Time trend in incidence of malignant neoplasms of the central nervous system in relation to mobile phone use among young people in Japan
Sato, Y., Kiyohara, K., Kojimahara, N. and Yamaguchi, N. (2016), Time trend in incidence of malignant neoplasms of the central nervous system in relation to mobile phone use among young people in Japan. Bioelectromagnetics. doi: 10.1002/bem.21982.
Abstract
The aim of this study was to examine whether incidence of malignant neoplasms of the central nervous system from 1993 to 2010 has increased among young people in Japan, and whether the increase could be explained by increase in mobile phone use. Joinpoint regression analysis of incidence data was performed. Subsequently, the expected incidence rate was calculated assuming that the relative risk was 1.4 for those who used mobile phones more than 1640 h cumulatively. Annual percent change was 3.9% (95% confidence interval [CI], 1.6–6.3) for men in their 20s from 1993 to 2010, 12.3% (95% CI, 3.3–22.1) for women in their 20s from 2002 to 2010, 2.7% (95% CI, 1.3–4.1) for men in their 30s from 1993 to 2010, and 3.0% (95% CI, 1.4–4.7) for women in their 30s from 1993 to 2010. Change in incidence rates from 1993 to 2010 was 0.92 per 100,000 people for men in their 20s, 0.83 for women in their 20s, 0.89 for men in their 30s, and 0.74 for women in their 30s. Change in expected incidence rates from 1993 to 2010 was 0.08 per 100,000 people for men in their 20s, 0.03 for women in their 20s, 0.15 for men in their 30s, and 0.05 for women in their 30s. Patterns in sex-, age-, and period-specific incidence increases are inconsistent with sex-, age-, and period-specific prevalence trends, suggesting the overall incidence increase cannot be explained by heavy mobile phone use.
Excerpts
A compact-sized mobile phone (about 250 g) was first introduced around 1990, followed by the start of digital mobile phone service in 1993. After a major price cut on initial costs and usage fees in 1994, mobile phone use began to spread throughout Japan. The number of mobile phone subscribers in Japan was 8 million in 1996, 54 million in 2000, 90 million in 2005, 115 million in 2010, and 137 million at the end of January 2014, with one or more phones per capita [Telecommunications Carriers Association Japan, 2014].
We extracted data on mobile phone usage from a cohort that we established using a nationwide Internet survey for mobile phone use …. Number of participants in this cohort was 7,550. In the present study, we used sex, date of birth, year starting mobile phone use, average number of calls per day, average duration of one call, and last reply date from this cohort.
In the present study, we assumed that relative risk of malignant neoplasms of the central nervous system was 1.4 for those who used mobile phones more than 1640 h cumulatively.
Annual percent change (APC) during the period from 1993 to 2010 did not show any significant increase or decrease among those aged 10–19 years: 1.6% (95% CI, −0.3 to 3.4) for men and 1.8% (95% CI, −0.4 to 4.0) for women. The APC for men aged 20 to 29 years showed a significant increase during the period from 1993 to 2010: 3.9% (95% CI, 1.6–6.3). For women aged 20 to 29 years, however, APC showed an increasing trend from 1993 to 1997, and a decreasing trend from 1997 to 2002, but neither trend was statistically significant. The APC for this group of women then showed a significant increasing trend from 2002 to 2010: 12.3% (95% CI, 3.3–22.1). The APC for those aged 30 to 39 years showed a statistically significant increase: 2.7% (95% CI, 1.3–4.1) for men, and 3.0% (95% CI, 1.4–4.7) for women. The incidence rate and best-fitting joinpoint regression model are shown in Figure 1. The observed incidence rate per 100,000 people in 1993 was 1.22 for men in their 20s, 0.53 for women in their 20s, 1.76 for men in their 30s, and 1.15 for women in their 30s. The estimated incidence rate per 100,000 people in 1993 was 1.00 for men in their 20s, 0.69 for women in their 20s, 1.55 for men in their 30s, and 1.12 for women in their 30s. The estimated incidence rate per 100,000 people in 2010 was 1.92 for men in their 20s, 1.52 for women in their 20s, 2.44 for men in their 30s, and 1.86 for women in their 30s. The change in incidence rates from 1993 to 2010 was 0.92 per 100,000 people for men in their 20s, 0.83 for women in their 20s, 0.89 for men in their 30s, and 0.74 for women in their 30s.
For men in their 20s, the proportion of heavy users started increasing from 1994, and reached 21.0% in 2010 (n = 75). For women in their 20s, the proportion of heavy users started increasing from 1996, and reached 12.0% in 2010 (n = 97). For men in their 30s, the proportion of heavy users started increasing from 1990, and reached 24.8% in 2010 (n = 234). For women in their 30s, the proportion of heavy users started increasing from 1999, and reached 12.3% in 2010 (n = 275).
The expected incidence rate per 100,000 people with the relative risk of 1.4 in 2010 was 1.08 for men in their 20s, 0.72 for women in their 20s, 1.70 for men in their 30s, and 1.17 for women in their 30s. The change in expected incidence rates with the relative risk of 1.4 from 1993 to 2010 was 0.08 per 100,000 people for men in their 20s, 0.03 for women in their 20s, 0.15 for men in their 30s, and 0.05 for women in their 30s.
In our study, the incidence of malignant neoplasms of the central nervous system for 18 years from 1993 to 2010 was found to have significantly increased in both men and women in their 20s and 30s. On the other hand, the incidence rate did not show any significantly increasing trend in men and women aged 10–19 years. If this increase in incidence was caused by a certain exposure, the effect of exposure on the incidence rate should also have increased in the last 20 years among young people aged 20–39 years, especially in men. In light of an increased risk being reported for mobile phone users with cumulative call time exceeding 1640 h, this study attempted to examine whether the observed increase in the incidence rate of malignant neoplasms of the central nervous system could be explained by an increase in the proportion of heavy mobile phone users.
Proportion of heavy users was found to be consistently higher in men than women (Fig. 2b and c), and so was the incidence of malignant neoplasms of the central nervous system, with the exception of the years 1996–1997 among women who were 20–29 years old (Fig. 1b and c). Proportion of heavy users was found to be higher among men aged 30–39 years as compared to men aged 20–29 years (Fig. 2b and c), and so was the incidence rate (Fig. 1b and c). For women, the proportion of heavy users was higher since 2006 for those aged 30–39 years compared to those aged 20–29 years (Fig. 2b and c), and the incidence rate was higher for those aged 30–39 years compared to those aged 20–29 years, with an exception in 2007 (Fig. 1b and c).
The increase in incidence rate started in 1993 for both men and women in their 20s and 30s. The incidence of malignant neoplasms of the central nervous system precedes heavy mobile phone use with the cumulative call time exceeding 1640 h. This trend was remarkable in women in their 30s. The present study does not take into account the latency period between mobile phone use and the incidence of malignant neoplasms of the central nervous system. If we assume that there is a latency period of 5 years, the incidence of malignant neoplasms of the central nervous system preceded by heavy mobile phone use is more significant.
Three major limitations of this study should be mentioned with regard to the analyzed data. First, national estimates of incidence rate, on which the present study relied, are based on regional cancer registries because a nationwide population-based registration system has yet to be established in Japan.
Second, mobile phone usage was obtained from a cohort that was created on the Internet by sending a survey to schools throughout Japan. Therefore, mobile phone usage in the cohort is considered to differ from that in the general population.
Third, the cumulative call time used in this study was calculated from the average talk time and the use period. Change in talk time over the entire period was not investigated. Cumulative call time in the present study shows a rough trend and does not reflect real usage accurately. This is another drawback of the present study.
The incidence rate of malignant neoplasms of the central nervous system has increased significantly in men and women aged 20–29 years and 30–39 years from 1993 to 2010 in Japan. However, patterns in sex-, age-, and period-specific incidence increases are inconsistent with sex-, age-, and period-specific prevalence trends, suggesting the overall incidence increase cannot be explained by heavy mobile phone use. Further epidemiological research is warranted, especially a study with a more accurate estimate of the cumulative exposure level.
--
No comments:
Post a Comment