Women who work rotating night shifts for a number of years may have an increased risk of dying from heart disease and lung cancer, a new study suggests.

It is already known that sleep is essential for good health, therefore disruptions to the circadian rhythm - the body's internal clock - can have a negative effect.

US scientists decided to look into this further by assessing potential links between rotating night shifts and mortality, including heart disease and cancer-related mortality.

They defined rotating night shifts as working at least three nights per month, along with days or evenings in that month.

They followed the progress of almost 75,000 nurses over a 22-year period and found that those who worked rotating night shifts for at least five years had an increased risk of dying from cardiovascular disease.

Overall, those who worked these shifts for between six and 14 years had a 19% increased risk of dying from cardiovascular disease, while those who worked 15 years or more had a 23% increased risk.

Meanwhile, the scientists found no link between rotating shifts and cancer-related mortality, except when it came to lung cancer. Those who worked these shifts for 15 years or more had a 25% increased risk of dying from lung cancer.

"These results add to prior evidence of a potentially detrimental relation of rotating night shift work and health and longevity," they commented.

Details of these findings are published in the American Journal of Preventive Medicine.