, circadian gene expression, and connection of circadian rhythmicity to metabolism in part affected by haem iron intake and distribution.