Comparison of Vitamin Concentrations in Tears and Serum

Results obtained during a recent study suggest that tears could be used as specimens to monitor nutritional health, since they are easily obtained, sufficiently mirror blood serum data, and enhance the speed of deficiency diagnoses.

Investigators at Michigan Technological University obtained matched samples of tears and serum from 15 family pairs, each pair consisting of a four-month-old infant - fed either liquid formula or mother's milk - and one parent.

Several water-soluble and fat-soluble vitamins were detected and their levels were quantified by liquid chromatography/mass spectrometry. Vitamin concentrations were compared between tears and blood serum for individual subjects, between infants and parents, and against self-reported dietary intakes.

They investigators reported that water-soluble vitamins B1, B2, B3 (nicotinamide), B5, B9 and fat-soluble vitamin E (alpha-tocopherol) were routinely detected in tears and blood serum while fat-soluble vitamin A (retinol) was detected only in blood serum. Water-soluble vitamin concentrations measured in tears and blood serum of single subjects were comparable, while higher concentrations were measured in infants compared to their parents.

Strong positive correlations were found between tear and blood serum concentrations of vitamin E from infants and parents and vitamin B3 concentrations from parents, while slight positive correlations were detected for infants B3 and parents B1 and B2 concentrations. Correlations between infants and parents were found for the concentrations of B1, B2, B3, and E in tears, and the concentrations of B2, A, and E in blood serum. Stronger vitamin concentration correlations were found between infants and parents for the breast-fed infants, while no significant difference was observed between breast-fed and bottle-fed infants.

"Our goal was to seek the viability of establishing measurable units of tears for nutritional assessments," said first author Dr. Maryam Khaksari, mass spectrometry research specialist at Michigan Tech University. "Your body cannot manufacture vitamins, and vitamins reflect available food sources in your body. That is what makes them good indicators of nutritional health. Since tears contain vitamins, they might have real potential to replace other clinical tests."

The study was published in the December 23, 2016, online edition of the journal Experimental Eye Research.