Why breast cancer survivors should avoid late-night snacks

A patient undergoes a mammogram. The study will be of concern to breast cancer survivors. Photo / iStock

A study has linked a shorter gap between dinner and breakfast with a higher risk of a breast cancer recurrence in women.

The study, published in JAMA Oncology, examined data from more than 2400 women with early-stage cancer who were between ages 27 and 70 at the time of diagnosis.

It found a night-time fasting period of less that 13 hours was linked to a 36 per cent higher risk for a cancer recurrence, compared with fasting durations of 13 hours or more.

The study didn't find a link between the shorter fasting period and an increased risk of death from breast cancer or other causes.

Given those results, "prolonging the length of the nightly fasting interval may be a simple, non-pharmacologic strategy for reducing the risk of breast cancer recurrence," said the study authors, who were led by Ruth Patterson of the University of California's San Diego campus.

The researchers believed the study was the first involving humans that examined the link between nightly fasting and cancer outcomes.

"One reason we feel positive about this as a potential dietary behaviour is how simple it is," Patterson said.

"It's easier than saying reduce your calorie intake by 500 a day, which requires changes in how you shop, where you eat out, and can be very burdensome."

Gretchen Kimmick, an oncologist at the Duke Cancer Institute who wasn't involved in the study, said the findings were "hard to ignore". She said the study confirmed common sense: that sleeping longer and fasting longer is good for your health.

Patterson said there may be several reasons for the results: Eating late at night, for example, can result in worse sleep quality and might affect the way the body regulates sugar.

Each two-hour increase in nightly fasting was linked to lower levels of haemoglobin A1c - haemoglobin with glucose attached, a measure of the amount of sugar in the blood.

"Given the associations of nightly fasting with glycaemic control and sleep, we hypothesise that interventions to prolong the nightly fasting interval could potentially reduce the risk of type 2 diabetes, cardiovascular disease and other cancers," Patterson said.

She and her co-authors pointed out the study was based on self-reported dietary data, which is a limitation because it isn't always accurate.

Women in the study were an average of about 52 years old and fasted an average of 12.5 hours per night. A shorter night-time fasting period - less than 13 hours per night - was associated with college education, a lower BMI and less sleep.