Adults who stay up late and are more active at night may face significantly worse cardiovascular health risks than their daytime counterparts, according to a new study. 

The prospective study, published online on January 28 in the Journal of the American Heart Association, included 322,777 UK Biobank participants aged 39 to 74. Results showed that those who were “definite evening” people had 79% worse scores on the American Heart Association’s “Life’s Essential 8 (LE8)” health metrics.

In contrast, “definite morning” people had a 5% lower prevalence of poor scores than the more typically timed group.

About 75% of the increased risk for cardiovascular disease (CVD) among evening people was tied to LE8 metrics for the modifiable behaviors and factors: healthy diet, regular physical activity, not smoking, quality sleep, weight, cholesterol, blood glucose, and blood pressure.

“Individuals with an evening chronotype may particularly benefit from interventions targeting CVD risk factors,” the authors wrote.

Circadian Clocks

Sleep is influenced by a person’s intrinsic circadian timing system. Mismatches between behaviors that drive sleep-wake cycles and one’s internal circadian clock can lead to adverse cardiometabolic outcomes. A person’s chronotype, the natural preference for sleep-wake timing, “may be a marker for underlying circadian misalignments,” the authors wrote.

This study evaluated associations between chronotype and cardiovascular health, according to LE8 metrics.

The UK Biobank participants (mean age, 57 years; 47% men; 96% White) self-identified as “definite evening” chronotype (8%) or “definite morning” chronotype (24%). Those who were unsure or lacked a sleep-wake preference were included in the intermediate chronotype (67%). At baseline, none had known CVD.

The “definite evening” chronotype was associated with lower LE8 scores, with the strongest associations seen for nicotine exposure (prevalence ratio, 1.54; 95% CI, 1.50-1.58) and inadequate sleep (prevalence ratio, 1.42; 95% CI, 1.36-1.48), followed by physical activity, blood glucose, weight, and diet. Associations between evening chronotype and blood pressure or cholesterol were negligible.

Over a median of 13.8 years of follow-up, 18,305 CVD events occurred, including 11,091 myocardial infarctions and 7214 strokes. Evening chronotype was associated with a modestly increased risk for CVD compared with intermediate chronotype. Adjusted for sociodemographic factors, shift work, and family history of CVD, the hazard ratio for total CVD was 1.16 (95% CI, 1.10-1.22) for the “definite evening” chronotype and 1.03 (95% CI, 0.998-1.07) for the “definite morning” chronotype.

Confounders for Sleep Research

The study “reaffirms that sleep impacts cardiovascular health,” said Joshua Liberman, MD, president and owner of Wisconsin Cardiology Associates, SC, in Mequon, Wisconsin. Liberman was not involved in the research.

However, “there are a lot of confounders — which is a problem for sleep research in general,” Liberman said. “Alcohol use, sleep apnea, and socioeconomic situations also impact heart health, as well as sleep.”

He also noted that participants who lacked complete LE8 scores were excluded from the analysis, presenting possible selection bias for a healthier cohort.

The observational findings suggest clinicians should consider monitoring patients with evening chronotype closely, lead author Sina Kianersi, PhD, DVM, told Medscape Medical News. Kianersi is a research fellow in the Division of Sleep and Circadian Disorders at Brigham and Women’s Hospital and Harvard Medical School, both in Boston.

Future research on chronotype and CVD could develop targeted interventions or personalized messaging to improve patient outcomes, “to really see what can work and how much it can decrease risk for night owls,” he said.

The research was funded by the American Heart Association, the National Heart, Lung, and Blood Institute of the National Institutes of Health, and the National Institute on Aging. One author reported two financial disclosures that are fully listed in the original article. The other researchers reported no relevant financial relationships.

Kat Long is a science journalist in the Washington, DC area.