Dietary and plasma retinoids are not associated with fatty acid desaturase indices in healthy young adults

Past research in rodents suggests that fatty acid (FA) desaturase expression and activity may be modified by vitamin A; however, this has not been investigated in humans. The primary objective of this study was to examine associations between dietary retinoid intakes, plasma retinoid concentrations, and FA desaturase indices in young adults. As a secondary objective, biological sex and estrogen-containing contraceptive (EC) use were investigated due to prior evidence demonstrating that both can influence plasma retinol concentration and FA desaturase indices. Dietary retinoid intake (food frequency questionnaire), plasma retinoid concentrations (high-performance liquid chromatography–tandem mass spectrometry), plasma FA (gas chromatography), and FA desaturase indices (product-to-precursor ratios) from 945 adults recruited for the cross-sectional Toronto Nutrigenomics and Health study were analyzed. Participants were stratified into quartiles based on plasma retinol concentration and data analyzed by one-way analysis of covariance. Dietary retinoid intakes were not associated with the overall n-3 pathway, overall n-6 pathway, delta-5 desaturase, delta-6 desaturase, or delta-9 desaturase indices (all r < 0.10, p > 0.05). The overall n-6 pathway index was significantly higher (p = 0.0004) and the delta-5 desaturase index was significantly lower (p = 0.0003) in individuals with higher plasma retinol levels; however, these differences were lost when participants were grouped by biological sex and EC use. Although weak relationships were observed between plasma retinol and some FA desaturase indices in the total population, these associations appear to be driven by biological sex and EC usage rather than retinoids. We therefore find little evidence of a relationship between retinoids and FA desaturase indices in young, healthy adults.