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New research published in Sleep Health sheds light on how daytime sleepiness and body weight are interconnected over time, revealing key sex differences. The study found that men with higher levels of daytime sleepiness had consistently higher body mass index (BMI), while women who experienced increasing daytime sleepiness over time showed faster weight gain. Among women, this effect was most pronounced in younger participants.
Obesity is a significant public health challenge, increasing the risk of numerous chronic health conditions and premature mortality. Sleep disturbances, including daytime sleepiness, are often associated with obesity. While much research has focused on how obesity contributes to sleepiness—through mechanisms like sleep apnea—fewer studies have explored the reverse relationship: whether sleepiness itself can lead to weight gain.
This new study sought to fill this gap by examining how both levels and changes in daytime sleepiness influence BMI trajectories over time. Importantly, the researchers aimed to uncover potential differences between men and women, as previous studies suggest that obesity and sleep-related factors often differ by sex. By using longitudinal data and objective measures of sleepiness, the researchers hoped to gain deeper insights into the potential feedback loop between sleep health and weight gain.
The research utilized data from the Wisconsin Sleep Cohort Study, which began in 1988 and included a randomly selected sample of Wisconsin state employees aged 30 to 60. Participants underwent repeated sleep studies at roughly four-year intervals, contributing to a robust dataset spanning over two decades. For this study, data from 827 participants were analyzed, representing a total of 2,614 sleep study observations.
Daytime sleepiness was objectively measured using the Multiple Sleep Latency Test (MSLT), which records the time it takes for a person to fall asleep during controlled nap trials. Shorter sleep latencies indicate greater sleepiness. BMI was calculated at each visit based on height and weight measurements taken by trained technicians. The researchers also accounted for factors such as age, physical activity, stimulant use, and depressive symptoms.
The study revealed connections between daytime sleepiness and BMI trajectories, with distinct patterns for men and women. For men, higher levels of daytime sleepiness were consistently associated with higher BMI levels across the study period. This relationship suggests that men who are chronically sleepier during the day tend to maintain higher BMI levels compared to their less sleepy counterparts.
Interestingly, this association was observed at a between-person level, meaning that men with more significant daytime sleepiness generally had higher average BMI levels than other men. However, changes in sleepiness over time among men were not strongly linked to within-person changes in BMI. In other words, men who were consistently sleepier did not experience significant weight changes over time relative to themselves, even though they tended to have higher BMI levels overall compared to other men in the study.
For women, the findings were more dynamic. While baseline levels of sleepiness were not significantly associated with BMI, changes in sleepiness over time had a pronounced effect on BMI trajectories. Women who experienced increases in daytime sleepiness tended to gain weight more rapidly than those whose sleepiness levels remained stable or decreased. This relationship was particularly pronounced in younger women, indicating that age may play a role in how sleepiness impacts weight gain.
The stronger association in younger women could be influenced by hormonal changes, metabolic factors, or differences in activity levels compared to older women. These findings highlight the importance of monitoring sleep health as a potential factor in weight management for women, especially during early adulthood.
The researchers proposed several pathways through which daytime sleepiness might contribute to weight gain. Sleepiness may reduce physical activity, as individuals with low energy levels are less likely to engage in exercise or maintain an active lifestyle. Sleepiness has also been linked to changes in dietary preferences, such as increased cravings for high-fat or high-calorie foods, which can contribute to weight gain. Additionally, metabolic factors, including insulin resistance or altered energy regulation, may be influenced by chronic sleep deprivation or excessive daytime sleepiness.
Interestingly, the study did not find evidence that sleep apnea—the most common medical explanation for daytime sleepiness—was the primary mediator of these relationships. Although sleep apnea is a known contributor to both sleepiness and obesity, the findings suggested that the association between daytime sleepiness and BMI exists independently of sleep apnea severity. This independence underscores the broader impact of sleepiness on weight regulation, beyond its role as a symptom of specific sleep disorders.
While the study provides valuable insights, it is not without limitations. First, although daytime sleepiness and BMI were measured objectively, other factors like physical activity and dietary habits were self-reported, which could introduce bias. Additionally, the study sample was predominantly white and middle-aged, limiting the generalizability of the findings to more diverse populations.
The study, “Objectively measured daytime sleepiness predicts weight change among adults: Findings from the Wisconsin Sleep Cohort Study,” was authored by Yin Liu, Jodi H. Barnet, Erika W. Hagen, Paul E. Peppard, Emmanuel Mignot, and Eric N. Reither.
