Sleep quality moderates the association between diet and blood pressure in middle-aged and older adults: a cross-sectional study

Objective This study aimed to investigate the moderating effect of sleep quality on the relationship between dietary pattern and blood pressure. Methods Using cross-sectional survey data from 201 middle-aged and older adults aged 45 years and above in a community in Shijiazhuang, Hebei Province in 2023, the Mediterranean Diet Score (MDS) and the Pittsburgh Sleep Quality Index (PSQI) were used to assess diet and sleep. A moderation model was employed to examine the moderating effect of different levels of sleep quality on the association between diet and blood pressure. Results After controlling for covariates, the interaction between MDS and PSQI was significantly associated with systolic blood pressure ( β = 1.029, t = 2.137, P < 0.05), indicating that sleep quality moderated the association between dietary pattern and blood pressure. Simple slope analysis showed that among participants with lower PSQI scores, indicating better sleep quality, higher MDS was significantly associated with lower systolic blood pressure ( β = -5.537, t = -2.530, P = 0.012, 95% CI : -9.852 to -1.221). At the mean level of PSQI, the association between MDS and systolic blood pressure was no longer significant ( β = -2.027, t = -1.266, P = 0.210, 95% CI : -5.184 to 1.131). Among participants with higher PSQI scores, indicating poorer sleep quality, the association became non-significant and positive in direction ( β = 1.483, t = 0.725, P = 0.470, 95% CI : -2.554 to 5.519). Exploratory subgroup analyses suggested that this moderating effect was evident mainly among overweight/obese participants (BMI ≥ 24.9 kg/m²) ( β = 0.734, 95% CI : 0.214 to 1.255, P = 0.006). Conclusion In this cross-sectional study, better sleep quality appeared to strengthen the inverse association between a healthier dietary pattern and systolic blood pressure among middle-aged and older adults. This association was attenuated as PSQI scores increased, suggesting that poorer sleep quality may weaken the potential blood pressure-related benefit of a healthy diet. These findings are hypothesis-generating and support the need for longitudinal and intervention studies to clarify whether improving sleep quality can enhance the cardiovascular benefits of dietary modification, particularly among overweight or obese individuals.