New research from scientists at Brigham and Women's Hospital has found a strong association between irregular sleep patterns and an increased risk of metabolic disorders such as hypertension, obesity and diabetes. The study suggests there is a possible causal connection between inconsistent sleep schedules and metabolic dysfunction.

"Many previous studies have shown the link between insufficient sleep and higher risk of obesity, diabetes, and other metabolic disorders," explains study author Tianyi Huang. "But we didn't know much about the impact of irregular sleep, high day-to-day variability in sleep duration and timing."

The study followed over 2,000 subjects for an average of six years. It was discovered that those subjects with the greatest variation in bedtimes, and overall sleep duration, displayed the highest prevalence of metabolic disorders.

"Our research shows that, even after considering the amount of sleep a person gets and other lifestyle factors, every one-hour night-to-night difference in the time to bed or the duration of a night's sleep multiplies the adverse metabolic effect," says Huang.

The study is not without significant limitations. Alongside self-reported sleep diaries and questionaries, data that can often be subjectively biased, the participants were only objectively tracked for a seven-day stretch using actigraph wrist watches at the beginning of the study. So, it is unclear how consistent these irregular sleep patterns were across the entire six-year study.

It also isn't clear whether the data implies if irregular sleep patterns are worse than regular shorter sleep durations or consistent night-owl and shift worker sleeping habits, as previous research has made clear that shorter sleep times, or simply staying up late into the night, can have negative long-term health effects.

Huang, and study co-author Susan Redline, do suggest that their data indicates the more variability in a person's bedtimes and sleep durations, the higher the risk of a number of problems, from obesity to high blood pressure. The researchers also suggest that in many subjects, the variations in sleep patterns preceded the onset of a metabolic problem. This potentially indicates a causal link between the sleep irregularities and the subsequent health problems.

"Our results suggest that maintaining a regular sleep schedule has beneficial metabolic effects," study Redline. "This message may enrich current prevention strategies for metabolic disease that primarily focus on promoting sufficient sleep and other healthy lifestyles."

The new research was published in the journal Diabetes Care.