Protein intake and its association with sleep quality: results from 3 prospective cohort studies

Sleep quality is a critical factor for daytime functioning and chronic disease risk. We investigated the association between intakes of total protein and protein subtypes and sleep quality in three U.S. cohorts. In the Nurses’ Health Study (NHS), NHS2, and Health Professionals Follow-up study (HPFS), dietary intake was assessed every 4 years using validated food frequency questionnaires. Sleep quality was measured once with the Pittsburgh Sleep Quality Index or adapted versions. With ordinal logistic regression, odds ratios (OR) and 95% confidence intervals (CI) were calculated to estimate the odds of having better sleep quality versus poorer sleep quality depending on protein intake (%Energy) based on the average of the prior two dietary questionnaires. In 32,212 women from NHS, 51,126 women from NHS2, and 14,796 men from HPFS, total protein intake was not associated with sleep quality. However, the intake of protein from vegetable sources showed no association or a positive association with sleep quality (OR for quartile 4 versus quartile 1 in NHS: 1.12, 1.04–1.20, P-trend < 0.001; NHS2: 1.01, 0.95–1.07, P-trend = 0.90; HPFS: 1.11, 0.99–1.23, P-trend = 0.05), whereas divergent results were observed for animal protein sources. Overall, intakes of processed red meat and poultry were associated with worse sleep quality, whereas no or positive associations were observed for dairy and fish protein. Our results suggest that plants as a source of protein may be associated with better sleep quality than animal sources of protein. Further studies are warranted to validate our findings.