Association between iron intake and excessive daytime sleepiness in the community-dwelling Japanese: the Toon Health Study.

Purpose: Brain iron deficiency is known to cause dopaminergic dysfunction in people with restless legs syndrome. Considering the role that dopamine plays in the wake-promoting system, we speculated that iron deficiency may contribute to the development of excessive daytime sleepiness (EDS). Therefore, we conducted the present study to examine the association between iron intake and EDS in the general population.

Methods: We collected data from the participants of the Toon Health Study from 2009 to 2017 (N = 2405) and conducted a cross-sectional analysis. EDS was defined as an Epworth Sleepiness Scale score ≥ 11. Participants were divided into four groups according to quartiles of estimated iron intake from their responses to the Food Frequency Questionnaire. We used sex, age, body mass index, and sleep duration as adjustment variables.

Results: The mean age of the participants was 57.9 years, and 64.2% were women. Compared to the highest quartile of iron intake, the multivariable-adjusted odds ratio for EDS of the lowest quartile was 1.38 (95% confidence interval [CI]: 1.04-1.83, p for trend = 0.03). When the analysis was restricted to participants with a Pittsburgh Sleep Quality Index (PSQI) score < 6, the odds ratio was 1.57 (95% CI: 1.06-2.31, p for trend = 0.04).

Conclusions: Significant inverse associations were observed between iron intake and EDS. This tendency was also observed in participants without substantial subjective sleep disturbance (i.e., PSQI score < 6), suggesting that iron deficiency may play a role in the wake-promoting system independently of sleep disturbances.