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In this Nov. 23, 2010 file photo released by CBS, host David Letterman smiles on the set of "The Late Show with David Letterman, in New York. (AP Photo/CBS, John Paul Filo) In this Nov. 23, 2010 file photo released by CBS, host David Letterman smiles on the set of "The Late Show with David Letterman, in New York. (AP Photo/CBS, John Paul Filo)  

Working the night shift may be deemed to cause cancer

Who knew that working the night shift could cause cancer?

“Shift work involving light at night” is among of the nominations for next year’s Report on Carcinogens released biennially by the National Toxicology Program. This means that working the night shift could be listed as a cancer-causing activity if it is ultimately included in the next report.

Besides working night shifts under light, other substances nominated for the next RoC include unleaded uranium, diesel exhaust particles and the human immunodeficiency virus, better known as HIV.

Shift work is described by the NTP as work with “with irregular, odd, flexible, variable, unusual, non-standard working hours” and is common in the health care, transportation, communication, leisure and hospitality sectors.

Public comments show there is actually concern that exposure to light at night may be carcinogenic in and of itself.

One public comment said that “evidence is mounting for the whole chain of causality ‐-‐ exposure to light at night, leading to reduced production of the hormone melatonin, leading to an increased rate of cancer.”

However, the comment added that no direct carcinogenic effect has been found in shiftwork itself, and it was only listed as a “probable carcinogen” by the International Agency for Research on Cancer in 2007.

Another public commentator said that “concerns exist for exposure to [light at night] in sleeping areas. This may come in the form of leaving bedroom lights on, leaving the TV on, to mandatory lighting in a barracks or institution.”

The Report on Carcinogens is a congressionally mandated biennial report on substances that may put people at an increased risk of cancer. The report is not a regulatory document, but state and federal regulators use the report as a guide.

“While the NTP argues that the RoC is not a regulatory document there is no question that it can be used to impact many regulations at the federal, state, and local level including workplace exposure limits, air permitting, and occupational safety guidelines among others,” M.J. Carrabba of the American Composites Manufacturers Association said in an email.

After a lengthy review process, a substance that is nominated can be labeled as a “known” or “reasonably anticipated” carcinogen.

However, critics charge that the RoC has serious flaws and that the RoC doesn’t explain the risk that a substance poses to human health, nor the level of exposure required for it to be carcinogenic.

“A listing in the National Toxicology Program’s (NTP) Report on Carcinogens (RoC) does not mean that a chemical presents any risk to human health at typical exposure levels,” David Fischer, senior director at the American Chemistry Council, told The Daily Caller News Foundation.

“We need to address the significant problems with the RoC,” added Fischer. “For example, when NTP listed formaldehyde in its 12th RoC we were disappointed it ignored the independent, peer-review report from the National Research Council of the National Academies, which strongly questioned whether the scientific evidence supports a connection between formaldehyde exposure and leukemia. Also, the World Health Organization has indicated that normal human exposures to formaldehyde do not present a risk of cancer.”

Critics also argue that there are detrimental economic and regulatory effects if a substance is listed on the RoC.

“When a substance is listed in the RoC, companies that rely on that substance for their production can often encounter significantly increased insurance rates, higher employee turnover, scrutiny from the trial bar, and strained relations with their communities,” Carrabba said.

“All of this comes in addition to the significant other consequences that, while not specifically regulatory, significantly increase the cost of doing business,” added Carrabba. “For small manufacturers in a bad economy increased costs could easily lead to closed doors.”

The 13th Report on Carcinogens is still in production.

NTP is an interagency program headquartered at the National Institute of Environmental Health Sciences, a branch of the National Institutes of Health.

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