In this analysis of 27 983 women, we identified distinctive eating patterns that were associated with sleep duration. Compared with women with normative sleep duration (7–7·9 h daily), short sleep duration and, to a lesser extent, long sleep duration were both associated with reduced tendency for eating during conventional eating hours and greater degree of snack dominance over meals.
Eating during unconventional hours (i.e. before breakfast and after bedtime) may reflect accommodations made to adjust to short sleep duration. In our exploratory analysis, short sleepers tended to go to bed later than those with normative sleep duration, thereby having more opportunities for eating at later hours. Furthermore, staying awake at night alone may also lead to physiological changes that promote hunger. In an experimentally controlled study, those who stayed awake later at night had lower concentrations of the anorexigenic hormone leptin without a notable peak at night compared with subjects who were asleep by 22.30 hours(16)
. Likewise, women with short sleep duration also tend to get up early and are more likely to replace breakfast with an early morning snack, supported by the previous findings of a higher prevalence of skipping breakfast in persons with short sleep duration (16)
. Given that the preceding meal largely determines the size and the time of the following meal(25)
, substitution of breakfast with an early morning snack could subsequently affect eating patterns throughout the day. Thus, greater snack dominance over meals observed in habitual short sleepers may represent deviations in eating patterns arising from early rising or late bedtime.
The present study also showed that the eating patterns prevalent among short and long sleepers were reflective of a nutritionally poor diet; both eating during unconventional eating hours and preponderance of snacks over meals were related to lower intakes of fruits and vegetables and higher intakes of sweets and fat as a percentage of energy.
Snacks are generally composed of foods with higher carbohydrate and lower protein, and frequent snacking was found to be a good predictor of nutritionally empty and energy-laden diet in a previous study(13)
. On the other hand, breakfast often consists of foods with low fat and high carbohydrate and fibre contents(26,27)
, and skipping breakfast is considered to lead to intake of compensatory snacks with relatively poor nutritional quality or overeating in later meals(27)
. Compared with individuals who regularly eat breakfast, those who skip breakfast had a lower micronutrient intake, a higher energy intake from fat and a higher level of LDL cholesterol(27,28)
Night-time eating also has been positively correlated with fat, carbohydrate and total energy intakes(29)
, and has been more commonly reported in obese women than among non-obese women(30)
. Moreover, food intake at a later time of day may induce different physiological responses to food: it has been suggested that food intake in the evening or night is more likely than food consumed at other times of the day to preserve glycogen levels in muscles, ultimately leading to higher adiposity(31)
Some limitations of the present study should be acknowledged. First, our participants were volunteers. As in other volunteer populations, compared with the general US population, they were more educated and had higher incomes on average, which might limit the external generalizability of our results. However, the associations between sociodemographic factors and sleep duration observed in our study were similar to those from the National Health Interview Survey(32)
, suggesting that, at least in terms of sleep duration, our participants are comparable to a nationally representative US sample.
Second, there have been no established approaches to define what constitutes a ‘meal’ v
. a ‘snack’(33)
. In the present study, ‘snack’ was loosely defined as an eating episode between meals except for non-caloric drinks and no clear definition of ‘meal’ was provided; thus, number, size and timing of ‘meals’ may be subject to individual variations in sociocultural norms and chronological trends(33)
. However, we were unable to evaluate the impact of such misclassification on the present findings.
Finally, although it was assumed that sleep duration was a prior event influencing eating patterns, we recognize that the relationship between sleep duration and eating patterns is likely to be bidirectional. Data suggest that sleep loss alters physiological regulation of metabolic hormones, which not only influences diet and eating patterns but also feeds back to affect the sleep–wake regulatory process itself(9)
. Conversely, it is also possible that short sleep duration and the associated eating patterns may be a manifestation of either genetically or non-genetically altered circadian rhythms(9)
. Mice with mutations in the clock
gene that disrupt cellular rhythmicity showed a significant increase in energy intake and body weight, and higher levels of leptin and glucose, compared with wild-type mice(15)
. In man, polymorphisms in the clock
gene have been associated with sleep deregulation(34)
In conclusion, our data show that short and very long sleep duration are associated with eating during unconventional eating hours and snacking. Combined with growing evidence indicating circadian variation in physiological responses to foods(31)
, these results suggest that disrupted eating patterns may exacerbate the development of obesity and metabolic diseases in habitual short and very long sleepers via poor nutritional composition and altered physiological responses to nutrients.