Transport and Chronic Injuries of Cell Phone use on Human Health: A Systematic Analysis of Epidemiological Evidence

Background Cell phone use brought convenience to people, but using phones for a long period of time or in the wrong way and with a wrong posture might cause damage to the human body. This study was designed to assess the impact of cell phone use on transport and chronic injuries. Methods Studies were systematically searched in four database and relevant reviews were searched to identify additional studies. A total of 41 studies met the inclusion criteria. Results Cell phone users were at a higher risk for transport injuries (RR: 1.37, 95%CI: 1.22−1.55), long-term use of cell phones increased the transport injury risk to non-use or short-term use (RR: 2.10, 95% CI: 1.63−2.70). Neoplasm risk caused by cell phone use was 1.07 times that of non-use (95% CI: 1.01−1.14); Compared with non-use, cell phone use had a higher risk of eye disease, with a risk of 2.03 (95% CI: 1.27−3.23), the risk of mental disease was 1.26 (95% CI: 1.17−1.35), the risk of neurological disorder was 1.16 (95% CI: 1.02−1.32), and a pooled risk of other chronic injuries, was 1.20 (95% CI: 0.98−1.59). Subgroup analyses found that motor crashes had significantly increased (OR: 1.25; 95%CI: 1.18−1.32), as well as the risk for hearing problems (OR: 4.54; 95%CI: 3.29−5.80), headaches (OR: 1.25; 95%CI: 1.18−1.32), and abnormal biochemical indicators (OR: 0.51; 95%CI: 0.04−0.99). reasonably.

such as hear loss, visual impairment, cervical injury, and internet addiction. Currently, people pay attention to injuries caused by cell phone use. Although most of the studies focused on a specific type of injury, such as tumors, headaches, and mental health 13-18 , there are types of injuries that have not been reviewed yet and of which more evidence needs to be summarized. Given that the use of cell phones was growing rapidly, our study will provide a thorough review of the impact of cell phone use on the human body health, including transport injuries and chronic injuries.

Search strategy
Two of the authors (XC and CX) systematically searched the databases PubMed, EMBASE, Cochrane, and Web of Science up to April 4, 2019. The search was limited to human body studies published in the English language. In addition, additional literature was screened by manually searching for the reference lists of recent reviews and included studies. The two authors (XC and CX) worked simultaneously, but independently screened the studies with the inclusion criteria and the extracted data, and assessed the study's quality. The results were crosschecked by each other, and any disagreement on study selection, data extraction, and study quality assessment was resolved by a third author (YH).

Inclusion And Exclusion Criteria
Transport injuries were mainly road injuries (car accidents, motorcycle accidents, or motor crashes). Chronic injuries included neoplasm disease(brain tumor, thyroid cancer, glioma and astrocytoma), mental disease (Attention Deficit Hyperactivity Disorder [ADHD], Nomophobia-anxiety, insecurity, anger, discomfort), neurological disorder (headaches, sleep problems), sensory system disease (eye disease, hearing problem), oral health, wrist extension damage, reproductive health, and other chronic injuries (including DNA damage, genotoxic effects, blood-cerebrospinal fluid barrier [BCSFB], serum S100B levels, tPSA, fPSA, fPSA/tPSA, DNA intergrity, chromosomal damage). Our study inclusion criteria were (i) focused on damage, including transport and chronic injuries, instead of promoting healthy outcomes; (ii) using cell phones, including digital phone and cell phone radio frequency radiation); (iii) transport injuries occurring during cell phone use; chronic injuries resulting from cell phone use rather than any other cause (e.g., occupational injuries); (ⅳ) published in English; and (ⅴ) outcome indicators including Odd Ratios/ Relative Risks (OR/RR) and their 95% confidence intervals (CIs) or the mean with their standard deviation (Mean ± Standard Deviation, M ± SD).
Abstracts, comments, conferences, replies, responses, reviews (including systematic reviews), case reports, and animal studies were excluded from the present analysis. Additionally, studies with incomplete data or duplicate publications were also excluded.

Data Extraction And Quality Assessment
Two reviewers (XC and CX) independently conducted data extraction and assessed the study's quality according to the predefined inclusion criteria. The following information was collected using standardized data extraction forms: author information, publication year, study design, participant age, sample size, study area, measures of cell phone use, measures of outcome-related behavior, and key outcomes. All data were double-checked.
The Newcastle−Ottawa Scale (NOS) was designed for the evaluation of case-control studies and cohort studies. The evaluation criteria for cross-sectional studies included 11 items recommended by the Agency for Healthcare Research and Quality (AHRQ). The quality of each study was graded as good, fair, or poor. To be rated as good, studies needed to meet all criteria. A study was rated as poor when one (or more) domain was assessed as having a serious flaw. Studies that met some but not all criteria were rated as fair. Any disagreements or discrepancies regarding study selection, data extraction, and quality assessment were resolved by consensus.

Data Analysis
A random-effects model was used to estimate the overall pooled estimates. Tests for heterogeneity between the study results were performed with the Cochran's Q statistic and quantified with the I 2 statistic.
To examine the robustness of the findings, we performed subgroup analyses by study country, participant age, sample size, and study-specific outcomes (transport and chronic injury). To validate the robustness of the findings, we performed a sensitivity analysis. The potential for publication bias was graphically explored through the production of funnel plots and tested for significance with Egger's test and Begg's test. All statistical procedures used a two-sided significance level of 0.05 and were conducted with Stata version 13.0.

Results
A detailed flowchart of the literature searching process and study identification is presented in Fig. 1. First, 4,225 studies were identified by the initial database search, and three articles were obtained by searching references; 2,324 articles were still included after the removal of duplicates. After screening the titles and abstracts, 1,922 records were excluded because they did not meet the selection criteria [e.g., case reports (n = 9), summary reviews (n = 117), animal studies (n = 255), not about cell phone use (n = 1257), non-English (n = 2), replies/abstracts (n = 23), and no outcome indicators (n = 259)]. Then the full text articles were assessed for eligibility; 142 records were excluded because they were duplicates (n = 2), a case report (n = 1), summary reviews (n = 9), non-crowed research (n = 29), not about cell phone use (n = 10), not in English (n = 3), a reply (n = 1), or lacked outcome indicators (n = 87). Finally, 41 studies 12−53 were included, including cohort studies (n = 10), case−control studies (n = 20), and cross-sectional studies (n = 11). The details of the search strategy are presented in the Appendix (Table S1).
The characteristics of the included articles are presented in Table S2. Twenty-eight studies were published between 2011 and 2019, 12 were published between 2001 and 2010, and 1 was published in 1997. The sample sizes of the included studies ranged from 6 to 15, there were 406,515 participants in total, and all participants were over 7 years old. Of the included studies, 8 studies were carried out in the United States, 5 in Sweden, 3 in Canada, 3 in Korea, 2 in China, 2 in Vietnam, 2 in Iran, 1 in Denmark, 1 in Italy, 1 in Malaysia, and 1 in Brazil. The remaining studies lacked relevant regional information. Outcomes were divided into transport and chronic injuries. Fifteen studies focused on transport injuries, which were mainly related to road injuries and unintentional injuries, such as electrical injuries and explosions. Twenty-six studies focused on chronic injuries, such as tumors, ocular health, oral diseases, DNA damage, joint injuries, hearing damage, and male reproductive health conditions.
The results of the quality assessment indicated that 16 studies were of good quality, and 25 were rated as fair (Table S3).
[The non-neoplasm injuries included eye disease, mental health (ADHD), neurological disorder [headaches, sleep problems], and other chronic injuries (including BCSFB, Serum S100B levels).] [Chronic injuries included hearing problem, mental health [ADHD, Nomophobia-anxiety, insecurity, anger, discomfort], oral health, and other chronic injuries [including tPSA, fPSA, fPSA/tPSA, DNA integrity, chromosomal damage, DNA breaks, genotoxic effects] Subgroup analyses showed a consistent increase in the overall risk of cancer in the dialysis population (Table 1) Publication biases may exist when the publication status depends on the statistical significance of the study results. We conducted a funnel plot analysis to check for a potential publication bias; the funnel plot was generally symmetric, indicating the absence of a publication bias ( Figure S1). Table 1 Subgroup analyses of the risk of injuries with cell phone use.

Discussion
Our study included large participant-level cohort, cross-sectional and case−control studies on the impact of cell phone use on human body outcomes. The findings suggested that cell phone use increased the risk of transport and chronic injuries involving the human body. The risk of transport injuries due to cell phone use was 1.55 times higher than when not using cell phones, and car accidents and motor crashes were the highest relative risks of traffic injuries;Cell phone use also increased the risk of chronic injuries.
Consistent with the findings of previous studies 55-58 , cell phone use was more prone to transport injuries. Phone use while driving has become one of the priority issues in road safety, given that it may lead to decreased situation awareness and deteriorated driving performance. Although it is difficult to assess the absolute increased risk for collision due to distraction of the driver caused by using cell phones, existing studies have shown that the risk of talking on the phone while driving is significantly higher than that of undistracted driving and is comparable to the risk of drunk driving 55 . Texting or typing is more likely to increase the risk of traffic than other types of observable distraction, and previous risk studies have shown that such visual manual tasks greatly increase the risk of a crash 59, 60 . Ludovic 61 et al. found that cell phone use while driving was a significant distraction, especially in young drivers, thus becoming a leading cause of motor vehicle crashes. For example, drivers were more likely to miss traffic signals and were involved twice as often in car crashes when having a phone conversation while driving. A study conducted by the Florida State University found that even when a user is not using a cell phone, the vibration or beeping of the phone will attract the user's attention, which may severely impact the driving. Alghnam 62 investigated the association between cell phone use and distracted driving through a case−control method and found that using cell phones while driving would increase the risk of road traffic injuries.
Some interventional driving strategies and preventive measures have reduced the risk of traffic accidents among people, such as the graduated driver licensing program and advertising campaigns. So far, few therapeutic approaches have been implemented. For example, United States, Great Britain, Canada, South Africa, and Australia had developed and used "The Graduated Driver Licensing" (GDL) program, which allowed drivers to gain experience in low-risk driving conditions by adding an "intermediate" phase between the learning stage and the acquistion of the driving license 63 . While many studies showed that the effectiveness of educational and preventive road safety programs is yet to be confirmed 64 .
In addition, previous studies found that excessive use of cell phones can cause chronic injuries. Cell phone radiation has been classified as possibly carcinogenic to humans. Previous evidence of damage from RF-EMF is the strongest for cancer caused by long-term exposure to cell phones, and especially brain tumor gliomas 65 , glioblastomas 66 , and acoustic neuromas. In fact, the rates of brain tumors are increasing in Sweden, and the use of wireless phones has been suggested to be the cause 67 . There appears to be sufficient evidence that RF-EMF, although not causing tissue heating, can cause non-thermal biological effects. Deniz 68 evaluated the effects of phones on the human brain using stereological and spectroscopic methods and neurocognitive tests, and found that a lack of attention and concentration may occur in subjects who talk on the phone for a longer amount of time, unlike those who use phones relatively less. Some studies have shown that cell phone use can also cause wrist damage, such as cervical vertebra injuries and wrist joint injuries 69 . Fei 70 and Kim 71 found that cell phone use that was not conducive to the proper spinal posture increased the risk of chronic neck and shoulder pain, and pain and fatigue worsened with longer cell phone use. People are in a relaxed state while using their cell phones, especially the neck, which is in a bent state. It was shown that there was a positive correlation between neck flexion and neck force, as well as head and neck posture in the cervical spine stress and related neck pain 72 . Besides, long-term use of cell phones was harmful to the mental health, and caused headaches and sleep disorders 73,74 . They also found that using cell phones before bedtime could cause sleep disorders and could lead to a rapid decline in cognitive and learning abilities among students. Cell phones are playing an increasingly important role in our lives; people have become dependent on cell phones and suffer from "no mobile phone phobia" (i.e., when not having a cell phone, individuals feel discomfort, insecurity, Alzheimer's disease is increasing in many countries, and its association with ELF-EMF occupational exposure has been clearly demonstrated through several independent epidemiological studies. A prospective epidemiological study 87 has shown that Alzheimer's disease is significantly associated with chronic ELF-EMF occupational exposure. In addition, at greater EMF strengths or shorter exposures, the ability of the body to develop compensation mechanisms is reduced, and the potential for heart-related effects increases. This suggests that the presently allowed radiation emission levels for cell phones, although low, might be sufficient to induce biological effects. However, determination of whether these effects might cause any significant health effects requires further investigation. Inskip et al 88-90 also reported that the existing data are not sufficient to support the assumption that tumors were caused by cell phone usage.
Our study also has some limitations. First, "damage" and "injury" were used as search queries in our study to retrieve reports on the health effects of cell phones. Other adverse outcomes caused by phones may have been missed, and we expect to include more outcomes in future studies. Second, the small sample sizes of several studies could limit the reliability of their statistical results in specific categories and increase the likelihood of chance differences. More empirical evidence is needed to have more reliable estimations of cell phone use and its impact on human health, especially concerning chronic injuries. Third, only 10 of the 41 included studies were longitudinal studies, we lacked more longitudinal studies to confirm the causal relationship between cell phone use, and human transport and chronic injuries. Fourthly, the different environments and behaviors of using mobile phones might lead to different injury risks, we did not consider different patterns or reasons for using mobile phones in different regions and by different people, nor did we further analyze the specific types and purposes of using mobile phones, such as texting or making phone calls. Finally, there was a significant heterogeneity in our study, and we did a subgroup analysis to explore the source of heterogeneity. However, the results of this subgroup analysis did not fully explain such heterogeneity, and we need to conduct further studies to explore this.

Conclusions
There is growing evidence that cell phone use impacts the human body. Our study suggests that the use of cell phones causes not only transport injuries, but also chronic injuries to the human body. Although some findings are still controversial, the harm that cell phones have caused to the human body cannot be underestimated, and more research is needed to explore the direct evidence of damage to the human body. Therefore, it is necessary for cell phone users to reduce the cell phone usage time, maintain a correct posture when using cell phones, and take appropriate protective measures, such as anti-blue light glasses. As for the manufacturers, they need to improve their technology to cause less radiation and light damage to the human body. Cell phone use is ubiquitous and facilitates people's daily lives. It is essential to increase the awareness of correct and reasonable use of cell phones to reduce the injuries caused by cell phone use.

Ethics approval and consent to participate
Not applicable.

Consent for publication
Not applicable.

Availability of data and materials
All data generated and analysed during this study are included in this published article [and its supplementary information files, Table S2].

Figure 1
Flowchart of the selection of articles. Flowchart of the selection of articles.

Figure 2
Forest of transport injury risk and cell phone use.  Forest of chronic injury risk (neoplasm injury) and cell phone use.

Figure 3
Forest of chronic injury risk (neoplasm injury) and cell phone use. Forest of chronic injury risk (non-neoplasm injury) and cell phone use. Forest of chronic injury risk (non-neoplasm injury) and cell phone use.

Figure 5
Forest of chronic injury risk and cell phone use (continuous data).

Figure 5
Forest of chronic injury risk and cell phone use (continuous data).

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