Eat dinner earlier, dodge cancer?

While we often hear that breakfast is the most important meal of the day, new research suggests that we may need to take into consideration the importance of when we eat dinner.

In a new study published in The International Journal of Cancer, researchers noted that late night eating is associated with multiple different poor health outcomes, including cancer risk.

So, could cancer risk be, in part, related to when we eat dinner?

It’s important to understand that changes to normal sleep patterns have been associated with a number of common diseases, including cancer, cardiovascular disease, obesity, and type 2 diabetes. Research has also suggested a link between working at night and developing breast and prostate cancer.

“We know that breast and prostate cancer are very common and the most related to shift work and sleep-disruption," Dr. Manolis Kogevinas, the lead author of the study, told ABC News. "We know from experimental studies that timing of diet is important for health.”

The important relationship, the study shows, is between when people eat dinner and when they go to sleep and how that affects their risk of breast and prostate cancer.

These two types of cancer are more likely in people who eat just before bedtime, compared with those who leave at least two hours between dinner and going to sleep.

Researchers at the Barcelona Institute for Global Health compared over 1,800 people with prostate and breast cancer to over 2,100 people without cancer. These people were interviewed and provided questionnaires to understand multiple risk factors including physical activity level, sleep patterns, and dietary habits. Information on their diet included the number of meals, how long they lasted, and when they ate.

The researchers found that the risk of developing cancer decreased when there was a long period of time between eating dinner and sleeping. Men who report eating dinner at least two hours before going to sleep had a 26 percent decrease in prostate cancer compared to those eating immediately before bed. Women with the same dining pattern had a 16 percent decrease in breast cancer.

The time of day dinner was served was also associated with different cancer risks. People who had dinner before 9:00 p.m. had a 25 percent decrease in prostate cancer and a 15 percent decrease in breast cancer compared to people who had dinner after 10:00 p.m.

Depending on whether a person has a natural preference for morning or evening activities further influenced cancer risk. The decreased cancer risk with eating early dinner was even more pronounced in “morning people” compared to “evening people.”

Our bodies have evolved on a circadian rhythm or “clock” that signals when to eat and when to sleep, and modern living has been altering it.

Daylight and diet are the two most important factors that could impact someone’s circadian rhythm. People metabolize food differently depending on when they eat, and this affects health risks, according to Kogevinas, a research professor at Barcelona Institute for Global Health (ISGlobal) and former president of the International Society for Environmental Epidemiology.

“The underlying idea is that we have evolved as humans to do some things during the day and some things during the night and we have changed that,” Kogevinas explained.

Future work by the study authors will be aimed at further understanding this process.

Nutrition research often focuses on how much we eat, and how we eat. There is not a lot of information about the importance of when we eat. Furthermore, the study was done in Spain, where dinner is served later. It does not take into consideration other cultures that have an “after supper," or a smaller meal even later in the evening. These different patterns could lead to different cancer risks.

So should we start eating dinner earlier?

Cancer is complex and diet certainly is not the only thing that affects cancer risk. Researchers also looked at adherence to a healthy lifestyle as defined by the World Cancer Research Fund (WCRF) and American Institute for Cancer Research (AICR).

Those who ate dinner earlier and more closely adhered to a healthy lifestyle had a 35 percent decrease change of developing prostate and breast cancer. Those who ate dinner early but did not follow healthy lifestyle guidelines only had a 10 percent decrease.

Health lifestyle interventions shown by WCRF and AICR to reduce cancer risk include maintaining a healthy weight, engaging in physical activity, and eating a healthy diet with plant foods, whole grains, and low amounts of sugary drinks, alcohol, and salt.

But dinner timing still shows an effect.

“You don’t need research to tell you if you eat a lot or drink a lot and go straight to bed then you won’t sleep well that night,” Kogevinas explained. “What comes up clearly from this study and what we know from biology, is that eating at the wrong time may have a long-term effect.”

Michael MacIntyre, M.D., is a psychiatry resident working in the ABC News Medical Unit.