A new US study of nearly 6,000 women found that while regular exercise appeared to reduced their risk of cancer, this benefit was likely to be lost if they did not get enough sleep.

The researchers presented their findings at the American Association for Cancer Research’s (AACR) Seventh Annual International Conference on Frontiers in Cancer Prevention Research that is taking place in National Harbor, Maryland, this week. The press statement did not mention whether they intend to publish their findings in the AACR’s peer-reviewed journal Cancer Research, or any other.

Lead author and cancer prevention fellow at the National Cancer Institute in the US, Dr James McClain said:

“Greater participation in physical activity has consistently been associated with reduced risk of cancer incidence at several sites, including breast and colon cancers.”

“Short duration sleep appears to have opposing effects of physical activity on several key hormonal and metabolic parameters, which is why we looked at how it affected the exercise/cancer risk relationship,” he added.

Scientists don’t know exactly how exercise reduces cancer risk, but they suspect it is something to do with hormone levels and the immune system, and also because it affects body weight. In this study McClain and colleagues looked at the link between exercise and cancer, with particular attention to how not getting enough sleep might affect it.

While there are lots of studies looking at the links between sleep, exercise and health, not many are looking specifically at cancer, said the researchers in a press statement.

For the study the researchers used data taken from 5,968 cancer-free women aged 18 years and over who completed an initial survey in 1998 and were then monitored for nearly 10 years through State Cancer Registries in Washington County and Maryland.

From the questionnaire responses they compiled a measure of physical activity energy expenditure (PAEE) and assessed the link between this, sleep, and the incidence of overall, breast and colon cancer in the group of participants.

McClain said the findings suggest that:

“Sleep duration modifies the relationship between physical activity and all-site cancer risk among young and middle-aged women.”

604 of the women showed a first incidence of breast cancer and there was a significantly lower risk of overall and breast cancer among the women in the higher 50 per cent of PAEE or physical exercise level.

Among the women aged 65 and under in the upper 50 per cent of PAEE, those who had less than 7 hours sleep a day had the higher overall cancer risk, suggesting that much of the cancer-preventive benefit that might come from doing more physical activity could be undermined by lack of sufficient sleep.

However, these results need to be confirmed by more research, which is what McClain and colleagues plan to do next, as well as explore in more detail what the underlying mechanisms could be that link sleep and exercise in the prevention of cancer.

Click here for American Association for Cancer Research.

Sources: AACR.

Written by: Catharine Paddock, PhD