To the Editor:
Bansi et al.1 mentioned that combinations of sleep disorders, short sleep duration and quality of sleep were associated with increased risk in the prevalence of hypertension. Cappuccio et al.2 conducted a systematic review and meta-analysis for the effect of sleep duration on cardiovascular diseases. They could not evaluate sleep disorders and quality of sleep simultaneously because of the lack of information. Appropriate sleep duration differs from person to person, and I suppose that there is no standard or reference value for sleep duration to predict human health. Furthermore, obstructive sleep apnea syndrome (OSAS) is a risk factor of hypertension,3 and OSAS and hypertension interact on arterial stiffness.4 Taking together, selection of parameters is important for risk assessment of hypertension. On this point, Bansi et al.1 conducted appropriate research using several sleep parameters simultanelously.
By the way, Fernandez-Mendoza et al.5 reported that anxiety and lack of stress coping accelerated the underestimation of objective sleep duration by sleep polygraphy among insomniacs. This means that sleep disorders, sleep duration and quality of sleep should be evaluated in combination with mental status. The author presents here the association between sleep duration and depressive state by considering perceived sleep quality (refreshment by sleep).
The target subjects were employees of a company in Japan. Age of the subjects ranged from 20 to 60 and the number of subjects was 117 (113 males and four females). Simple summation of each item score (0–3) for Patient Health Questionnaire nine-item version (PHQ-9)6 was adopted in this study. Sleep duration was categorized as follows: (I) under 5 h, (II) 5–6 h, (III) 6–7 h, and (IV) 7 h or more. Refreshment by sleep was declared binary as “Yes” or “No.”
Percent of refreshment by sleep stratified by four categories of sleep duration (I to IV) were 0%, 22.2%, 76.2% and 100%. In 62 subjects who replied “refreshment by sleep” as “No,” the age-adjusted means and standard errors of PHQ-9 stratified by categories of sleep duration (I to III) were 10.2±1.37, 5.3±0.78, and 6.8±1.66, respectively. There was a significant difference in the mean value of PHQ-9 between group I and group II by multiple comparison (P<0.05).
In contrast, there was no significant difference in the mean value of PHQ-9 among three groups who declared positive answer on “refreshment by sleep” (n=55). The means and standard errors of PHQ-9 with adjusted age stratified by three categories of sleep duration (II to IV) were 5.4±1.19, 2.7±0.74, and 4.7±1.19, respectively (Figure 1).
Although this is a cross-sectional study, there was an effect of perceived sleep quality on the association between sleep duration and depressive state. Namely, subjective sleep duration was negatively related to depressive state evaluated by PHQ-9 in subjects who failed refreshment by sleep. In subjects with refreshment by sleep, there was no change in score of PHQ-9 stratified by sleep duration.