Smartphone use is associated with later and shorter actigraphic sleep, and circadian clock delays in an indigenous Toba/Qom community

Smartphones are integral to modern life, yet their influence on sleep and circadian rhythms are not fully understood, partly due to the many confounding factors in industrialized settings. The Toba/Qom from northern Argentina, a preindustrial group in which smartphones have only been introduced recently, offer a natural experiment to study the role of these devices in modulating biological rhythms and sleep. We recorded sleep through longitudinal wrist actigraphy from 100 participants in three Toba/Qom communities (age range = 12-49 y.o., 54% females) for 30-60 days at five different points between October 2023 and June 2025. The analysis of 8,407 actigraphic sleep events revealed that smartphone users (61-82% across data collection campaigns) exhibited a later sleep onset (+13 min, 95%CI [6, 20], p < .001) and a shorter sleep duration (-22 [-29, -14] min, p < .001) than non-users. This delay was supported by two mechanisms: 1) a physiological sustained shift, evidenced by a later dim-light melatonin onset in smartphone users (+34 [6, 62] min, p = .017); and 2) an acute nightly pattern, as users displayed later sleep acutely on nights on which they reported using their smartphones at bedtime (+12 [2, 21] min, p = .016). These findings confirm that smartphone-related sleep disruption is a multifaceted phenomenon involving both circadian physiology and behavioral changes. By focusing on an indigenous population slowly acquiring industrialized-world features, this study offers rare insight into the impact of digital integration on sleep health, with implications for human physiology and psychology.