This summary table contains detailed information about research studies. Summary tables offer an informative look at the science behind many breast cancer guidelines and recommendations. However, they should be viewed with some caution. In order to read and interpret research tables successfully, it is important to understand some key concepts. Learn how to read a research table.
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Introduction: Women who routinely work overnight shifts (such as nurses and flight attendants) over many years may have a slightly increased risk of breast cancer. One possible reason is the exposure to light related to these types of jobs. Being exposed to light throughout the night affects some hormone functions in the body that may be related to breast cancer.
Learn more about light at night, shift work and breast cancer risk.
Learn about the strengths and weaknesses of different types of studies.
See how this risk factor compares with other risk factors for breast cancer.
Study selection criteria: Prospective cohort studies, nested case-control studies and case-control studies with at least 200 breast cancer cases and meta-analyses.
Table note: Relative risk above 1 indicates increased risk. Relative risk below 1 indicates decreased risk.
Study
|
Study Population
(number of participants)
|
Follow-up
(years)
|
Duration of Overnight Shift Work
|
Relative Risk of Breast Cancer in Women who Worked Overnight Shifts versus Women who Did Not,
RR (95% CI)
|
Prospective cohort studies
|
Nurses' Health Study [1]
|
78,562 postmenopausal women
(2,441 cases)
|
10
|
1-14 years*
vs.
never
|
1.08
(0.99-1.18)
|
| |
|
|
15-29 years*
vs.
never
|
1.08
(0.90-1.30)
|
| |
|
|
30 or more years* vs.
never
|
1.36
(1.04-1.78)
|
Nurses' Health Study II [2]
|
115,022
pre- and postmenopausal women
(1,352 cases)
|
12
|
1-9 years*
vs.
never
|
0.98
(0.87-1.10)
|
| |
|
|
10-19 years*
vs.
never
|
0.91
(0.72-1.16)
|
| |
|
|
20 or more years* vs.
never
|
1.79
(1.06-3.01)
|
Shanghai Women’s Health Study [3]
|
73,049
pre- and postmenopausal women
(717 cases)
|
9
|
14-25 years vs.
never
|
0.9
(0.7-1.1)
|
| |
|
|
More than 25 years vs.
never
|
1.0
(0.8-1.3)
|
Nested case-control studies
|
| |
Cases
|
Controls
|
|
|
|
Lie et al. [4,5]
|
699
|
895
|
|
1-11 years
vs.
never
|
1.2
(0.9-1.5)
|
| |
|
|
|
12 or more years
vs.
never
|
1.3
(0.9-1.8)
|
| |
537
|
2,143
|
|
1-14 years
vs.
never
|
0.95
(0.67-1.33)
|
| |
|
|
|
15-29 years
vs.
never
|
1.29
(0.82-2.02)
|
| |
|
|
|
30 or more years
vs.
never
|
2.21
(1.10-4.45)
|
Danish Nurses Association [6]
|
267
|
1,035
|
|
1-5 years
vs.
never
|
1.5
(0.99-2.5)
|
| |
|
|
|
5-10 years
vs.
never
|
2.3
(1.4-3.5)
|
| |
|
|
|
10-20 years
vs.
never
|
1.9
(1.1-2.8)
|
| |
|
|
|
20 or more years
vs.
never
|
2.1
(1.3-3.2)
|
Case-control studies
|
| |
Cases
|
Controls
|
|
|
|
Hansen [7]
|
7,035
|
7,035
|
|
At least one job for 6 months or more
vs.
other†
|
1.5
(1.3-1.7)
|
Pesch et al. [8]
|
857
|
892
|
|
10-19 years
vs.
never |
0.83
(0.27-2.60)
|
| |
|
|
|
20 or more years
vs.
never |
2.48
(0.62-9.99)
|
Davis et al. [9]
|
813
|
793
|
|
At least one job‡
vs.
never
|
1.6
(1.0-2.5)
|
O'Leary et al. [10]
|
576
|
585
|
|
At least one job‡
vs.
never
|
0.55
(0.32-0.94)
|
Meta-analyses
|
Megdal et al. [11]
|
13 studies
|
|
Any night shift work
vs.
never
|
1.48
(1.36-1.61)
|
* Rotating night shifts at least three nights a week per month.
† Comparison of women who worked in a job with at least 60 percent night work for at least 6 months versus other employed women.
‡ At least one job in the past 10 to 15 years that required an overnight shift.
References
- Schernhammer ES, Laden F, Speizer FE, et al. Rotating night shifts and risk of breast cancer in women participating in the Nurses' Health Study. J Natl Cancer Inst. 93(20):1563-8, 2001.
- Schernhammer ES, Kroenke CH, Laden F, Hankinson SE. Night work and risk of breast cancer. Epidemiology. 17(1):108-11, 2006.
- Pronk A, Ji BT, Shu XO, et al. Night-shift work and breast cancer risk in a cohort of Chinese women. Am J Epidemiol. 171(9):953-9, 2010.
- Lie JA, Kjuus H, Zienolddiny S, Haugen A, Stevens RG, Kjærheim K. Night work and breast cancer risk among Norwegian nurses: assessment by different exposure metrics. Am J Epidemiol. 173(11):1272-9, 2011.
- Lie JA, Roessink J, Kjærheim K. Breast cancer and night work among Norwegian nurses. Cancer Causes Control. 17(1):39-44, 2006.
- Hansen J, Stevens RG. Case-control study of shift-work and breast cancer risk in Danish nurses: Impact of shift systems. Eur J Cancer. 48(11):1722-9, 2012.
- Hansen J. Increased breast cancer risk among women who work predominantly at night. Epidemiology. 2001 Jan;12(1):74-7, 2001.
- Pesch B, Harth V, Rabstein S, Baisch C, et al. Night work and breast cancer - results from the German GENICA study. Scand J Work Environ Health. 36(2):134-41, 2010.
- Davis S, Mirick DK, Stevens RG. Night shift work, light at night, and risk of breast cancer. J Natl Cancer Inst. 93(20):1557-62, 2001.
- O'Leary ES, Schoenfeld ER, Stevens RG, et al. for the Electromagnetic Fields and Breast Cancer on Long Island Study Group. Shift work, light at night, and breast cancer on Long Island, New York. Am J Epidemiol. 164(4):358-66, 2006.
- Megdal SP, Kroenke CH, Laden F, Pukkala E, Schernhammer ES. Night work and breast cancer risk: a systematic review and meta-analysis. Eur J Cancer. 41(13):2023-32, 2005.
Updated 08/13/12
