Night shift work linked to cancer risk

A study by a team of international scientists has found that shift work may increase a person's risk of cancer.

The team of 44 scientists from 10 countries conducted the study at the request of the World Health Organization's (WHO) International Agency on Cancer Research (IARC) and say they found "limited" evidences of a link between cancer and people who work night shifts.

The team suggests that night shift work might raise the risk of cancer by suppressing production of melatonin, a hormone chemical involved in the circadian rhythm which are regular changes in mental and physical characteristics that occur in the course of a day.

They say there was a higher rate of breast cancer in female nurses who worked night shifts.

The study also reviewed research in which animals were exposed to light at night, disrupting the animals' circadian rhythm and found sufficient evidence of a connection between circadian rhythm disruption and cancer.

Researcher Dr. Kurt Straif, who works for the IARC in France, says shift work that involves circadian rhythm disruption is probably carcinogenic to humans.

The researchers also say that some work is worse for the health than others; people working as painters are carcinogenic, and those who work as firefighters are 'possibly carcinogenic' because of the on-the-job chemical exposure they experience.

They also say the studies were observational and do not prove cause and effect and many genetic and environmental factors affect cancer risk.

The research is published in the journal 'The Lancet'.