A growing body of evidence linking increased night light to certain types of cancer has led researchers to suspect it could be connected to the steady increase in cases of childhood leukemia.

Scientists presenting research at the First International Scientific Conference on Childhood Leukemia on Wednesday said that light at night (LAN) and working shifts, which disrupts the body’s internal clock, have been associated with an raised risk of breast and colorectal cancer.

“We don’t know whether abnormal light exposure is generating this higher incidence of childhood leukemia or not, but in view of what we know of other forms of cancer this is not unreasonable,” Russell Foster, a molecular neuroscientist at Imperial College London, said in an interview.

“It is something we should look at and pay attention to.” Leukemia, the commonest cancer in young children, is thought to result from a mixture of genetic predisposition and environmental factors.

Ionizing radiation, electromagnetic fields, chemicals and viruses and infections have been implicated in the incidence of the illness, which has increased by about 50 percent in children under five years old since the 1950s.

“This is a potential environmental factor that we should take more seriously,” Foster said.

Professor Russel Reiter, of the University of Texas, said that compared to 100 years ago people are exposed to much more light at night, which disrupts the body’s circadian rhythms, or internal clock, and suppresses the normal nocturnal production of the hormone melatonin.

Studies have shown that a reduction in melatonin is linked to an increased risk of certain cancers.

“As an antioxidant, in many studies melatonin has been shown to protect DNA from oxidative damage. Once damaged, DNA may mutate and carcinogenesis may occur,” Reiter told the meeting.

Foster, who discovered a new type of light-sensing cell within the eye that provides information that regulates the circadian system, said there is a known link between the timing of anti-cancer drugs in children with leukemia and the risk of relapse.

“There is a big effect in giving the drug at the right time,” he told Reuters.

He also noted that genes and protein products that are associated with the circadian system also seem to interact closely with the cell cycle and the proliferation of cells.

Cancer develops when damaged cells duplicate uncontrollably and form tumors.

“The potential is there that when we disturb our circadian rhythms, when we suppress our melatonin, that increased cancer risk can result,” said Reiter.

“Misuse of light may be contributing to a number of different cancers including the increasing incidence of leukemia in children,” he added.