In patients with breast cancer, a short overnight fast of less than 13 hours was associated with a statistically significant, 36 percent higher risk of breast cancer recurrence and a non-significant, 21 percent higher probability of death from the disease compared to patients who fasted 13 or more hours per night, report University of California, San Diego School of Medicine researchers.

The study, publishing online in the Journal of the American Medical Association Oncology on March 31, also found a non-significant, 22 percent higher risk of mortality from any cause among patients with breast cancer who fasted for shorter periods compared to those who fasted for 13 hours or more overnight.

Researchers also reported that fasting fewer hours per night was associated with significantly less sleep and higher levels of glycated hemoglobin (HbA1c), which is a measure of average blood sugar levels over a period of months. These findings are relevant to cancer prevention and control efforts because elevated HbA1c and poor sleeping habits have been linked to an increased risk of breast cancer. These findings corroborate a paper published in April 2015, in which researchers demonstrated that shorter overnight fasts were associated with worse blood sugar control.

“Prolonging the overnight fasting interval may be a simple, non-pharmacological strategy for reducing a person’s risk of breast cancer recurrence and even other cancers,” said Catherine Marinac, lead author and doctoral candidate at UC San Diego Moores Cancer Center. “Previous research has focused on what to eat for cancer prevention, but when we eat may also matter because it appears to affect metabolic health.”

The study included 2,413 non-diabetic breast cancer survivors between the age of 27 and 70 who participated in a multi-institutional research study conducted between 1995 and 2007, with follow up for breast cancer recurrence and mortality. Participants were 86 percent non-Hispanic white and 55 percent were college educated.

“If future trials confirm that habitual prolonged nightly fasting improves metabolic health, this would be an important discovery in prevention that could reduce the risk of cancers, type 2 diabetes, and cardiovascular disease,” said Ruth Patterson, PhD, senior author and leader of the cancer prevention program at Moores Cancer Center.

Randomized trials to test whether prolonging overnight fasting reduces the risk of chronic diseases are needed, said the authors.

Additional study co-authors include Caitlin I. Breen, Sheri J. Hartman, Loki Natarajan, John P. Pierce, Shirley W. Flatt, and Dorothy D. Sears, UCSD; Sandahl H. Nelson, UCSD and San Diego State University.

This research was funded, in part, by the National Cancer Institute of the National Institutes of Health (F31CA183125, K07CA181323, U54CA155435, R01CA166293).