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  • Consumption of mg day of caffeine was

    2018-10-26

    Consumption of <100mg/day of caffeine was recorded in 320 (45%) participants, from 100 to 200mg/day in 299 (42%), and >200mg/day in the remaining 97 (13%). The main source of caffeine intake was coffee, which was most often consumed early in the morning and in the late afternoon. Overall, 115 (16%) individuals admitted daily ingestion of ≥2 cups of coffee, 267 (37%) between 1 and 2 cups, 147 (21%) less than one, and the remaining 187 (26%) reported no intake of coffee at all. Second in importance were caffeine-containing soft-drinks (consumed by 67% of the population). Energy drinks were eventually consumed and only by men during working hours, while chocolate (often with milk) was a preferred beverage for women during or after dinner. Consumption of black tea was reported by less than 5% of the population and was irrelevant to the average amount of caffeine intake in most cases. The intake of caffeine-containing pills (pain relievers) was also uncommon and irrelevant for the main findings. Characteristics of participants across categories of caffeine intake and sleep quality are summarized in Table 1. In univariate analyses, depression was the single variable significantly associated with higher amounts of caffeine intake. On the other hand, individuals with poor sleep quality were older, less educated, reported worse physical activity and had more often symptoms of depression than those with good sleep quality. An exposure logistic regression model showed significant association of the amount of caffeine intake with symptoms of depression (p=0.031) and total cholesterol blood levels (p=0.042), and a marginal association with smoking status (p=0.061). A generalized lineal model showed significant association of sleep quality (continuous PSQI score) with age (p<0.001), symptoms of depression (p<0.001) and physical activity (p=0.009), and marginal association with fasting gingerol levels (p=0.069). The exposure-effect model, adjusted for relevant confounders, revealed no effect of caffeine intake on sleep quality (average exposure effect: 0.027, 95% C.I.: −0.284 to 0.338, p=0.866).
    Discussion This population-based study shows that caffeine intake has no effect on sleep quality in community-dwelling adults living in a quiet rural village of Ecuador. As previously noted, the effect of caffeine intake on sleep quality at the population level has been scarcely investigated and, to our knowledge, there is only one study in 181 community-dwellers showing no relationship between these variables [17]. The assessment of the effect of caffeine intake on sleep quality at the population level may be complicated by personal experiences of gingerol given individuals, as it is possible that those who think are “sensitive to coffee” avoid this substance at night. In the present study, however, we quantified the total amount of caffeine intake from sources other than coffee. A 500ml bottle of Pepsi© or Coca-Cola© (the most commonly consumed soft drinks in the village) contain more than 40mg of caffeine, which if consumed at dinner, would be enough to keep plasma caffeine concentrations over the night. In Ecuador, labels of these soft drinks just mention their caffeine, but there is no additional information about the amounts of milligrams per serving. Caffeine half-life has been estimated to be about six hours but wide variability exists among individuals, and it is known to be modified by age, alcohol intake, pregnancy, liver failure and several other conditions and diseases [18–20]. Moreover, it has been shown that residual caffeine in concentrations enough to be associated with poor sleep quality, may be detected in saliva up to 16h after a single 200mg dose of coffee [21]. Therefore, assessment of day-long consumption of caffeine should not be seen as a major limitation of the present study. Nevertheless, further studies should formally investigate differences between morning and late afternoon caffeine intake in sleep quality to confirm this assumption.