“…The results reveal the absence of a causal relationship between genetically determined variations in 25(OH)D levels and the risk of PPD. While a majority of available observational studies, often employing cross-sectional or case-control designs, have reported there exists an inverse correlation between the levels of 25(OH)D and postpartum depression [ 22 , 23 ], some studies have failed to establish a significant association between 25(OH)D levels and the occurrence or development of PPD [ 24 , 25 ]. Indeed, the true nature of the relationship between PPD and 25(OH)D remains unclear due to confounding factors and potential reverse causation.…”