A decreased number of hours spent eating each day and an increased number of hours spent fasting overnight may reduce a woman's risk for breast cancer by improving biomarkers of glycemic control, according to research presented at the AACR Annual Meeting 2015.  This study is being published simultaneously in Cancer Epidemiology, Biomarkers & Prevention, a journal of the American Association for Cancer Research.

"We found that women who fasted for longer periods of time overnight had significantly better control over blood glucose concentrations and these effects were independent of how much they ate,"  said Catherine Marinac, a doctoral candidate in public health at the University of California, San Diego. "This finding is relevant to cancer research because people who have poor glucose control are more likely to develop certain types of cancer, and it is hypothesized that high concentrations of circulating glucose may fuel cancer growth and progression.

"If these findings are reproduced, it would mean that increasing the duration of overnight fasting could be a novel strategy to reduce the risk for developing breast cancer," Marinac added. "This is a simple dietary change that we believe most women can understand and adopt, and it may have a big impact on public health."

According to Marinac, research in mice has suggested that decreasing the number of hours spent eating during the day and increasing the length of time of fasting overnight may improve metabolic parameters and reduce the risk of developing a number of chronic diseases including cancer. To explore this association further in humans, Marinac and colleagues looked at possible associations between the duration of nighttime fasting and glycemic control biomarkers that are linked to increased breast cancer risk.

The researchers found that for each three-hour increase in nighttime fasting, women had a 4 percent lower two-hour postprandial blood sugar measurement, which measures blood sugar two hours after starting a meal, and a nonsignificant 0.4 unit decrease in hemoglobin A1c (HbA1c), a measure of blood sugar control. Each three-hour increase in nighttime fasting was also associated with about 20 percent reduced odds of having elevated HbA1c and nonsignificantly reduced odds of an elevated two-hour postprandial blood sugar measurement.

"Our group is hoping to gain funding for a large-scale trial to confirm these findings," Marinac said.

The study included data from a sample of women with a median age of 47 years taken from the 2009-2010 United States National Health and Nutrition Examination Survey. Data on HbA1c over the previous two to three months were available for 2,212 women. Data on two-hour postprandial blood sugar were available for 1,066 women.

This study was funded by the National Cancer Institute. Marinac declares no conflicts of interest.