Table 1 Characteristics of studies included in the systematic review

Bauer 2013 [40] 

US

Georgia

Comprehensive Cancer Registry

Case-cohort, 2000–2007

NA

34053/61129

Outdoor (nW/cm²/sr)

Satellite imagery for 1992–2007

constructed by the DMSP by averaging daily readings of the satellite sensors and removing cloud cover

T1: < 21 (10)

2000–3000

1.15–1.73

Ref 1.00

Race, tumor grade and stage, year of diagnosis, age at cancer diagnosis, MSA status, births per 1000 women aged 15–50, MSA population mobility, population over 16 in the labor force, and prevalence of cigarette smoking

T2: 21–40 (31)

1.06 (0.97–1.16)

T3: > 41 (48)

1.12 (1.04–1.20)

Clarke 2021 [24]

Denmark

Danish Nurse Cohort

Cohort

1993/1999–2012

745/16941

Outdoor (nW/cm²/sr)

Data on annual residential outdoor LAN was obtained from the DMSP. High dynamic range data were used (available in 1996, 1999, 2000, 2003, 2004, 2006, and 2010). Calculation of annual exposure estimates: comparability across years and satellites was ensured by using the Interannual calibration coefficients provided by NOAA

T1: 0.00–21.9

 < 2000

0.00–0.58

Ref 1.00

Age, calendar year, and entry at baseline, birth cohort, urbanicity, alcohol consumption, marital status, and night shift work, road traffic noise

T2: 22.0–65.7

1.09 (0.90–1.31)

T3: 65.8–446.4

0.97 (0.77–1.23)

Davis 2001 [46]

US

Cancer Surveillance System of the Fred Hutchinson Cancer Research Centre

Case–control, 1992–1995

NA

813/1606

Indoor

Subjects were asked to classify the typical bedroom ambient light level according to the following six levels of darkness: 1) t h e subject wore a m ask to keep out light; 2) she could not see her hand in front of her face; 3) she could see to the end of her b ed; 4) she could see across the room; 5) she could barely read; an d 6) she could read comfortably

Q1: 0

2000–3000

1.15–1.73

Ref 1.00

Matched by age. Adjusted for parity, family history of breast cancer, oral contraceptive use, and recent discontinued use of hormone replacement therapy

Q2: 0.00–0.4

1.00 (0.70–1.40)

Q3: 0.4–0.9

0.90 (0.60–1.20)

Q4: 0.9–2.9

1.00 (0.70–1.40)

Q5: > 2.9

1.00 (0.70–1.40)

Fritschi 2013 [47]

Western Australia

Western Australia Cancer Registry

Population-based case–control , 2009–2011

NA

1205/2994

Indoor

LAN assessed by asking women whether they could read easily at night at work (high exposure or could see but not well enough to read at work (medium exposure). Those women who did not fit either of these definitions, but had enough light to read in their bedroom when sleeping during the day were assigned low exposure

T1: lowest

2000–3000

1.15–1.73

Ref 1.00

Age

T2: medium

1.06 (0.82–1.37)

T3: highest

1.25 (0.98–1.59)

Garcia-Saenz 2018 [41 ]

Spain

MCC-Spain multicase-control study

Case-cohort, 2008–2013

NA

1219/2604

Outdoor

Evaluation through MSI highly linked to blue light spectrum and melatonin suppression action spectrum

T1: lowest

 > 3000

0.58–1.15

Ref 1.00

Age, center, educational level, socioeconomic status, UVI, BMI, tobacco, family history of breast cancer, chronotype, menopausal status, mutual adjustment for other light exposures

T2: medium

0.91 (0.62–1.32)

T3: highest

1.47 (1.00–2.17)

Indoor

Evaluated through the MCC-Spain questionnaire where it was defined as the level of light in the bedroom during sleeping time when the participants were at 40y of age or at the age of diagnosis or interview

Total darkness

Ref 1.00

Almost dark

0.73 (0.44–1.21)

Quite illuminated

0.77 (0.39–1.51)

Dim light

1.01 (0.60–1.69)

Hurley 2014 [43]

US

California Teachers’ cohort study

Cohort, 1995–2010

NA

106 731 (tot)

Outdoor (nW/cm²/sr)

Data derived from satellite imagery data obtained from the archive of the US DMSP Operational Linescan System, maintained by NOAA’s Earth Observation Group

Q1: 0–14.2 (7.1)

2000–3000

1.15–1.73

Ref 1.00

Age strata (1 year), race/birthplace, family history of breast cancer, age at menarche, pregnancy history, breastfeeding history, physical activity, BMI, alcohol consumption, menopausal status and hormone therapy use combination, smoking status, smoking pack-years, neighborhood socio-economic status, and urbanization

Q2: 14.3–26.4 (20.35)

1.05 (0.95–1.16)

Q3: 26.5–37.4 (31.95)

1.06 (0.95–1.17)

Q4: 37.5–53.3 (45.4)

1.05 (0.95–1.17)

Q5: 53.4–175.2 (114.3)

1.12 (1.00–1.26)

Indoor

Indicators were based on responses to the questions: “During the past year, have you used a bright light at night while sleeping at home?

Non-user

Ref 1.00

Light

1.17 (0.87–1.57)

Medium

0.99 (0.82–1.20)

Heavy

1.13 (0.84–1.52)

James 2017 [44]

US

Nurses’ Health Study II

Cohort, 1989–2013

NA

3549/109672

Outdoor (nW/cm²/sr)

DMSP Global Radiance Calibrated

Night-time Lights high-dynamic range data

Interannual calibration

coefficients were provided by NOAA to derive exposure estimates

Q1: 0.4–7.2 (4.3)

2000–3000

1.15–1.73

Ref 1.00

Stratified for age at follow-up and calendar year. Adjusted for benign breast disease history, family history of breast cancer, age at menarche, parity, and age at first birth, height, white race, BMI, BMI at 18, oral contraceptive use, mammography screening, menopausal status, smoking, status, alternative healthy eating index, physical activity, marital status, living alone, personal income, shift work after 1989, region, PM2.5, census-tract median home value, income, and population density

Q2: 6.3–15.9 (12.4)

1.05 (0.94–1.18)

Q3: 14.4–30.1 (22.9)

1.01 (0.90–1.13)

Q4: 26–53.3 (37.2)

1.08 (0.97–1.22)

Q5: 41.4–248.1 (64.0)

1.14 (1.01–1.29)

Johns 2018 [42]

UK

Generations Study

Case-cohort, 2003–2012

6.1 years (mean)

1775/105866

Indoor

Women were asked to report their level of exposure to LAN over the year prior to recruitment and at age 20 years, in the room in which they slept, in the categories; ‘light enough to read’; ‘light enough to see across the room, but not read’; ‘light enough to see your hand in front of you, but not to see across the room’; and ‘too dark to see your hand, or you wear a mask’

T1: low

 < 2000

0.00–0.58

Ref 1.00

Year of birth, history of benign breast disease, breast cancer in a first-degree relative, socioeconomic score, age at menarche, age at first birth, parity, duration of breastfeeding, oral contraceptive use, hormone replacement therapy use, menopausal status, and age at menopause where applicable, premenopausal, and postmenopausal BMI, alcohol consumption, smoking and physical activity level

T2: medium

1.00 (0.89–1.12)

T3: high

1.01 (0.88–1.15)

Keshet-Sitton 2016 [48]

Israel

Various Medical Centers in Tiberius

Case–control, 2010–2014

NA

95/278

Indoor

Sleep quality, falling asleep with TV on (turning the TV off before sleeping), sleeping with the TV on for most of the night, exposure to outdoor and indoor lighting in the sleeping habitat, use of bed lamps or room lamps for reading before retiring to sleep were variables that were part of the questionnaire. Answers were scaled from 1 to 5, where 1 was lowest and 5 highest

Reading with bed light illumination

 > 3000

1.15–1.73

0.82 (0.68–0.99)

Matched by age and residential area

Sleeping with closed shutters

0.81 (0.67–0.97)

Resides near strong ALAN sources

1.52 (1.1–2.12)

Kloog 2011 [49]

Northern Israel

Breast cancer in Norther Israel study

Case–control, 2000–2008

NA

794/1679

Indoor

Nighttime bedroom-light level was evaluated using a 4-point scale: from completely dark (score of 1) to strong light (score of 4). The exact wording of the question was as follows: “How do you define your nighttime bedroom-light level? “1” (completely dark), “2” (low light), “3” (average light), or “4” (very strong light—all lights switched on). Other LAN exposure-related questions included the availability of bedroom shutters and sleeping with the television left on. The answers to these questions were coded dichotomously, that is, yes or no

TV off while sleeping

 > 3000

1.15–1.73

Ref 1.00

Matched by age, location of primary clinic, and ethnicity. Adjusted for family history of cancer, parity, oral-contraceptive use, and hormone-replacement therapy

TV on while sleeping

0.91 (0.73–1.15)

Bedroom light (scoring 1 to 4)

1.22 (1.12–1.31)

Li 2010 [50]

US

NA

Case–control, NA

NA

363/719

Indoor

Questions targeted detailed information on the participants’ sleeping patterns and bedroom light environment in the 10 years prior to diagnosis (or reference date for controls). Questions on sleeping patterns and bedroom light environment included: (1) whether hours slept occurred during the daytime or at night; (2) whether the lights were kept on while sleeping; (3) the presence of streetlights, lighted signs, or any other exterior light which affected the sleeping area; (4) pulling a window shade or curtain while sleeping; (5) having radio, TV, and/or hall lighting on while sleeping, and (6) hours of sleep per day

Keeping light off while sleeping

2000–3000

1.15–1.73

NA

Age group, race, BMI, age at first menstrual period, family history of breast cancer, age at first full-term birth, months of lifetime breast feeding, cigarette smoking, and alcohol drinking

Keeping light on while sleeping

No streetlights, lighted signs, or any other exterior light outside sleeping area

Streetlights, lighted signs, or any other exterior light outside sleeping area

Clock radio, TV, hall light, etc. off while sleeping

Clock radio, TV, hall light, etc. on while sleeping

O' Leary 2006 [51]

US

Long Island Breast Cancer Study Project

Case–control, 1996–1997

NA

576/1161

Indoor

Residential light-at-night exposures were ascertained for the

5-year period prior to the reference date compared with the distant past. Questions covered sleep hours, frequency of turning on lights during sleep hours, and length of time the light was on

Q1

2000–3000

1.15–1.73

Ref 1.00

Age at reference date, parity, family history (defined as a mother, sister, or daughter with breast cancer), education (defined as less than high school or high school graduate as the referent vs. some college, college graduate, and post college education), and history of benign breast disease

Q2

0.98 (0.66–1.44)

Q3

0.71 (0.43–1.16)

Q4

0.99 (0.67–1.48)

Q5

1.12 (0.80–1.57)

Ritonja 2020 [52]

Canada

NA

Population-based case–control , 2005–2010

NA

844/1749

Outdoor DNB (nW/cm²/sr)

For DNB, 2012 was chosen because it was the earliest year for which these data are available. Sensitivity to light in the wavelength range 500–900 nm

T1: 0.00–22.07 (11.035)

 < 2000

0.00–0.58

Ref 1.00

Age, ethnicity, menopausal status, family history of breast cancer, age at menarche, BMI, household income, education, parity, and age at first birth, years of oral contraceptive use, age at first mammography screening, smoking status, night work status, average alcoholic drinks/week, average population density, and average neighborhood income

T2: 22.08–32.79 (27.435)

0.97 (0.75–1.26)

T3: 32.83–149.47 (91.15)

0.95 (0.70–1.27)

Outdoor DMSP (nW/c m²/sr)

The DM SP data are fro m the annual “ra diometrica lly calibrate d” product for 2010. Sensitivity to light in the wavel ength range 500–900 nm

T1: 0.00–123.05 (61.525)

Ref 1.00

T2: 123.10–194.62 (158.86)

1.05 (0.82–1.34)

T3: 194.75–628.56 (411.655)

0.83 (0.63–1.09)

White 2017 [45]

US and Puerto Rico

Sister Study

Cohort, 2003–2009

3 years

50533

Indoor

Women were asked detailed questions about any types of light present while sleeping, frequency of waking up at night, frequency of naps and sleep medication use

Q1: No light

2000–3000

1.15–1.73

Ref 1.00

Age, race, education, income, marital status, postmenopausal hormone use, use or oral contraceptives, alcohol consumption, age at menarche, parity, age at first birth, age at menopause, pack years of smoking and physical activity

Q2: Daylight

0.87 (0.66–1.15)

Q3: Nightlight

0.97 (0.87–1.08)

Q4: Light outside the room

1.01 (0.90–1.13)

Q5: Light/television in room

1.09 (0.93–1.26)

Xiao 2020 [23]

US

NIH-AARP Diet and Health study

Cohort, 1995–2005

16 years

186 981 (tot)

Outdoor (nW/cm²/sr)

DMSP Global Radiance Calibrated Night-time Lights high-dynamic range data

Q1: 2.4–6.3 (4.3)

2000–3000

1.15–1.73

NA

Age, state of residence, ethnic, education, marital status, breast cancer in first-degree relatives, age of menarche, age at first childbirth, contraceptive use, age at menopause, menopause hormonal therapy, smoking status, vigorous physical activity, alcohol consumption, number of breast biopsies, mammogram in the past 3 years, healthy eating index-2005, census tract median home value, poverty rate and population density

Q2: 10.8–16.1 (13.3)

Q3: 23–31 (26.9)

Q4: 40.6–51.5 (45.7)

Q5: 66.6–90.3 (76.6)

Xiao 2021 [25]

US

Southern Community Cohort Study

Cohor t

NA

1224/43 500

Outdoor (nW/cm²/sr)

U.S. Defense Meteorological Satellite Program’s Operational Linescan System with high-dynamic range data to avoid saturation in high-LAN areas

Q1: 0.8–1.7 (1.2)

2000–3000

1.15–1.73

Ref 1.00

Age, education, marital status, income, health insurance coverage, smoking, family history of breast or ovarian cancer among first-degree female relatives, mammogram, age at menarche, postmenopausal status, ever use of menopausal hormone therapy, average number of alcoholic drinks consumed per day, and population density and percentage of households living under the 2000 federal poverty line in the census tract

Q2: 3.8–9.1 (6.2)

0.98 (0.82–1.18)

Q3: 16.3–24.3 (20.3)

1.13 (0.93–1.36)

Q4: 32.3–39.5 (35.9)

1.01 (0.82–1.25)

Q5: 48.9–68.2 (55.6)

1.27 (1.00–1.60)

Yang 2019 [53]

China

Jiujiang breast cancer study

Population-based case–control , 2013–2016

NA

401/802

Indoor

Validated 17-item SFQ to comprehensively collect 5-year sleep habits before their BC diagnosis for cases and the most recent 5-year sleep habits for population controls. The SFQ includes eight subscales: habitual bedtim e information (four items), self-evaluation of sleep quality (one item), insomnia frequency (one item), history of sleep medication use (three items), LAN exposure (two items), frequency of nighttime waking (one item), nightshift work (four items), and habitual nap time (one item)

Level 1 (wore a mask to keep out light or could not see hand in front of face)

2000–3000

1.15–1.73

Ref 1.00

Age, education, family income, occupation, menopausal status, number of live births, use of menopausal hormones, age at menarche, age at first birth, marital status, family history of breast cancer, smoking, alcohol drinking, fruit and vegetable consumption, regular physical activity, BMI, and adjusted mutually for other sleep variables including sleep duration, sleep quality, light exposure at night, night/shift work, and sleep medication use

Level 2 (could see only the hazy outline of the bedroom)

1.08 (0.75–1.93)

Level 3 (could barely read)

1.1 (1.02–2.35)

Level 4 (could read comfortably)

1.19 (1.06–2.68)