Data regarding postmenopausal women for this cross-sectional study were obtained from the 2005–2008 National Health and Nutrition Examination Survey (NHANES), a nationwide survey conducted by the National Center for Health Statistics. Participants underwent health and nutritional assessments, including anthropometric measurements, laboratory tests, and questionnaires. The study was approved by the Research Ethics Committee of the National Public Health Institute. The study protocol did not require approval from the Institutional Review Board of Hangzhou Women’s Hospital. Postmenopausal women with aMED assessment and insomnia symptoms were included. Participants with extreme energy intake (<500 kcal or > 5,000 kcal) and missing key covariates were excluded. Specifically, 487 participants were excluded due to missing data on sedentary behavior, 73 for extreme energy intake, and two for missing insomnia data. Ultimately, 1,793 postmenopausal women were included in the final analysis. The selection process is shown in Figure 1.

In the NHANES questionnaire, sedentary behavior included sitting at work, at home, during transportation, and while socializing, such as desk work, commuting, reading, playing card games, watching TV, or using a computer, excluding sleep time (17). Sitting for more than 8 h/day was defined as sedentary behavior (18).

Adherence to the Mediterranean diet was evaluated using the aMED. Dietary intake data were collected through 24 h dietary recalls. The first recall was conducted during a face-to-face assessment at a mobile examination center (day one), while the second was conducted over the telephone (day 2) within 10 days of the initial interview. To calculate the aMED score, the participants’ intake of vegetables (excluding potatoes), legumes, fruits, nuts, whole grains, red/processed meat, fish, alcohol, and olive oil was assessed (19). The participants who scored above the median intake for fish, whole grains, legumes, nuts, fruits, vegetables, and olive oil received one point. For red/processed meat and alcohol, the individuals were awarded one point if their consumption was below the median or if they had moderate alcohol intake. Those who did not meet these criteria received zero points (20). Higher aMED scores indicated better adherence to the Mediterranean diet.

Insomnia symptoms were diagnosed using the NHANES sleep disorders questionnaires, which included three questions regarding the frequency of trouble falling asleep (SLQ080), prolonged nocturnal awakening (SLQ090), and undesired early morning awakening (SLQ100) in the previous month. These symptoms are included in the definition of insomnia in the Diagnostic and Statistical Manual of Mental Disorders, 5th edition (DSM-V) (21). Insomnia is diagnosed when an individual reports experiencing at least one of these symptoms five or more times within the past month (22, 23).

Potential covariates included age, ethnicity, education level, poverty-to-income ratio (PIR), occupation, body mass index (BMI), C-reactive protein, vitamin D, use of female hormones, anxiolytics, sedatives, and hypnotics, depression, history of CVD, cancer or malignancy, smoking status, drinking status, hypertension, diabetes, dyslipidemia, physical activity, energy intake, alcohol consumption, and caffeine intake. During the NHANES household interview, data on age, gender, ethnicity, education level, occupation, use of female hormones, anxiolytics, sedatives, and hypnotics, smoking status, drinking status, energy intake, alcohol consumption, and caffeine intake were collected using questionnaires. The PIR was the ratio of monthly family income to the poverty threshold specific to family size, as released by the Health and Human Services poverty guidelines. BMI was calculated as weight divided by height squared (kg/m²). Laboratory tests included C-reactive protein and vitamin D. Vitamin D ≥75 nmol/L was defined as adequate, while <75 nmol/L was considered insufficient. Depression was determined based on a 9-item Patient Health Questionnaire (PHQ-9) score of ≥10 (24). Cancer diagnoses were based on the following questions (25): (1) Have you ever been told by a doctor or other health professional that you had cancer or a malignancy of any kind? (2) What kind of cancer was it, and when was it diagnosed? Hypertension was defined as self-reported hypertension, a systolic bold pressure ≥140 mmHg, a diastolic blood pressure ≥90 mmHg, or the use of antihypertensive drugs (26). Diabetes was defined as self-reported diabetes, a fasting plasma glucose level of 126 mg/dL or more, or a hemoglobin A1c level of 6.5% or more (27). Dyslipidemia was defined as having high triglyceride levels or hypercholesterolemia (28).

Sampling weights (WTMEC2YR, SDMVPSU, and SDMVSTRA) were used in all analyses to generalize results to the U.S. civilian non-institutionalized resident population. The data were presented as count (%) for categorical variables and mean ± standard error (SE) for continuous variables. Comparisons between the two groups were conducted utilizing chi-square tests and t-tests. Potential covariates were selected using weighted univariate logistic regression models. The associations between sedentary behavior, adherence to the aMED, and insomnia symptoms were explored using weighted univariate and multivariate logistic regression models. The results were expressed as odds ratios (ORs) with 95% confidence intervals (CIs). All analyses were conducted using SAS 9.4 (Institute Inc., Cary, NC, United States), and p < 0.05 was considered statistically significant.

Data from 2,355 postmenopausal women, collected between 2005 and 2008, were analyzed. The mean age was 61.95 (0.42) years, with 960 (78.53%) women identified as non-Hispanic White. A total of 327 (18.24%) women reported sedentary time of ≥8 h. Insomnia symptoms were present in 643 (37.56%) women, and 736 (39.38%) exhibited high adherence to the aMED. Statistical differences were found between the two groups in occupation, BMI, physical activity, prolonged nocturnal awakening, and undesired early morning awakening. Table 1 presents the characteristics of the postmenopausal women.

After adjusting for age, ethnicity, occupation, anxiolytics, sedatives, hypnotics, depression, and smoking status, sedentary time of ≥8 h was associated with increased odds of insomnia symptoms (OR = 1.41, 95% CI: 1.01–1.96). In addition, sedentary time of ≥8 h was also related to a higher risk of prolonged nocturnal awakening (OR = 1.38, 95% CI: 1.06–1.79) and undesired early morning awakening (OR = 1.59, 95% CI: 1.09–2.30) in the adjusted model. No significant association was observed between adherence to aMED alone and insomnia symptoms (OR = 1.05, 95% CI: 0.77–1.44). Table 2 shows the relationships between sedentary behavior, adherence to the aMED, and insomnia symptoms in the postmenopausal women.

Figure 2 shows that adherence to the aMED influenced the association between sedentary behavior and insomnia symptoms. After adjusting for age, ethnicity, occupation, anxiolytics, sedatives, hypnotics, depression, and smoking status, among the postmenopausal women with lower adherence to the aMED, the odds of insomnia symptoms were higher in those with sedentary time of ≥8 h (OR = 1.63, 95% CI: 1.02–2.62). Similarly, among the postmenopausal women with lower adherence to the aMED, sedentary time of ≥8 h was also associated with prolonged nocturnal awakening (OR = 1.90, 95% CI: 1.27–2.83) and undesired early morning awakening (OR = 1.85, 95% CI: 1.09–3.16). Among the women with high adherence to the aMED, no association between sedentary behavior and insomnia symptoms was observed (OR = 1.14, 95% CI: 0.71–1.83). The findings suggest that adherence to the aMED may modulate the relationship between sedentary behavior and insomnia symptoms in postmenopausal women.