Changes in circulating concentrations of vitamins and trace elements after cessation of nocturnal enteral tube feeding.
BACKGROUND: This study aimed to examine whether circulating concentrations of a range of vitamins and trace elements in patients receiving long-term cyclic enteral tube feeding vary during the day, and whether standardised time points for blood sampling are required for assessment of nutrient status. METHODS: Circulating concentrations or activities of water-soluble vitamins (thiamine, riboflavin, and vitamins B6, B12, folate and C), fat-soluble vitamins (A, D, E) and trace elements (iron, zinc, copper and selenium (assessed by glutathione peroxidase activity), were measured at 0,3,6 and 9-12h after cessation of nocturnal feeding (fasting), in eight clinically stable patients receiving cyclic nocturnal enteral nutrition. RESULTS: The circulating concentrations of the nutrients did not change between the fed and fasted state (repeated-measures-ANOVA) except the following: plasma folate increased progressively from 10.9 (SD 4.6)nmol/l in the fed state to 14.0 (SD 4.4)nmol/l at 9-12 h after cessation of feeding (P<0.05); plasma zinc increased progressively throughout the fasting period by 33.5% (8.57, SD 0.68 vs. 11.44, SD 1.85 micromol/l, in fed state vs. 9-12h fast respectively, P<0.05); and total tocopherol/cholesterol ratio decreased by 9.6% during the study period (P<0.02), while gamma-tocopherol increased by 59.2% (P<0.05). For all analytes, the concentrations in blood samples taken at 3 and 6h after cessation of feeding were not significantly different from those at 9-12h. CONCLUSIONS: Although cessation of nocturnal tube feeding had no significant effect on the circulating concentrations of most micronutrients, it increased plasma folate and zinc concentrations, and decreased the tocopherol/cholesterol ratio. The timing for blood sampling should be standardised when the status of these nutrients is assessed in patients receiving cyclic tube feeding.