H R Lieberman et al, 2019. Demographics, Sleep, and Daily Patterns of Caffeine Intake of Shift Workers in a Nationally Representative Sample of the US Adult Population, Sleep, published online.

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ABSTRACT

STUDY OBJECTIVE:
Caffeine is the most widely consumed stimulant in the world and sociodemographic factors including occupation are associated with intake. Shift work, required in various occupations, is associated with poor sleep, inadequate diet, and adverse health effects. Using a large nationally-representative database, demographics, sleep, and caffeine intake of US adults working various shifts were assessed.

METHODS:
The 24-hour dietary recall data from NHANES 2005-2010 (N=8,500) were used to estimate caffeine intake from foods and beverages. Work shifts were self-reported as: regular day-shift; evening-shift; night-shift; rotating-shift; or other-shift. Regression analyses assessed associations of shift work with caffeine intake after adjustment for sociodemographic factors.

RESULTS:
Approximately 74% of employed adults were day-shift workers and 26% were non-day shift workers. Night-shift workers slept for 6.25±0.09 hours per day, somewhat less than day-shift workers who only slept 6.83±0.02 hours (P<0.0001). Mean 24-hour weekday caffeine intake of evening-, night-, and rotating-shift workers (217±23, 184±19, and 206±15 mg, respectively) was similar (P>0.3) to day-shift workers (203±5 mg). Regardless of work schedule, individuals consumed the most caffeine during morning hours. Evening and night-shift workers reported consuming 36-46% less caffeine during their work hours and 72-169% more during non-work hours than day-shift workers. (P<0.01).

CONCLUSIONS:
Total daily caffeine intake of shift workers is similar to non-shift workers; most caffeine is consumed in the morning regardless of shift. Since shift workers consume less caffeine during regular work hours and more during non-work hours than day workers, they may be using caffeine to, in part, optimize off-duty alertness.

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