[Trace nutrients in total enteral nutrition: the basal status and longitudinal course]

Previous studies demonstrated deficiencies of selenium and other micronutrients in patients receiving total enteral nutrition (TEN). The content and bioavailability of trace elements in enteral formulas can be suboptimal.

Basal blood levels of some trace elements (copper, iron, selenium, zinc) and vitamins (B12, folic acid) were determined in twenty patients at the beginning of TEN. Vitamin E was measured in 7 patients. Primary diagnosis was cancer (no. = 13) and organic brain syndromes (no. = 7). Commercially available polymeric and oligomeric enteral formulas were used, containing respectively, as a percent of RDA in 1500 kcal, 65-39% of copper, 180-135% of iron, 80-100% of zinc. Selenium was not indicated; determinations in our laboratory gave a content of 78-63% of the minimum recommended intake. Blood levels of copper and zinc (no. = 6), selenium (no. = 5), iron, transferrin and ferritin (no. = 13) were measured after two months of TEN (mean intake of 30 +/- 3 kcal/kg/day). Copper, selenium and zinc were measured with atomic absorption; iron with the complessometric method: vitamin B12 and folic acid with RIA; vitamin E with HPLC.

Mean values, expressed as mean +/- SD (range) were: copper: 129 +/- 23 (82-300) micrograms/dl; iron: 37 +/- 18 (16-89) mg/dl; selenium: 53 +/- 20 (22-93) micrograms/dl; zinc: 85 +/- 34 (44-185) micrograms/dl; vitamin B12: 632 +/- 450 (140-1575) pg/ml); vitamin E: 5.4 +/- 1.5 (3.3-7.8) mg/dl; folic acid: 11 +/- 8 (2-20) ng/ml. Values below the lower normal limit were found in 100% (vitamin E), 89% (selenium), 60% (iron), 35% (zinc), 24% (vitamin B12) and 14% (folic acid) of the patients studied. Copper was higher than the upper normal limit in 31% of cases; no data below normal range was found. Mean blood levels of depleted subjects were at the 28%, 43%, 54% and 63% of the mean normal value respectively for iron, selenium, vitamin E and zinc. Blood iron (p < 0.05) and selenium (p < 0.001) were significantly lower in more malnourished patients (weight loss > 20% vs < 20% on usual body weight). After two months of TEN, a reduction of 33% of mean blood selenium was observed in 4 of 5 patients studied. Blood copper and zinc remained stable in 6 subjects with initial normal or higher than normal values. Blood iron increased nonsignificantly, ferritin remained stable, transferrin increased significantly (p < 0.05). No clinical deficiency syndromes were observed.

A careful monitoring of micronutrients during TEN is recommended. Selenium content of enteral formulas, unless supplemented by the producers, seems to be insufficient to maintain the initial blood level in two months of TEN.