Evaluation of carnitine nutritional status in full-term newborn infants

Carnitine supplements may be advisable not only in premature but also in artificially-fed full-term babies. The acyl-carnitine/free carnitine (AC/FC) and FC/total carnitine (FC/TC) ratios have been considered markers of "carnitine insufficiency" and "carnitine deficiency", respectively. Values of AC/FC>0.40 are considered abnormal and mean that FC has a low bioavailability to the cells and so reflects a "carnitine insufficiency". Values of FC/TC<0.7 indicate "carnitine deficiency". We analyze the validity of such ratios and the limits for them in three groups of full-term neonates (n=66): 22 breast-fed (BF), 22 with formula (F); and 22 fed with carnitine-supplemented formula. Several studies have shown the need to give supplements of carnitine to the neonate because of its "essentiality", but no one has demonstrated the adequate dosages. We therefore propose to establish new limit levels for these ratios to control carnitine nutritional status in neonates, based on the control of percentile ranges for normal BF infants (in this study: 97th percentile of AC/FC>0.83; 3rd percentile of FC/TC<0.54) and on evaluating the needs of neonates and dosages required to supplement F. The supplement of 2.2 mg of L-carnitine/100 ml in the cow's milk formula used in the present study produces a similar biochemical pattern of plasma carnitine and ACs to that observed in BF infants, together with a lower risk of developing "carnitine deficiency" or "carnitine insufficiency" than those babies fed with nonenriched F. Considering that human milk is the best source of nutrition for full-term infants, the limit established for AC/FC and FC/TC ratios at other ages of life seems to be "inadequate" for neonates.