P2B345: Novel Infant Formula Enriched with Alpha-lactalbumin Increases Available Tryptophan and Improves Sleep Outcomes

Background: Sleep is crucial during the first year of life. Tryptophan, as a precursor to serotonin, is influential in the sleep-wake cycle, and studies in infants and adults have shown that increasing tryptophan intake can improve sleep outcomes. Tryptophan must pass through the blood-brain barrier in competition with other large neutral amino acids (LNAA). Therefore, the ratio of tryptophan to LNAA functions as an indicator of brain tryptophan concentrations. Alpha-lactalbumin has the highest tryptophan to LNAA ratio of all food-derived proteins. Consumption of alpha-lactalbumin increases ratios of tryptophan to LNAA and may improve sleep outcomes. Given these findings, it was hypothesized that the enrichment of a novel infant formula with alpha-lactalbumin would improve sleep outcomes.

Methods: Healthy term infants were randomized to receive either the study formula (ByHeart, Inc.) enriched with alpha-lactalbumin (SF) or an isoenergetic formula with identical total protein content without alpha-lactalbumin enrichment (CF). Three-day formula intake records were completed every 4 weeks for 24 weeks. Parents reported date, start time of each feed, and amount consumed for 3 consecutive 24-hour periods. Blood was drawn at 16 weeks of life in a subgroup of infants without any complementary food intake, and serum amino acids were analyzed. The ratio of tryptophan to large neutral amino acids (including leucine, isoleucine, valine, tyrosine, phenylalanine) was calculated and compared between SF and CF using Wilcoxon rank-sum test. Repeated measures mixed models with an unstructured covariance matrix were fit with continuous outcome and study group, visit and their interaction as predictors, adjusted for sex, age at enrollment and site to evaluate number of night feedings and time between feeds.

Results: 128 infants were included in the sleep analyses, and a subgroup of 49 infants were included in the amino acid analysis (21 in the SF group, 28 in the CF group). At 16 weeks, the number of night feeds was lower in the study formula group versus the comparator formula group (mean 1.2 versus 1.5, mean difference -0.3 (95% CI: -0.6, 0.0); p=0.04). For time between feeds, significant group differences were observed at week 16, where the time between feeds was greater in the study formula group versus the comparator formula group (18 minutes (95% CI 0, 35), p=0.04). The ratio of tryptophan to LNAA concentration was higher in the SF group (0.146 ± 0.026) compared to the CF group (0.130 ± 0.018; p= 0.007). There was a significant positive correlation between tryptophan:LNAA ratio and time between feeds at week 16 (Pearson correlation ρ=0.42, p=0.004; n=45).

Conclusion: At 16 weeks, infants who consumed the study formula, enriched with alpha-lactalbumin, had a higher tryptophan:LNAA ratio, indicating more available tryptophan. Clinically, these infants had significantly fewer nighttime feeds and a longer duration between feeds, possibly indicating improved sleep quality.