Graveyard shifts linked to cancer

The higher cancer rates don’t prove working overnight can cause cancer. There may be other factors common among graveyard shift workers that raise their risk for cancer.

However, scientists suspect that overnight work is dangerous because it disrupts the circadian rhythm, the body’s biological clock. The hormone melatonin, which can suppress tumor development, is normally produced at night.

If the graveyard shift theory eventually proves correct, millions of people worldwide could be affected. Experts estimate that nearly 20 per cent of the working population in developed countries work night shifts.

Among the first to spot the night shift-cancer connection was Richard Stevens, a cancer epidemiologist and professor at the University of Connecticut Health Center. In 1987, Stevens published a paper suggesting a link between light at night and breast cancer.

Back then, he was trying to figure out why breast cancer incidence suddenly shot up starting in the 1930s in industrialized societies, where night-time work was considered a hallmark of progress. Most scientists were bewildered by his proposal.

But in recent years, several studies have found that women working at night over many years were indeed more prone to breast cancer. Also, animals that have their light-dark schedules switched develop more cancerous tumors and die earlier.

Some research also suggests that men working at night may have a higher rate of prostate cancer.

Because these studies mostly focused on nurses and airline crews, bigger studies are needed to confirm or disprove the findings.

There are still plenty of skeptics. And to put the risk in perspective, the “probable carcinogen” tag means that the link between overnight work and cancer is merely plausible. Among the long list of agents that are listed as “known” carcinogens are alcoholic beverages and birth control pills. Such lists say nothing about exposure amount or length of time or how likely they are to cause cancer. The American Cancer Society website notes that carcinogens do not cause cancer at all times.

Still, many doubters of the night shift link may be won over by the IARC’s analysis to be published in the December issue of the journal Lancet Oncology.

“The indications are positive,” said Vincent Cogliano, who heads up the agency’s carcinogen classifications unit. “There was enough of a pattern in people who do shift work to recognize that there’s an increase in cancer, but we can’t rule out the possibility of other factors.”

Scientists believe having lower melatonin levels can raise the risk of developing cancer. Light shuts down melatonin production, so people working in artificial light at night may have lower melatonin levels. Melatonin can be taken as a supplement, but experts don’t recommend it long-term, since that could ruin the body’s ability to produce it naturally.

Sleep deprivation may be another factor in cancer risk. People who work at night are not usually able to completely reverse their day and night cycles.

“Night shift people tend to be day shift people who are trying to stay awake at night,” said Mark Rea, director of the Light Research Center at Rensselaer Polytechnic Institute in New York, who is not connected with the IARC analysis.

Not getting enough sleep makes your immune system vulnerable to attack, and less able to fight off potentially cancerous cells.

Confusing your body’s natural rhythm can also lead to a breakdown of other essential tasks. “Timing is very important,” Rea said. Certain processes like cell division and DNA repair happen at regular times.

Even worse than working an overnight shift is flipping between daytime and overnight work.

“The problem is re-setting your body’s clock,” said Aaron Blair, of the United States’ National Cancer Institute, who chaired IARC’s recent meeting on shift work. “If you worked at night and stayed on it, that would be less disruptive than constantly changing shifts.” Anyone whose light and dark schedule is often disrupted — including frequent long-haul travellers or insomniacs — could theoretically face the same increased cancer risk, Stevens said. He advises workers to sleep in a darkened room once they get off work. “The balance between light and dark is very important for your body. Just get a dark night’s sleep.”

Meanwhile, scientists are trying to come up with ways to reduce the risk. And some companies are experimenting with different lighting. So far, the color that seems to have the least effect on melatonin is one few would want: red.

TROUBLE IN BPO-LAND?

What does this news mean for India, where there is a sudden boom in the BPO sector and thousands of young people are working night shifts?

“There are no data as such in India for people who work night shifts,” says Dr Sameer Kaul, Oncologist at Indraprastha Apollo Hospitals, “but it is true that breast cancer is on the rise among young urban professionals who delay marriage and childbirth. The good news is that such researches are not always conclusive.”

But not everyone is optimistic.

“It is established that night shifts create havoc with the circadian rhythm and the hormone production – especially melatonin and cortisol,” says Dr H K Wangnoo, Consultant Endocrinologist, Indraprastha Apollo Hospital. “It compromises the immunity of the body, as the hormone melatonin has a role to play in propping up the immunity. Taken together with the other cancer-causing factors, the genetic trigger, environmental pollution and lifestyle issues especially obesity, it can be very possible.”

So what would be the way to handle this? Lifestyle changes, prescribes DR Wangnoo, “no junk food, exercise and work shifts of no more than six hours.”

Melatonin EXPLAINED

The hormone Melatonin is secreted by the pineal gland in the brain.

•Darkness stimulates the production of melatonin. Light suppresses its activity.

•Jet lag, shift work, poor vision can disrupt melatonin cycles. Some experts say exposure to low-frequency electromagnetic fields (common in household appliances) may disrupt melatonin production.

•Some researchers believe melatonin levels are related to the aging process. Young children have the highest levels of night-time melatonin and the levels diminish as we age.

Function

•It helps regulate other hormones and maintains the body’s circadian rhythm.

•Melatonin also helps control the timing and release of female reproductive hormones and regulates menstrual cycles

•In addition to hormonal activities, melatonin also has strong antioxidant effects. It also helps strengthen the immune system.

USE

•Melatonin supplements are used to control insomnia, jet lag, poor circadian rhythms, osteoporosis (it stimulates growth of o teoblast cells, which promote bone-growth), breast and prostate cancer.