Higher body roundness linked to sleep disorders, with depression playing a mediating role

New research published in BMC Psychiatry suggests that people with more abdominal body fat are more likely to experience sleep disorders, and this relationship is partly explained by symptoms of depression. The study found that a higher Body Roundness Index—a measure of body shape that reflects fat distribution, especially around the abdomen—was strongly associated with both depression and sleep problems.

Sleep disorders are a widespread public health issue affecting millions of adults. These conditions, which include insomnia, sleep apnea, and other disturbances, not only impair quality of life but are also tied to several physical and mental health problems.

Obesity, in particular, has long been identified as a risk factor for sleep disorders, but most studies have relied on Body Mass Index as the main measure of body fat. While BMI can be a useful screening tool, it does not provide information about fat distribution, which may be a more relevant factor in predicting health outcomes, especially those related to sleep.

The research team focused on the Body Roundness Index, or BRI, because it offers a more precise way to assess fat distribution, especially visceral fat—the type that surrounds internal organs. Visceral fat has been linked to metabolic disturbances, inflammation, and a host of negative health effects. At the same time, depression has been independently associated with both obesity and sleep disorders, leading the researchers to hypothesize that depression may act as a bridge that helps explain why excess fat around the midsection contributes to sleep problems.

To test this idea, the researchers analyzed data from the National Health and Nutrition Examination Survey, a large and ongoing study of health in the United States. They focused on adults aged 20 and older, ultimately including over 32,000 individuals in their analysis after excluding participants with missing data. The dataset included a range of information, such as height, waist circumference, mental health assessments, and self-reported diagnoses of sleep disorders made by health professionals.

Sleep disorder status was determined by asking participants whether a doctor had ever told them they had such a condition. Depression was measured using the Patient Health Questionnaire-9, a widely used clinical tool that asks about symptoms experienced in the previous two weeks. A score of 10 or higher on the questionnaire was used as the cutoff for identifying depression. The researchers also gathered data on a variety of other factors that might influence the results, such as age, sex, race, income, education, smoking status, alcohol use, and chronic health conditions like hypertension or diabetes.

The researchers conducted several statistical analyses to examine how BRI was related to sleep disorders and whether depression explained part of that link. They found that a higher BRI was significantly associated with a greater likelihood of having a sleep disorder. Even after adjusting for other variables, each one-unit increase in BRI was linked to a 13% higher risk of sleep problems. When the researchers divided participants into groups based on their BRI levels, those in the highest group were 50% more likely to report a sleep disorder than those in the lowest group.

Depression also played a notable role. The study found that people with higher BRI scores were more likely to be depressed, and depression was strongly related to the presence of sleep disorders. Mediation analysis showed that depression accounted for about 14% of the total relationship between BRI and sleep disorders. This suggests that while excess abdominal fat directly contributes to sleep problems, part of its impact may work through the psychological effects of depression.

The researchers also found evidence that the relationship between BRI and sleep disorders was not perfectly linear. A J-shaped pattern emerged, with a threshold around a BRI of 3.5. Below that point, higher BRI was actually associated with a slightly lower risk of sleep disorder, but above that point, the risk increased sharply. This finding supports the idea that there may be a critical level of visceral fat beyond which the risk of sleep problems rises significantly.

To further understand the predictive power of BRI, the team compared it to other body measurements like BMI, weight, and waist-to-height ratio. BRI outperformed all other metrics, suggesting it may be especially useful for identifying people at risk of sleep disorders. Subgroup analyses showed that the link between BRI, depression, and sleep disorders held across various groups, including different age ranges, sexes, and racial or socioeconomic backgrounds.

The researchers proposed some possible biological explanations for these links. One major factor is inflammation. Visceral fat is known to produce inflammatory molecules such as interleukin-6 and tumor necrosis factor-alpha, which can cross into the brain and interfere with sleep regulation. Hormonal imbalances, like reduced levels of the anti-inflammatory hormone adiponectin and resistance to leptin, a hormone that controls hunger and metabolism, may also contribute to disrupted sleep cycles.

Gut health may be another piece of the puzzle. People with more abdominal fat often experience changes in their gut microbiota, which in turn can affect brain function and sleep. For example, certain bacterial imbalances can increase the production of inflammatory compounds or disrupt neurotransmitters like serotonin and melatonin, both of which play a role in sleep regulation.

The psychological impact of obesity may also feed into the cycle. People with higher levels of visceral fat often experience reduced self-esteem and social stigma, which can contribute to depression. Depression, in turn, is known to disturb sleep by altering circadian rhythms, mood regulation, and the body’s stress-response system. Additionally, certain antidepressant medications are known to cause weight gain, which could further worsen both mood and sleep issues.

Despite its strengths—including a large and nationally representative sample—the study has limitations. Since the research design was cross-sectional, it cannot prove that higher BRI causes sleep disorders, only that the two are associated. Longitudinal studies are needed to better understand the direction of these effects over time. The study also relied on self-reported data for sleep disorders, which could introduce recall bias or underreporting. Future research using clinical sleep assessments or polysomnography would help validate the findings.

Another limitation is that depression was only found to explain part of the relationship between BRI and sleep disorders. Other psychological or physiological factors—such as anxiety, chronic stress, or hormonal disturbances—may also play a role and should be investigated in future studies. In addition, while the findings are relevant to adults in the United States, they may not generalize to populations with different lifestyles, diets, or healthcare systems.

The study, “Association between body roundness index and sleep disorder: the mediating role of depression,” was authored by Hongyang Gong and Yunkai Zhao.