Those who regularly work night shifts know it can throw off their body clocks. But a new study suggests the consequences can be far more severe.

In a draft report, the National Toxicology Program asserts that night shift work may lead to cancer. The NTP based its findings on a review of prior scientific studies on circadian rhythm disruption and artificial-light exposure.

There are nearly 15 million Americans who work full-time on evening, night, rotating or other irregular schedules, according to the Department of Health and Human Services. Many thousands of these people work in senior living settings, where around-the-clock service is required.

Experts say that appropriate nutrition is especially important for those who work at night.

The preliminary conclusion will be peer-reviewed and will be the focus of a public meeting in October. The NTP is run by the Department of Health and Human Services.