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Natural Abundance of 13C in Serum Retinol Differentiates Between Dietary Intakes of C3 versus C4 Plants

Sherry A Tanumihardjo*

Vitamin A is a micronutrient essential in vision, reproduction, immune function, and cellular differentiation. ProvitaminA carotenoids are plant sources of vitamin A. The isotopic distribution of 13C and 12C in humans is determined by what foods are consumed. C3 plants, i.e., green vegetables, carrots, and pumpkins, have lower 13C:12C than C4 staple crops, i.e., maize, sorghum, and millet. Vitamin A foods from corn-fed animals will reflect the13C:12C feed that the animals eat. The serum retinol13C:12C was previously evaluated as a biomarker for vegetable intake. The retinol13C:12C decreased in humans who increased their vegetable intake (range -26.21 to -31.57‰, P = 0.050) and correlated with provitamin A carotenoid intake (P = 0.079). The average δ difference was -0.526 with increased vegetable intake, while control increased by +0.370.A 2X2X2 study in Mongolian gerbils fed white and orange maize or carrots for an extended period of time.Serum retinol δ13C‰ differentiated between those consuming white maize and white carrots (–27.1±1.2 δ13C‰) from those consuming orange maize and white carrots (-21.6±1.4 δ13C‰, P<0.0001) and white maize and orange carrots (-30.6±0.7 δ13C‰, P<0.0001). This method was applied to Zambian children who had been fed either orange or white maize for two months. Those children who consumed orange maize had a lower δ13C‰ (-26.64±1.98) than their white maize-consuming counterparts (-27.39±1.94) (P = 0.049). In the application of this methodology to efficacy or effectiveness trials, it will be important to choose the appropriate control group and number of subjects for comparison analyses.

Objectives: We investigated changes in serum retinol relative differences of isotope amount ratios of 13C/12C (∂13C) caused by natural 13C fractionation in C3 compared with C4 plants as a biomarker to detect provitamin A efficacy from biofortified (orange) maize and high-carotene carrots.