Timing of Dinner and Bedtime Tied to Increased Cancer Risk

Pam Harrison

July 25, 2018

Eating dinner before 9 pm and going to bed at least 2 hours after finishing the meal both significantly lower the risk for both breast and prostate cancer, a Spanish population-based study suggests.

These two cancers have already been shown to be linked to night shift work.

"The present study suggests that changes in timing of circadian controlled activities in sleep or diet that are less extreme than those observed in night shift work are associated with long term health effects, increasing the risk of the most prevalent cancers worldwide," the investigators state.

"Findings highlight the importance of assessing circadian rhythms in studies on diet and cancer," they add.

The authors, led by Manolis Kogevinas, MD, PhD, the Barcelona Institute for Global Health (ISGlobal), Spain, note that previous studies on nutrition and cancer have focused on types of foods (eg, fruits and vegetables) and quantity of food intake, rather than on the timing of eating.

"Subjects having both earlier supper (before 9 pm) and long interval between supper and sleep (>2 hr) had an approximately 25% decreased combined cancer risk...compared with those having supper after 10 pm and short supper-sleep interval," the investigators write.

If these findings are confirmed, "the impact could be especially important in cultures such as those of southern Europe, where people have supper late," Kogevinas added in a statement.

The study was published online July 17 in the International Journal of Cancer.

The findings come from the MCC-Spain study, a population-based, case-control study carried out in 12 regions in Spain between 2008 and 2013.

After excluding individuals who had ever worked the night shift, the analysis included 1205 patients with breast cancer and 621 patients with prostate cancer.

Another 1321 women and 872 men randomly selected from primary health centers in the same regions of Spain served as controls.

Information on participants' chronotype (ie, whether they were morning or evening persons) and the degree to which they followed cancer prevention recommendations of the World Cancer Research Fund/American Institute of Cancer Research (WCRF/AICR) was also assessed.

Approximately 27% of women who had been diagnosed with breast cancer were found to have a healthy lifestyle, as reflected by WCRF/AICR scores, compared with 31% of female control persons. A similar difference was seen between men who had been diagnosed with prostate cancer and male control persons.

"Cancer risk decreased with increasing time between supper (main evening meal) and sleeping," Kogevinas and colleagues report.

For example, participants who went to bed at least 2 hours after their evening meal had a 20% lower risk for breast and prostate cancer combined, an effect that was "slightly more pronounced" for prostate cancer than for breast cancer.

Eating prior to 9 pm was similarly associated with about a 20% lower risk for both cancers compared with eating after 10 pm, an effect that was again slightly more pronounced for prostate cancer than for breast cancer.

The researchers assessed the association of chronotype with both types of cancer and found that the amount of time between the evening meal and going to bed was most protective for morning types.

For morning types, the risk for both cancers was 34% lower when persons allowed at least 2 hours to elapse before going to bed, compared with only 14% for evening types, the authors note.

Not unexpectedly, "high adherence to cancer prevention policies was associated with a protective effect for breast cancer...compared with low adherence," the authors observe.

This effect was less pronounced for prostate cancer, they add.

Still, those who went to bed 2 hours after completion of the evening meal had a 35% lower risk for both cancers if they had closely followed cancer prevention recommendations, compared to only 10% for those who had the lowest level of adherence to recommendations.

ISGlobal coauthor Dora Romaguera, PhD, cautioned that further research in humans is necessary in order to elucidate how the timing of meals could affect cancer risk for breast and prostate cancer.

"However," she added in a statement, "everything seems to indicate that the timing of sleep affects our capacity to metabolize food," she said.

Eating Behaviors

Asked by Medscape Medical News to comment on the findings, Mark Guinter, PhD, MPH, American Cancer Society, Atlanta Georgia, noted that he has had a long-standing interest in studying eating behaviors, including the timing and frequency of meals and how they relate to a number of cancer risk factors and outcomes.

"I was involved in a prior study [not yet published] where we looked at breakfast consumption in relation to overweight and obesity status among women," Guinter elaborated.

"Our results showed that women who never consumed breakfast or who consumed breakfast every day were less likely to be overweight and obese compared to women who ate breakfast 3 to 4 days per week," he noted.

The same study also showed that women who never or always consumed breakfast were less likely to become overweight or obese after 5 years of follow-up, Guinter added.

As for findings from the MCC-Spain study, Guinter cautioned that it is important to analyze risk factors at an individual level and not as they might pertain to how a country behaves as a whole.

He noted that animal research suggests that the timing of food intake can influence the expression of genes that are related to circadian rhythms.

"Disruption of these circadian rhythms can be both harmful and protective, depending on how the genes are expressed," Guinter explained.

"But one way in which they are expressed is in an increase in systemic inflammation," he added.

"So the hypothesis that food intake influences circadian rhythms and that these in turn affect your daily physiological processes is absolutely plausible," he suggested.

Guinter indicated that it is too early to recommend eating before 9 pm and allowing 2 hours to elapse between the end of the evening meal and bedtime.

Still, "this is a hot area of interest," he noted.

"I think people will continue to build on these results, and then hopefully we'll be able to take them and develop more studies that result in recommendations than help people improve their lifestyle and prevent cancer," he said.

ISGlobal is supported by La Caixa Banking Foundation. The authors and Dr Guinter have disclosed no relevant financial relationships.

Int J Cancer. Published online July 17, 2018. Full text

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