You bought collagen for your skin, but a new scoping review asks whether its glycine might also help you sleep. Glycine supplements reliably raise blood glycine, and all three glycine sleep trials found a benefit on at least one outcome. Collagen peptides showed fewer awakenings in one placebo-controlled trial and lower fatigue in another, yet failed to beat alpha-lactalbumin in head-to-head comparisons. Nobody has tested whether glycine is actually the mechanism. Here's the dose, the timing, and the limits you should know.
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