This calming, tasty smoothie recipe contains bananas, which are a good source of B-6, a precursor to melatonin production in the body. Melatonin is a hormone that regulates circadian rhythms (our sleep-wake cycles). Kale and milk are both good sources of calcium. A calcium deficiency may contribute to insomnia. Tart cherry juice was shown in a study to aid in sleep because it also contains melatonin. This smoothie recipe combines all of these natural sleep-inducing ingredients while providing a slightly tart but sweet bedtime treat. Try it with sweet cherry juice in place of the tart juice for a mellower flavor.