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

This study aimed to investigate the moderating effect of sleep quality on the relationship between dietary pattern and blood pressure. 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. After controlling for covariates, the interaction between MDS and PSQI was significantly associated with systolic blood pressure ( β = 1.112, t = 2.339, 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 associated with lower systolic blood pressure, but this association did not reach statistical significance ( β = -3.255, t = -1.454, P = 0.148, 95% CI : -7.673 to -1.162). At the mean level of PSQI, the association between MDS and systolic blood pressure was near zero and non-significant ( β = -0.046, t = -0.027, P = 0.0.978, 95% CI : -3.381 to 3.289). Among participants with higher PSQI scores, indicating poorer sleep quality, the association shifted to a positive direction and was also non-significant ( β = 3.164, t = 1.497, P = 0.136, 95% CI : -1.006 to 7.334). In this cross-sectional study of middle-aged and older adults, a healthier dietary pattern was associated with lower systolic blood pressure, and this association differed according to sleep quality levels: the inverse association was strongest among participants with better sleep quality and was attenuated as PSQI scores increased. The MDS × PSQI interaction remained significant after adjusting for multiple covariates and was consistent across continuous and dichotomized PSQI analyses. These findings suggest that sleep quality may be an important contextual factor when evaluating the blood pressure benefit of a healthy diet. Given the cross-sectional design and modest sample size, these results are hypothesis-generating and require confirmation in larger longitudinal and intervention studies.