As a holistic nutritionist, I often work with people who have trouble sleeping. Some wake throughout the night; others jolt up at two a.m. and are unable to return to sleep; others can’t fall asleep. These are people in decent shape, who exercise and eat healthful diets.

They’ve tried top-down solutions: eye masks and earplugs, herbs like hops and valerian, the “sleepy” amino acids GABA and tryptophan, and tablets of melatonin, the sleep hormone. I try to help clients resolve the underlying causes of sleeplessness. Which remedy works best depends on the individual, because the causes of…