Association of greenness exposure with serum vitamin D status and effects of ambient particulate matter among pregnant women in early pregnancy.

Adequate vitamin D is essential for the health of both the mother and fetus, and it can be influenced by environmental factors. However, research on the associations between greenness exposure and vitamin D concentrations during pregnancy is limited. This retrospective birth cohort study, conducted from 2014 to 2018, assessed the greenness of residences using the satellite-derived normalised difference vegetation index (NDVI). Serum 25-hydroxyvitamin D [25(OH)D] concentrations were categorised as non-deficient (≥50 nmol/L) or deficient (<50 nmol/L). Multiple log-binomial regression models were used to estimate the association of NDVI with serum 25(OH)D concentrations and vitamin D deficiency (VDD). Subgroup and mediation analyses were conducted to estimate the association of ambient particulate matter (PM) on the association between NDVI and VDD. A total of 64,663 pregnant women with a mean maternal age of 30.6 (standard deviation: 3.86) years were included. 250-m NDVI was negatively associated with the risk of VDD (per 0.1-unit increase, relative risk [RR]: 0.98, 95 % CI: 0.97-0.99). With the highest quartile of NDVI exposure as the reference group, the upper-middle quartile (RR: 1.02, 95 % CI: 1.00-1.03), and lowest quartile (RR: 1.03, 95 % CI: 1.01-1.06) had an increased risk of VDD. At higher PM exposure concentrations, 250-m NDVI exposure was negatively associated with the risk of VDD (RR: 0.98, 95 %CI: 0.97-0.99, per 0.1-unit increase), but not at lower PM exposure concentrations. Among pregnant women with higher PM, the mediation of PM exposure on the association between 250-m NDVI and VDD was 44.70 % (P = 0.0116). Among pregnant women with higher PM exposure, the mediation of PM exposure on the association between 250-m NDVI and VDD was 17.98 % (P = 0.002). These findings suggest that higher residential greenery significantly reduces the risk of VDD in pregnant women, particularly in those exposed to increased PM concentrations.