Working night shifts may increase the risk of developing ovarian cancer, a new study has warned.
Working night shifts was associated with a 24 per cent increased risk of advanced ovarian cancer and a 49 per cent increased risk of early stage disease compared with those who worked normal office hours, according to the research published in journal Occupational and Environmental Medicine.
The authors based their findings on 1101 women with the most common type (epithelial) of advanced ovarian cancer; 389 with borderline disease; and a comparison group of 1832 women without ovarian cancer.
The women, who were all aged between 35 and 74, were asked about the hours they worked, including whether they had ever worked night shifts.
The International Agency for Research on Cancer (IARC), a part of the World Health Organization, has classified shift work that disrupts the body's normal time clock (circadian rhythm) as a cancer causing agent.
Among the women with invasive cancer, around 1 in 4 (26.6 per cent; 293) had ever worked nights, compared with 1 in 3 (32.4 per cent; 126) of those with borderline disease and around 1 in 5 (22.5 per cent; 412) of the comparison group.
The stint of night shifts averaged between 2.7 and 3.5 years across all three groups of women, with jobs in healthcare, food preparation and service, and office and admin support the most common types of employment.
However, the risk for ovarian cancer may be lower for night types ("owls") than for morning types ("larks"), the findings suggest.
A greater proportion (27 per cent) of women who described themselves as "owls" had worked night shifts than women (20 per cent) who were "larks".
The risks of either advanced ovarian cancer were slightly higher (29 per cent) among "larks" than among "owls" (14 per cent), although this difference was not statistically significant. Findings were similar for borderline tumours - 57 per cent and 43 per cent for "larks" and "owls," respectively.
Only women aged 50 and above were significantly more likely to have ovarian cancer if they had worked nights.
The authors said their findings are consistent with, and of a similar magnitude, as those found for breast cancer, but pointed out that they did not find any cumulative risk for ovarian cancer the longer a woman had worked a night shift pattern.
One possible explanation could be linked to melatonin, a powerful hormone that is normally produced at night, but suppressed by ambient light, and which regulates reproductive hormones, particularly oestrogen.
Melatonin also scavenges harmful free radicals and boosts production of other antioxidants in the body.
