Breast Cancer Risk Factors: Night Shift Work and Light at Night

Some studies show women who routinely work night shifts for many years have a small increased risk of breast cancer [252-255].

More research is needed to understand which aspects of shift work may be related to breast cancer risk.

One possible reason for the increased risk among these workers is their exposure to light at night.

For a summary of research studies on night shift work, light at night and breast cancer risk, visit the Breast Cancer Research Studies section.

Learn about other factors linked to the risk of breast cancer.

Light at night, melatonin and breast cancer

Melatonin is a hormone in the body that helps control the sleep cycle. During the night, the body makes melatonin. Exposure to light at night disrupts this process.

Findings on melatonin levels in the body and breast cancer risk are mixed [256-257].

However, some findings suggest women with lower levels of melatonin may have a greater risk of breast cancer than women with higher levels [257]. Exposure to light at night may be linked to an increased risk of breast cancer because it limits the production of melatonin.

Lower melatonin levels may also be linked to an increased production of estrogen [254]. High levels of estrogen in the body are linked to an increased risk of breast cancer [22].

These processes in the body and how they may be related to breast cancer risk among night shift workers are under study.

Learn more about estrogen and breast cancer risk.

Updated 04/23/24