Yoo Jin Seo

SCORES ON MORNINGNESS-EVENINGNESS AND SLEEP HABITS OF KOREAN STUDENTS, JAPANESE STUDENTS, AND JAPANESE WORKERS

The Morningness-Eveningness Questionnaire and Life Habits Inventory were given to three groups of the same mean age: 533 Korean students, 468 Japanese students, and 311 Japanese workers. The distributions of scores on the questionnaire for these three groups are normal; however the Japanese students distribution was slightly skewed towards the Evening type. The self-reported waking times and bedtimes for the three groups were late in the order of Morning, Intermediate, and Evening types. It is noteworthy, however, that the Korean students woke earlier than the Japanese students, and the workers always went to bed and woke earlier than the students. For the groups the variations in bedtime, waking time, and length of sleep were large, the sleep latency was long, and mood of the participants upon waking was bad in the order of the Morning, Intermediate, and Evening types. The scores of the Korean students were distributed more highly in the Morning type than were the Japanese students, but the students sleep habits in both countries were quite similar. The subjects categorized as Evening types had more irregular sleep habits than those of the Morning type. In comparison with the student groups, Japanese workers of the same mean age had higher scores and slightly different sleep habits. The change in sleep habits could be seen as a result of the demands of employment, and the probable basis for difference in scores.

Longitudinal study for sleep–wake behaviours of mothers from pre‐partum to post‐partum using actigraph and sleep logs

Abstract To understand the sleep–wake behaviours from the fifth pre‐partum week to the 15th post‐partum week by the number of actigraphic activities and sleep logs were evaluated in 10 women. It was found that total sleep time shortened, sleep efficiency decreased, and wake after sleep onset (WASO) increased in the weeks immediately after delivery. Compared with late pregnancy, total sleep time and sleep efficiency deteriorated significantly from the delivery week to the 12th post‐partum week and there was a longer period of WASO until the 11th postpartum week. The after‐delivery sleep parameters estimated by the actigraph were worse than those estimated from sleep logs.

Sleep in Relation to Age, Sex, and Chronotype in Japanese Workers

The Morningness-Eveningness Questionnaire and Life Habits Inventory were administered to 622 Japanese workers matched for sex and age. We investigated the distributions of the scores on the Morningness-Eveningness Questionnaire and sleep-wake habits by age and sex. Subjects were classified into five age groups and three chronotypes. The distributions and mean scores on the questionnaire advanced slightly toward the Morning type from the young to the aged group. The habitual bedtimes and waking times were significantly earlier in all the chronotypes from the young to the aged group, and the preferred bedtimes and waking times were also clearly earlier from the young to the aged group. The length of sleep was shorter for the Evening than the Morning types, especially in the group below 24 yr. The differences in habitual and preferred sleep length were greater than 1 hour for all age groups, especially the two groups under 34 yr. The number of awakenings during night sleep increased from the young to the aged group for all chronotypes. The older Evening type tended mote toward frequent napping and longer naptime. The variabilities of bedtime and sleep length were larger for the young and Evening type than for the old group and Morning types. Further, the mood upon waking and satisfaction with sleep length were better in the aged Evening type than the young Morning type. The women under 44 yr. woke up earlier than the men of the same age, and the women of the 35–54 yr. groups had a shorter length of sleep than others. These may be related to childcare and housework. These results indicated that the phase of circadian rhythms had moved forward from the young to the aged group, and the individuals rhythm, of those that were aged Morning types, showed better agreement with sleep-wake rhythms than did others.

CHANGES OF SLEEP OR WAKING HABITS BY AGE AND SEX IN JAPANESE

We analyzed the effects of age and sex on habitual sleep/wake rhythm and Morningness–Eveningness scores of 2,252 subjects (6–89 years) randomly selected in Shimonoseki, Japan. Subjects were divided into 21 age groups with a matching number of men and women in each age group. The most common sleep parameter patterns by age showed a v- or ^-pattern with a turning point in young adulthood or at the period of puberty. During the period between 6 yr. of age to puberty or young adulthood, the bedtimes on weekdays and weekends and the waking times on weekends were delayed, Morningness–Eveningness scores shifted to the evening type, and sleep length on weekdays decreased. After that period, across groups of increasing age, bedtime and waking time on weekdays and weekends became earlier, sleep length on weekdays and sleep latency increased, Morningness–Eveningness scores shifted to morning type, and the number of awakenings increased. The number of daytime naps increased in the 16–19 yr. group, decreased slightly after that age group, but increased again in older groups. The weekday bedtimes of women above 40 yr. of age was significantly later and their sleep lengths significantly shorter than those of men of the same age. Average sleep latency was longer for women than men. The number of awakenings was larger in women above 50 yr. of age than men of the same age group. The turning point of age gained from the two linear regressions on data for subjects that have a minimum sum of squared error, was between 16 and 25 yr. of age. Average phase of sleep/wake rhythm shifted backward and sleep length decreased in groups from age 6 to puberty or young adulthood. After early adolescence, the average phase of the sleep/wake rhythm shifted forward, sleep latency became longer, and daytime napping increased. Number of awakenings increased rapidly for womens groups over 40 yr. of age and for mens groups after 50 yr. of age. Sex differences in our research are in apparent conflict with previous data and are discussed from the perspective of womens social and domestic roles in Japan.

SLEEP AND CHRONOTYPE FOR CHILDREN IN JAPAN

To investigate the change in sleep-wake habits, Morningness-Eveningness preference, and sleep status by grade, 512 students aged from 6 to 18 years, were tested using the Morningness-Eveningness Questionnaire and Sleep Questionnaire. The habitual waking time showed no difference by grade, but the students above Grade 7 reported a significantly later habitual bedtime and had a shorter length of sleep on weekdays than the students below Grade 6. The students above Grade 7 reported a significant difference between habitual and preferred waking times but did not show a difference between habitual and preferred bedtimes. Although the sleep length during weekends became shorter from Grade 1, the sleep length of students above Grade 8 showed a significant difference between the weekdays and weekends; they had more than nine hours of sleep on the weekends. The percentage of students taking a nap during a school lesson significantly increased across Grades 8 to 12. The mean score on the questionnaire decreased across grades and the decrease was significant at Grade 7. Both the habitual and preferred bedtimes and waking times were later from the Morning, Intermediate, to the Evening types across grades. The difference by chronotype in preferred waking time increased for groups from the primary, junior high, to the high school. Also, the sleep lengths both weekdays and weekends decreased from the Morning, Intermediate, to the Evening type for all grades. We suggested that the delay of sleep phase, reduction of sleep length, increased daytime napping, and transition to Evening type were remarkably represented around Grade 7.

Age and gender difference in habitual sleep–wake rhythm

We analysed the effects of age and gender on the habitual sleep–wake rhythm in 2252 randomly selected subjects living in Shimonoseki, Japan. Subjects were divided into 21 age groups with a matching number of males and females for each. During the period from primary school to adolescence, the bedtime became delayed and sleep length decreased with age. After that period, with increasing age, bedtime became earlier and sleep length increased. The number of awakenings and the length of daytime naps increased markedly with epoch after 50 years and 70 years of age, respectively. Gender differences were considered to be due to the women’s social and domestic customs in Japan.

Effects of Age and Gender on Sleep Habits and Sleep Trouble for Aged People

The healthy 455 subjects above 60 years of age were questioned on their sleep habit inventory and the morningness-eveningness questionnaire. We analyzed the effects of age and sex on sleep habits and sleep-related trouble. Bedtimes on weekdays and weekends became earlier with aging, and women went to bed significantly later than men did. The length of sleep on weekdays slightly increased with aging, and it was longer for men than for women. The number of urinations and awakenings during nocturnal sleep and the amount of daytime napping increased with aging. The score on morningness-eveningness shifted toward the morning type with aging. In comparison with men, women had significantly longer sleep latency; and a higher percentage of subjects who reported that they sleep for only a short time, have sleep trouble, have received medical treatment for their sleep trouble, and take sleep medication. From these results, we deduced that the phase of sleep shifted forward in subjects above 60 years of age, and they showed frequent interruptions during nocturnal sleep and long daytime napping. We discussed the factor of gender difference in sleep in relation to social and cultural factors, particularly the household activities of women.

Changes in sleep patterns during simulated nitrox saturation diving to 20 and 30 meters.

This study assessed the effect of a nitrogen-oxygen (N2-O2) saturation diving environment on nocturnal sleep and the differences in sleep on diving depth. We measured and recorded the standard polysomnograph and heart rate for a total of 459 nights on 27 divers who performed the N2-O2 saturation simulation dive at 20- and 30-m equivalent depths as well as their subjective feelings of fatigue. From the last half of the period on the bottom to the postdive period of both saturation diving depths, our main findings included a prolongation of sleep latency, shortened total sleep time, a decreased sleep efficiency index, and increased feelings of fatigue. During the bottom period and decompression period, the total number of awakenings and the awakenings from rapid eyes movement (REM) sleep increased. This was slightly greater at the 30-m equivalent depth. From these facts, we assumed that the deterioration of sleep at the 20- and 30-m nitrox saturation dives was predominantly relative to being restricted in a closed environment for a long time and the lack of physical activity of the divers. No recovery of sleep was observed in the postdive period. A difference in the effects on sleep by the dive depth was not found.