Sleep-inducing effect of lettuce (Lactuca sativa) varieties on pentobarbital-induced sleep

The objective of this study was to investigate the sleep-inducing effect of lettuce varieties and the extracts derived from romaine lettuce on pentobarbital-induced sleep. Romaine lettuce had a higher lactucin content (red romaine: 361.50 µg/g of extract, green romaine: 1071.67 µg/g of extract) compared to the green and red lettuce varieties. The seed and leaf extracts derived from romaine lettuce induced an increase in the sleep duration at low and high doses respectively. The seed extract of romaine lettuce showed higher content of polyphenols, including caftaric acid, chlorogenic acid, and chicoric acid, compared to the leaf extract. The IC₅₀ value of the leaf extract for its DPPH radical-scavenging was significantly less (0.11 mg/mL) than that of the seed extract (0.21 mg/mL) (p < 0.05). Romaine lettuce is an interesting and valuable source of sleep potentiating material and contains antioxidant phenolics that protect from the oxidant stress caused by sleep disturbance.