Circadian Misalignment and Glucose Management

A new study showed glucose tolerance is affected by the body’s internal clock, a findings that directly impacts daily blood glucose management.

“It’s not just what you eat, but also when you eat that greatly influences blood glucose regulation and that has important health consequences,” said study lead author Dr. Christopher Morris, a postdoctoral research fellow at Harvard Medical School.

The eight-day trial involved 14 healthy participants who first ate breakfast at 8 a.m., dinner at 8 p.m., and slept through the night. During the study’s second phase, the researchers flipped the script: Participants ate the day’s first meal at 8 p.m., the last meal at 8 a.m., and slept during the day.

Measurements of blood glucose and insulin levels taken every 10 minutes immediately after meals and hourly throughout the rest of the day revealed glucose levels were 17% higher in the evening than in the morning, regardless of when participants ate or slept. The findings confirmed that the body’s internal clock significantly impacts glucose tolerance, said the researchers. The study also noted that glucose levels were 6% higher when participants slept during the day and had breakfast at 8 p.m., a misalignment of the circadian rhythm that mimicked the schedule of night-shift workers.

“We also found that simulated night work lowered glucose tolerance throughout multiple days,” said study lead author Dr. Morris. “These two effects appear to be mediated, at least in part, by two different insulin-related mechanisms.”

It’s well known that glucose levels increase throughout the day, said the researchers, who suggested the impact of circadian misalignment on glucose tolerance could be partly explained by a 27% lower response to insulin in the evening caused by reduced beta-cell function and decreased insulin sensitivity. The researchers suggested circadian misalignment sent conflicting signals in the regulation of metabolism to the liver and pancreas, creating a struggle between the body’s internal clock and external behaviors that reduced beta-cell function and altered glucose management.

The body’s ability to manage blood sugar levels is best in the morning and worse at night, noted the researchers, who said a greater understanding of why those peak and trough levels occur is important to help prevent type 2 diabetes in high-risk individuals who work overnight or who are most active after the sun goes down.

The study was published online in the Proceedings of the National Academy of Sciences.

—Dan Cook

Reference:

1. Morris CJ, Yang JN, Garcia JI, et al. Endogenous circadian system and circadian misalignment impact glucose tolerance via separate mechanisms in humans. Proc Natl Acad Sci USA. 2015;112(17):E2225-E2234.