Electronic devices with visual displays are now being used by people all over the world. Among such devices, smartphones have become universally available due to their compact nature. In Japan, the household ownership rate for smartphones increased from 49.5% in 2012 to 75.1% in 2017 , and the individual ownership rates for smartphone in 2017 were 94.5% for people in their 20’s and 79.5% for people of 13 to 19 years of age .
Smartphones use for a long period of time can cause visual display terminal (VDT) syndrome. It has been reported that smartphones use was strongly associated with dry eye disease in children  and that smartphones use can aggravate asthenopia and induce tear film instability and oxidative stress in the tears and at the ocular surface . Studies have shown that VDT users might be at increased risk of developing musculoskeletal symptoms   and mental and physical health problems . Recent studies have shown that smartphones operation with one hand caused greater upper trapezius pain  and overuse of smartphones are associated with anxiety in students  . It has been reported that performing an exciting VDT task with a bright display suppressed nocturnal changes in melatonin level and physiological indicators of the human biological clock . It has also reported that the use of light-emitting electronic devices for reading before bedtime prolonged the time it takes to fall asleep, delayed the circadian clock, and reduced melatonin levels . Circadian rhythm disorders can cause not only sleep disturbance but also hypertension, diabetes mellitus and obesity  . Recently, it was found that blue-enriched light exposure acutely alters glucose metabolism and sleepiness .
On the other hand, menstruation-related symptoms such as premenstrual symptoms and menstrual pain are now focusing on the diseases to influence to their quality of health for young female generation. Premenstrual symptoms are that various physical and psychological uncomfortable symptoms occur in women before menstruation, and their pathological state is called premenstrual syndrome (PMS). It has been reported that secretion of melatonin in the luteal phase was less than that in the follicular phase in women with PMS , and healthy women are likely to have insomnia due to a decrease in melatonin secretion before menstruation . Disturbance of circadian rhythm by using electronic devices may affect menstruation-related symptoms including premenstrual symptoms and menstrual pain in young women, but this association has not been clarified.
The purpose of this study was to clarify the differences in physical and psychological condition, sleeping status and menstruation-related symptoms before and after starting to use smartphones in female university students in Japan.
2. Materials and Methods
We conducted this cross-sectional survey between June and November in 2016. We recruited 273 female nursing students at a university in Japan. The students were asked to complete a questionnaire at the end of a lecture, and the questionnaires were collected on the same day. Informed consent was obtained prior to participation in the study. This study was approved by the Ethics Committee of Tokushima University Hospital (approval number: 2595).
We designed a self-administered questionnaire (appendix) that took about 15 minutes to complete. The first part of the questionnaire consisted of questions on age, body height and weight, and menstrual status including age of menarche, menstrual regularity, menstrual amount and duration, menstrual cycle and presence of dysmenorrhea. The second part consisted of questions on 1) age when starting to use smartphones and number of hours used each day, 2) differences in physical conditions (appetite, body weight, constipation, eyestrain, eyesight, posture, stiffness, dryness of eyes, dizziness, ringing in the ears, nausea and headache and activity such as increase in time spent sitting or lying after starting to use smartphones, degrees of deterioration in eyesight and decline in physical strength) before and after starting to use smartphones, 3) differences in psychological conditions (irritability, difficulty concentrating, lack of motivation, sensitivity to stress) before and after starting to use smartphones, 4) differences in sleeping status before and after starting to use smartphones, 5) differences in menstrual status and menstruation-related symptoms such as premenstrual symptoms (irritability, depression, emotional instability, difficulty concentrating, breast tenderness, fatigue, rough skin, hypersomnia and increase in body weight), and menstrual pain (abdominal pain, headache and low back pain) before and after starting to use smartphones and 6) strategies for coping with various symptoms (decreasing the duration of use, frequent breaks, applying eye lotion, using protective eyeglasses, using in a place with sufficient brightness, not using before sleeping, visiting hospitals, taking medications, doing eye massages or eye exercises, looking far away, viewing the screen from a distance and using with eyes closed).
2.2. Statistical Analysis
Each categorized variable is expressed as a number with percentage. The significance of differences in physical and psychological conditions, sleeping status, and menstrual conditions before and after starting to use smartphones was evaluated by the chi-square test. Statistical analyses were carried out using SPSS version 20 for Windows. All p values are two-tailed and those less than 0.05 were considered statistically significant.
3.1. Background Characteristics of the Participants
The response rate for the survey was 95.2% (260/273). The mean age ± standard deviation of the students was 20.0 ± 1.9 years. The results showed that 2.4% of the students started to use smartphones in elementary school (6 - 12 years old), 12.5% in junior high school (12 - 15 years old), 63.5% in high school (15 - 18 years old) and 21.6% in university. The duration spent using smartphones were 3 - 5 hours per day for 36.5% of the students, less than 3 hours for 29.4%, 5 - 7 hours for 19.6%, 7 - 9 hours for 11.1% and more than 9 hours for 3.5%.
3.2. Differences in Physical Conditions before and after Starting to Use Smartphones
There were significant differences before and after starting to use smartphones in eyestrain, posture, stiffness of the neck, back and shoulders, and level of outdoor activity on a holiday (Table 1). Degrees of deterioration in eyesight were severe in 12.3% of the students, moderate in 33.5% and slight in 28.8%. The
Table 1. Differences in physical conditions before and after starting to use smartphones.
Number (%), ns: not significant.
proportion of students who increased time spent sitting or lying after starting to use smartphones was 48.1%. Degrees of decline in physical strength after starting to use smartphones were severe in 3.1% of the students, moderate in 16.1% and slight in 43.1%. Physicals symptoms that occurred after starting to use smartphones were dryness of eyes (59.2% of the students), dizziness (7.3%), ringing in the ears (5.0%), nausea (1.9%) and headache (26.7%).
3.3. Differences in Psychological Conditions before and after Starting to Use Smartphones
The proportions of students with difficulty concentrating, lack of motivation and sensitivity to stress were significantly higher after starting to use smartphones (Table 2).
3.4. Differences in Sleeping Status before and after Starting to Use Smartphones
There were significant differences before and after starting to use smartphones in the time spent using smartphones before sleeping, bedtime, sleeping hours,
Table 2. Differences in psychological conditions before and after starting to use smartphones.
Number (%), ns: not significant.
feeling of sufficient sleep, refreshed feeling after waking up and wake-up time on a weekday. The proportion of students who had less sleeping hours, less feeling of sufficient sleep and less refreshing feeling after waking up after starting use smartphone were higher than those before using smartphones (Table 3).
Table 3. Differences in sleeping status before and after starting to use smartphones.
Number (%), ns: not significant.
3.5. Differences in Premenstrual Symptoms before and after Starting to Use Smartphones
As shown in Table 4, regarding premenstrual symptoms, the proportion of students without fatigue decreased from 29.2% before using smartphones to 23.8% after starting to use smartphones, while the proportion who felt fatigue to some extent or severe increased from 25.8% to 33.1% and from 9.2% to 12.3%, respectively. The proportion of students with physical symptoms such as fatigue before menstruation was significantly higher after starting to use smartphones. The proportions of students with irritability and depressive feeling as emotional premenstrual symptoms showed tendencies to be higher after starting to use smartphones.
3.6. Differences in Menstrual Pain before and after Starting to Use Smartphones
The proportion of students without headache and low back pain during menstruation decreased from 35.0% before using smartphones to 30.4% after starting to use smartphones, while the proportion with pain to some extent or severe increased from 27.7% to 29.2% and 5.8% to 7.3%, respectively (Table 5). The proportion of students with headache and low back pain during menstruation were significantly higher after starting to use smartphones.
3.7. Strategies for Coping with Various Symptoms
Strategies used to cope with various symptoms caused by using smartphones were decreasing the duration of use (13.4% of the students), frequent breaks (10.2%), applying eye lotion (16.3%), using protective eyeglasses (4.3%), using in a place with sufficient brightness (12.9%), not using before sleeping (7.9%), visiting hospitals (0.4%), doing eye massages (8.6%) or eye exercises (4.1%), viewing the screen from a distance and using with eyes closed (11.3%).
In the present study, we confirmed that the proportions of students who had deterioration of ocular symptoms increased, and there were significant differences in eyestrain, posture, stiffness of the neck, back and shoulders, and level of outdoor activity on a holiday before and after starting to use smartphones. Previous studies revealed that VDT users have increased risks for ocular, musculoskeletal, and mental health problems      . For psychological symptoms, it has been reported that psychological distress was related to maladaptive use of both the Internet and mobile phones . It was shown that there is a negative association between excessive smartphones use and psychological well-being  . We found that the proportions of students with psychological conditions such as difficulty concentrating, lack of motivation and sensitivity to stress increased after starting to use smartphones.
We showed that the proportions of students with sleep disturbance increased
Table 4. Differences in premenstrual symptoms before and after starting to use smartphones.
Table 5. Differences in menstrual pain before and after starting to use smartphones.
after starting to use smartphones. It has been reported that “smartphone use after lights out” was related to sleep disorders and life rhythms , and disturbance of circadian rhythm and sleep deficiency affect various psychological functions . Moreover, disturbed sleep habituation including delayed bedtime and insufficient sleeping hours was associated with depression and irritability . The use of smartphones may cause poor psychological conditions through disturbances of circadian rhythm and sleeping.
With respect to premenstrual symptoms, we found that the proportion of students with fatigue before menstruation was higher than after starting to use smartphones and the proportion of students with irritability and depressive feeling as emotional premenstrual symptoms tended to be higher than after starting to use smartphones. It has been reported that factors such as insufficient stress coping, insufficient sleep, menstrual distress and smoking habit indirectly cause PMS . Since it has been reported that decrease in melatonin secretion in the luteal phase was found in women with PMS , premenstrual symptoms may be associated with melatonin level. Also, longer daily VDT use might result in deterioration of mental health status . Deterioration of symptoms such as delayed wake-up time on a weekday, difficulty concentrating and sensitivity to stress after using a VDT for a long time may be associated with deterioration of psychological premenstrual symptoms. In addition, deterioration of sleep disturbances and difficulty concentrating caused by smartphones use may be involved in aggravation of physical premenstrual symptoms. Attention must be given to psychological distress and sleep disturbance, particularly before menstruation, to prevent deterioration of premenstrual symptoms. It has been reported that exposure to low-intensity blue light in the evening elicits drowsiness and suppression of energy metabolism the following morning . Exposure to blue light by using smartphones may induce a decrease in metabolism in the body since an increase in body weight was found before menstruation.
We found that the proportion of students with headache and low back pain during menstruation was significantly higher than after starting to use smartphones. The etiology of primary dysmenorrhea includes an excess or imbalance in the secretion of prostaglandins (PGs) from the endometrium during menstruation. It has been reported that an increase in PGE2 metabolite levels in response to sleep loss was associated with spontaneous pain complaints . Also, there was a relationship between sleeping hours and menstrual pain  and sympathetic nerve activities were higher during the luteal phase and that fluctuation in sympathetic nerve activities was increased by exposure to white light-emitting diodes . The threshold for sensitivity to stress as well as for pain stimulation may be changed by using smartphones.
The students have done variety of strategies for coping with symptoms that occurred by using smartphones in the present study. Appropriate smartphones use and coping with VDT-related symptoms are important to reduce the occurrence of not only VDT-related symptoms but also menstruation-related symptoms. VDT devices including smartphones will be used more widely in the future. For their adverse effects, young women should avoid excessive use of them. Parents, teachers and medical staff should understand and educate children and students about the adverse effects of using smartphones. In addition, further study will be needed for identifying strategies to reduce the smartphone-related symptoms or negative health conditions in students.
There are limitations in this study. First, this study is cross-sectional survey that has recall bias and the period to start using smartphones varies by each student. Physical and psychological symptoms might vary in each menstrual cycle. The period after starting to use smartphones is rather short since smartphones have become popular only in the past few years. Thus, the effects of smartphones on physical and psychological conditions, sleeping status and menstruation-related symptoms over a long period should be investigated using a prospective study. Second, some students may have medical histories such as gynecological diseases, and it might influence to our results such as menstrual pain. Third, detail of conditions on smartphones use, which is size of screen, degree of the screen light, the purpose of use smartphone, duration of using it might influence of results. Finally, objective evaluation by using a VAS score, and determination of sleeping status by using actigraphy are needed.
In conclusion, there were significant differences in eyestrain, posture, stiffness of neck, back and shoulders, and level of outdoor activity, difficulty concentrating, lack of motivation, and sensitivity to stress, fatigue before menstruation and headache/low back pain during menstruation before and after starting to use smartphones. Young women should refrain from using smartphones if they have VDT-related symptoms, disturbance of sleep pattern and menstruation-related symptoms before and during menstruation.
The authors extend their thanks to the participants in this study.
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