How do circadian rhythms affect cardiometabolic disease risk, and what does the 2025 American Heart Association statement add?

Why does a disrupted body clock raise cardiometabolic risk?

The circadian system regulates 24-hour rhythms across many physiological processes, including blood pressure, vascular tone, endothelial function, insulin sensitivity, and inflammation—all directly relevant to heart and metabolic health [1][4]. When these rhythms are disturbed, these processes can fall out of sync, which may contribute to conditions like obesity, type 2 diabetes, hypertension, and cardiovascular disease [1][3]. For example, circadian disruption has been linked to metabolic conditions such as diabetes, obesity, and fatty liver disease, and it may also promote a proinflammatory environment through effects on the gut microbiome [3].

The disruption can happen in several ways. Sleep irregularity—high day-to-day variability in sleep timing or duration—is thought to reflect both disturbed sleep and circadian disruption, and it has emerged as one of the most significant sleep measures associated with cardiovascular health and mortality in studies that evaluated multiple sleep dimensions [4]. Shift work and other forms of circadian misalignment can disturb the immune system's own rhythms, potentially increasing infection risk, and circadian disturbances have been linked to a range of other illnesses [3]. These findings are largely from observational and mechanistic studies, so they suggest associations and plausible pathways rather than proven cause-and-effect in every case.

What does the 2025 AHA statement add?

The 2025 American Heart Association scientific statement provides an overview of the circadian system and identifies key behavioral factors that can synchronize or desynchronize circadian rhythms: light exposure, food intake, physical exercise, and sleep timing [1]. It summarizes the literature linking circadian health to cardiometabolic indicators such as excessive weight, type 2 diabetes, hypertension, and cardiovascular disease [1]. This is a formal consolidation of evidence from a major health organization, which gives the topic more clinical visibility and emphasizes that circadian health is modifiable.

The statement also proposes strategies to improve circadian health by targeting these synchronizers with appropriate timing. These include morning bright light exposure and avoidance of light at night, as well as appropriately timed sleep, meals, and exercise [1]. It calls on clinicians, researchers, policymakers, and the public to recognize the role of circadian rhythms in cardiometabolic health and to focus on identifying modifiable behaviors that can improve them [1]. The statement does not present new primary data; it is a review and recommendation, so its advice is based on the existing evidence base rather than a single new trial.

Which daily behaviors can help keep rhythms aligned?

The most concrete takeaway from the AHA statement is that timing matters. Morning bright light helps set the master clock, while light at night can push rhythms later and disrupt them [1]. Similarly, the timing of meals and exercise can either reinforce or conflict with the body's internal schedules [1]. Sleep timing—going to bed and waking at consistent times—is another key synchronizer, and sleep irregularity has been specifically linked to higher risk of weight gain, obesity, metabolic dysregulation, hypertension, diabetes, and cardiovascular disease in large prospective studies [4].

For people with circadian rhythm sleep-wake disorders, treatment often combines timed light exposure, melatonin or melatonin agonists, and behavioral interventions [3]. The AHA statement's recommendations are broader and preventive: it suggests that aligning light, food, exercise, and sleep with the body's natural rhythms could help maintain cardiometabolic health [1]. However, the statement does not quantify how much risk reduction these timing strategies produce, and the evidence for interventions that specifically promote sleep regularity is still limited—one review concluded there is a need to study such interventions as a strategy to reduce cardiometabolic disease risk [4].

How strong is the evidence, and what is still unclear?

Much of the evidence linking circadian disruption to cardiometabolic disease comes from observational studies and mechanistic research, which can show associations and plausible biological pathways but cannot always prove causation [1][4]. Some studies, such as those using Mendelian randomization, provide stronger support for causal links between certain sleep traits and disease, but these are not available for every circadian measure [4]. The AHA statement itself is a review of existing literature, not a new empirical study, so its conclusions reflect the strength of the underlying evidence [1].

There are also open questions about which interventions work best and for whom. For instance, cognitive behavioral therapy for insomnia appears less effective for the insomnia-with-short-sleep subtype, and it has not yet been shown to reduce cardiovascular disease in patients with insomnia [4]. The statement calls for identifying modifiable behaviors that can improve circadian health, but it does not specify how much benefit comes from each behavior or how to tailor recommendations to different populations [1]. Future research will need to test whether timing-based interventions actually lower cardiometabolic risk in randomized trials.

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