Population-level data linking short sleep to obesity.
What the evidence says
- Systematic review of 36 studies: short sleep associated with higher body weight — strong and consistent in children (all 11 cross-sectional studies positive) and in all three adult longitudinal studies, but the review calls the adult cross-sectional results ”more mixed” (17 of 23). The authors state plainly that whether the relationship is causal is undetermined[1]
- Dose-response in children: Japanese cohort (n=8,274) — <8h OR=2.89, 8-9h OR=1.89, 9-10h OR=1.49 vs ≥10h[1]
- Longitudinal adult evidence: Nurses Health Study (n=68,183, 16 years) — ≤5h → 1.14 kg greater gain, obesity HR=1.15, ≥15 kg gain HR=1.28 vs 7h baseline[1]
- Relationship appears to weaken with age: Zurich cohort (13 years) — <6h at age 27: OR=7.4; at age 40: OR=1.1[1]
- Mechanisms: sleep curtailment decreases leptin, elevates ghrelin, increases hunger especially for high-fat/high-carb foods[1]
- Important caveat: Zurich study found weight was a better predictor of future sleep than sleep was of future weight — reverse causation is plausible[1]