To the Editor: In their cohort study assessing the relationship between sleep duration and incident coronary artery calcification, Mr King and colleagues1 reported an association between longer sleep duration and reduced incidence of coronary artery calcification. The proportion of individuals who developed coronary calcification was markedly greater among participants with actigraphy measurements indicating sleep duration of less than 4 hours per night (measured for 6 nights for each participant).
For many persons, it is difficult to maintain sleep duration of less than 4 hours per night without ingestion of stimulants such as caffeine. Heavy use of caffeine among these participants may have confounded the study results. The relationship between consumption of coffee (the primary source of caffeine in the United States) and coronary risk is controversial. Some studies suggest a U-shaped or J-shaped association between coffee consumption and coronary artery disease.2
Those achieving less than 4 hours of sleep per night may represent individuals who ingest extraordinarily large amounts of caffeine beyond the range of harmless consumption. In controlled studies, caffeine has been shown to adversely affect measures associated with development of coronary artery disease, such as increased aortic stiffness3 and blood pressure.4 The only study to assess coffee consumption and coronary artery calcification reported a protective association in older women but not men.5 The strongest association was observed in women consuming 375 to 500 mL per day. However, the study was not powered to detect a relationship between heavy coffee consumption and coronary artery calcification. Furthermore, coffee may have cardioprotective constituents that are not present in other commonly consumed caffeinated beverages.
Because it is plausible that high consumption of caffeine in those sleeping less than 4 hours per night may have contributed to coronary artery calcification, we suggest that the amount and source of caffeine be assessed in future studies that explore the relationship between sleep and coronary artery calcification.
Financial Disclosures: None reported.
Country-Specific Mortality and Growth Failure in Infancy and Yound Children and Association With Material Stature
Use interactive graphics and maps to view and sort country-specific infant and early dhildhood mortality and growth failure data and their association with maternal
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