This study was extracted from a large study done on a population of 115,022 women without cancer at the start of the study. Of these women, 1,352 developed invasive breast cancer during the next 12 years of study. Those who had over 20 years of night rotating shifts had higher rates of breast cancer than those who did no night rotations or those who reported only a few years of night rotations.
It might be noted that the women who did over 20 years of night shifts were older and had higher rates of smoking. These factors could change cancer rates.
CONCLUSION: The authors encourage further studies of the connection of night time light exposure to levels of melatonin. Melatonin has proven cancer suppressing properties.