In a recent study published in the journal Nutrients, researchers investigated the additive effects of breakfast-eating habits and sleep timing on cardiovascular health. Their large-scale study included 16,121 participants assigned to four cohorts based on their sleep and eating patterns. Their findings highlight that going to bed late combined with skipping breakfast contributed to metabolic syndrome (MetS) and cardiovascular disease (CVD) risk in men. Surprisingly, both sex and age were found to alter the effects of breakfast and sleep on CVD risk.
Study: The Relationship between Breakfast and Sleep and Cardiovascular Risk Factors. Image Credit: Created with the assistance of DALL·E 3
Modifiable behaviors contributing to CVD
Cardiovascular disease (CVD) is a cohort of conditions responsible for more human deaths than any other. Alarmingly, CVD prevalence is on the rise, with 12.1 million deaths in 1990 jumping to 20.5 million in 2021. A number of modifiable behaviors have been associated with CVD risk, especially diet, exercise, and sleep patterns.
Breakfast is considered the most important daily meal because it breaks the overnight fast, the most prolonged standard fasting period for most humans. An extensive body of research has assessed the health impacts of skipping breakfast and revealed that poor breakfast habits are directly proportional to CVD risk factors, including obesity, hypertension (HTN), diabetes mellitus (DM), and metabolic syndrome (MetS).
Scientists have also investigated the role of sleep patterns in CVD and found that low sleep duration is associated with increased obesity and MetS risk independent of dietary behavior. While most sleep research has focused on sleep duration, limited sleep timing-centric studies have revealed that inconsistent or late sleep timings can disrupt the natural circadian rhythm, adversely impacting cardiovascular health.
Hitherto, modifiable behaviors have been studied in isolation, with little to no investigations into their combined effects. Given that sleep timings and breakfast patterns are co-dependent – sleeping late increases the probability of late-night eating and skipping breakfast – evaluating the combined effects of sleep timings and breakfast habits might improve our understanding of critical interventions required to reduce CVD risk.
About the study
In the present study, researchers hypothesized that different combinations of sleep and breakfast habits, specifically early sleep + regular breakfast, early sleep + infrequent breakfast, late sleep + regular breakfast, and late sleep + infrequent breakfast, would contribute differently to CVD risk. They aimed to assess this risk by measuring CVD-associated risk factors, including DM, dyslipidemia (DL), HTN, and MetS, in adults and investigate if these risks varied by sex and age.
Their study cohort was derived from the Korea National Health and Nutrition Examination Survey (KNHANES), a long-term investigation into Koreans' nutritional status and general health conducted by the Korea Disease Control and Prevention Agency (KDCA). Their dataset comprised 25,341 individuals above the age of 19 years whose sleep patterns had been monitored for a minimum of four years. Individuals who failed to provide completed sleep or dietary records and those with renal dysfunction or a history of cancer were excluded from the study, resulting in a final dataset of 6,744 men and 9,277 women.
Participants were required to complete sleep questionnaires reporting their general sleep timings and durations on weekdays and weekends. Researchers used this data to analyze numerous sleep metrics, including mid-sleep on free days (MSF), MSF corrected for sleep debt (MSFsc), average weekly bedtime, and average weekly sleep duration. The corrected average bedtime across participants was revealed to be 23:17, so "early sleep" was defined as sleeping before 23:17, and late sleep was defined as sleeping after 23:17.
Participants' daily breakfast habits were recorded and used to assign participants into two cohorts – 'infrequent breakfast eaters' (0-2 breakfasts per week) and 'regular breakfast eaters' (5-7 breakfasts per week). When combined with sleep data, this resulted in four cohorts corresponding to the researchers' original hypothesis. Additional participant data collected included age, daily nutritional intake, monthly household income, education status, smoking and alcohol consumption, menopause status (for women), and comorbidities (clinically diagnosed HTN, DM, or DL).
Deriving from the 2005 American Heart Association/National Heart, Lung, and Blood Institute criteria, MetS was evaluated based on waist circumference, serum triglyceride level, or serum high-density lipoprotein (HDL) cholesterol level. Finally, statistical analyses were stratified by sex and age (<50 or ≥50 years) and consisted of linear regression analyses, Kruskal-Wallis H tests, Mann-Whitney U tests, and chi-squared (χ2) tests.
Baseline differences between male and female cohorts were surprisingly different. Men had a greater probability of being employed, higher education status, higher smoking and drinking, and worse baseline CVD risk factors (BMI, obesity, HTN, DM, and MetS) than their female counterparts. Men depicted lower mean sleep durations (7.18 hours) compared to women (7.22 hours). As expected, men were observed to have higher protein and calorific intake than women.
"After controlling for potential confounding variables, in men, group 4 (late sleep + infrequent breakfast eaters) had a lower prevalence of obesity than group 1 (early sleep + regular breakfast eaters) (OR 0.78, 95% confidence interval (CI) 0.62–0.97), and groups 2, 3, and 4 had a higher prevalence of MetS than group 1 (OR 1.43, 1.62, and 1.47, respectively)."
Differences between study cohorts were less distinct in women – group 4 women depicted higher DL prevalence than group 1. Group 2 women (late sleep + regular breakfast eaters) had a higher probability of MetS than group 1.
Age was seen to play a crucial role in participants' responses to sleep and breakfast behaviors. Under the age of 50, men in group 3 (early sleep + infrequent breakfast eaters) and group 4 depicted a higher likelihood of MetS than group 1, but this trend changed to groups 2 and 4 in men over 50. In women under 50 years, group 2 depicted lower obesity prevalence than group 1, but in women over 50, group 4 presented obesity and MetS risks higher than group 1.
In the present study, researchers evaluated the effects of sleep timings and breakfast consumption on CVD risk factors. Their findings suggest that the combined impacts of late sleep and skipping breakfast were associated with increased MetS risk, especially in men. Contrasting independent sleep and dietary studies, no associations were found between these combined behaviors and obesity, HTN, DM, and DL.
"…this study contributes to the understanding of the joint association between breakfast eating behavior and sleep timing on CVD risk factors. Moreover, the relationship between breakfast and sleep timing on CVD risk factors differed by sex and age group. Further research is warranted to explore the associations between breakfast and sleep timing on CVD risk factors across different sex and age groups."