There are two kinds of people in this world, one is eager to jump out of bed at dawn, full of energy into the day’s work, we call them “lark”; and another kind of people are waking up at dawn, at night will be alive and well, inspiration and creativity are bursting at this time, we compare this kind of people to “owls”. A recent study published in the journal Occupational and Environmental Medicine suggests that night shifts may increase the risk of ovarian cancer. At the same time, “larks” have a higher risk of ovarian cancer than “owls”. The International Agency for Research on Cancer (IARC) has long determined that night shifts disrupt the body’s normal biological clock (circadian rhythm) and are a strong cancer-causing factor. This study included 1101 female patients with common advanced epithelial cell ovarian cancer, another 389 with junctional tumors, and 1823 healthy women as controls. The mean age ranged from 35-47 years and the hours of work as well as the history of night shifts were recorded. The results of the study found that about one quarter (26.6%, 293) of the women in the invasive tumor group and one third (32.4%, 126) of the women in the junctional tumor group had a history of night work, while the same was true for only one fifth (22.5%, 412) of the control group. Women with ovarian cancer had lower contraceptive use and fewer births compared to the control group. This also confirms that contraceptive pills and motherhood are known factors that reduce the risk of ovarian cancer. In addition, the three groups had an average night shift of 2.7 to 3.5 years, mainly in the healthcare industry, food service industry, and office and administrative support industry. Night shifts increased tumor risk by 24% for late stage tumors and 49% for early stage tumors compared to the 9 to 5 group. The percentage of “owls” in the night shift population was 27%, surpassing the 20% percentage of “larks”. However, the risk of advanced ovarian cancer was higher among “larks” at 29% and “owls” at 14%, but there was no statistical difference. For junctional tumors, the results for “larks” and “owls” were very similar, at 57% and 43%. Meanwhile, only women over the age of 50 who developed ovarian cancer were affected by night work. This finding is consistent with breast cancer research, but this study did not find an increased cumulative risk of ovarian cancer with increased night work hours. The researchers believe that melatonin may be the main cause. Melatonin is released at night and regulates sex hormones, especially estrogen. Melatonin also scavenges harmful free radicals and promotes the production of other antioxidants in the body. But light stimulation at night inhibits melatonin release, which may be a major reason why working at night raises the risk of ovarian cancer.