Estimated Habitual Dairy Polar Lipid Exposure and Post-Intervention Plasma Lipid Outcomes in Perimenopausal Women in Latvia: A Secondary Exposure-Based Analysis of a 28-Day Fermented Buttermilk Randomised Trial.

Background/Objectives: Hormonal changes during the perimenopausal period are linked to alterations in lipid metabolism and increased cardiovascular disease risk. Dairy polar lipids (PLs), including phosphatidylcholine (PC), phosphatidylethanolamine (PE), and sphingomyelin (SM), have attracted growing interest for their potential effects on intestinal cholesterol absorption, lipoprotein metabolism, and circulating lipid concentrations. However, evidence on habitual dietary exposure to naturally occurring dairy PLs remains limited. The aim of the present study was to estimate habitual dietary exposure to dairy PLs by integrating season-specific dairy product composition with individual dietary intake data, and to examine whether this estimated exposure was associated with post-intervention plasma lipid outcomes in perimenopausal women in Latvia. Methods: The analysis included 61 perimenopausal women, comprising an intervention group (n = 31) and a control group (n = 30), who were further stratified into winter and spring cohorts. The intervention group consumed 250 mL day^-1 of fermented buttermilk for 28 days. Dietary intake was assessed using a food frequency questionnaire (FFQ). Season-specific concentrations of total PL, PC, PE, and SM were quantified in locally produced dairy products using LC-ESI-MRM-TQ-MS/MS and integrated with individual dietary intake data to estimate dairy PL exposure. Multivariable linear regression models were adjusted for baseline lipid concentrations, intervention group, season, and total dairy PL intake. Results: Estimated total dairy PL intake was positively associated with post-intervention HDL-C concentrations in the adjusted models (β = 0.059; 95% CI: 0.020-0.099), whereas no statistically significant associations were observed for total cholesterol (TC), low-density lipoprotein cholesterol (LDL-C), or triglycerides (TGs). After adjustment for baseline lipid concentrations, season, and estimated total dairy PL intake, intervention-group allocation was associated with higher post-intervention TC (β = 0.485; 95% CI: 0.023-0.948) and LDL-C (β = 0.330; 95% CI: 0.024-0.636) than in the control group. The spring-versus-winter season indicator was not independently associated with lipid outcomes. Conclusions: Estimated habitual dairy PL exposure was positively associated with post-intervention HDL-C concentrations but not with TC, LDL-C, or TGs. These findings do not support a clear lipid-lowering effect of the 28-day fermented buttermilk intervention in this secondary, exposure-based analysis. The results should be interpreted with caution, as dairy PL exposure was estimated from FFQ-derived intake data and season-specific product composition rather than measured directly. This trial was retrospectively registered in the ISRCTN registry ISRCTN11974930, registered on 25 June 2026.