Sleep duration and reported functional capacity among black and white US adults

Evidence suggests that individuals reporting sleeping below or above the population's modal sleep duration are at risk for diabetes, hypertension, and other cardiovascular diseases. Evidence also indicates that individuals with these conditions have reduced functional capacity. We assessed whether reported sleep duration and functional capacity are independently associated and whether individuals' race/ethnicity has an effect on this association.

Data were obtained from 29,818 black and white Americans (age range: 18-85 years) who participated in the 2005 National Health Interview Survey (NHIS). The NHIS uses a multistage area probability design sampling of non-institutionalized representatives of the US civilian population. Of the sample, 85% were white and 56% were women.

Univariate logistic regression analysis showed that individuals sleeping < 6 h were 3.55 times more likely than those sleeping 6-8 h to be functionally impaired (34% vs 13%; p < 0.001). Likewise, those sleeping > 8 h were 3.77 times more likely to be functionally impaired (36% vs 13%; p < 0.001). Individuals of the black race/ethnicity were more likely to be functionally impaired than their white counterparts (23% vs 19%; p < 0.001). Multivariate-adjusted regression analyses showed significant interactions between individuals' race/ethnicity and short sleep with respect to functional capacity (black: OR = 2.78, p < 0.0001; white: OR = 2.30, p < 0.0001). Significant interactions between race/ethnicity and long sleep were also observed (black: OR = 2.43, p < 0.001; white: OR = 2.63, p < 0.001).

Our findings suggest that individuals' habitual sleep duration and their race/ethnicity are significant predictors of their functional capacity.