Many companies require that their employees work on a rotating night shift. This means that they are on a day shift for a while and then work at night some, too. Now researchers are saying that this technique may actually increase the risk of cancer.

In a new study, a rotating night shift was defined as being on the night shift at least three times per month, and also working on the day shift. One career field where this is common is nursing. Nurses often work 12-hour shifts, and rotating shifts is common practice.

A study was conducted by Dr. Eva Schernhammer at the Harvard Medical School. The study looked at the records of 75,000 nurses all across the United States. It reviewed their information over a 22-year period.

Because of the nature of the study, it cannot actually prove that working the night shift causes cancer, but it can prove that there is a strong relation. What the study revealed was that people who had worked on a rotating shift for more than five years had an 11 percent greater risk of death from all causes than those who were never on a rotating shift.

The risk is increased the longer that someone continues to work on this rotating shift basis. The risk of suffering from heart disease is 19 percent higher for those who worked on rotating shifts for six to 14 years. The risk is raised to 23 percent if they continue to work on a rotating shift for 15 years or longer. The results of the study were reported in the American Journal of Preventive Medicine.

Studies have previously shown that there is a connection between night shift work and some forms of cancer. This includes lung cancer, breast cancer, and ovarian cancer. It was also noted that the risk really only appears to be true of women over 50.

The study performed by Schernhammer did not find any connection between working on a rotating shift and cancer mortality. It was a connection in the development of the cancers, particularly lung cancer.

Another earlier study found that working on the night shift increases the likelihood for breast cancer. For women on the night shift, the risk is up to 40 percent. It is four times higher in women who are considered to be a morning person.

One theory in relation to the breast cancer threat is that working under artificial light at night will decrease the amount of melatonin the body produces. Melatonin is known to help fight cancer.