It is estimated that as of 2011, globally, the number of cell phone subscribers are more than 5.5 billion and more than 350 million subscribers to cell phone in the United States; nearly threefold increase from the year 2000. Over a period, the number of cell phone calls per day, the length of each call and the amount of time people spending on cell phones, have increased. Cell phone technology has also undergone substantial changes.
Working of cell phones and radiation absorption
Cell phones communicate with nearby cell towers through RF waves, a form of energy spectrum between FM radio waves and microwaves. Like FM radio waves, microwaves, visible light, and heat, they are a form of non-ionizing radiation.
Part of the radio waves emitted by a mobile telephone handsets are absorbed by the human head. The radio waves emitted by a GSM handset can have a peak power of 2 watts, and a US analogue phone had a maximum transmit power of 3.6 watts. Other digital mobile technologies, such as CDMA2000 and D-AMPS, use lower output power, typically below 1 watt.
The rate at which radiation is absorbed by the human body is measured by the Specific Absorption Rate (SAR), and its maximum levels for modern handsets have been set by governmental regulating agencies in many countries. In the USA, the FCC has set a SAR limit of 1.6 W/kg, averaged over a volume of 1 gram of tissue, for the head. In Europe, the limit is 2 W/kg, averaged over a volume of 10 grams of tissue.
Effects of radiation
Although many studies have examined the potential health effects of non-ionizing radiation from radar, microwave ovens, and other sources, there is currently no consistent evidence that non-ionizing radiation increases cancer risk.
The only known biological effect of radio frequency energy is heating. The ability of microwave ovens to heat food is one example of this effect of radiofrequency energy. Radiofrequency exposure from cell phone use does cause heating; however, it is not sufficient to increase body temperature significantly.
Recent study of link between cell phone use...
and brain cancer / central nervous system tumors
Researchers from the Institute of Cancer Epidemiology at the Danish Cancer Society in Copenhagen looked at national health and mobile phone records in Denmark, and compared cancer rates between long-term mobile phone users and the rest. They published their findings in the 20 October issue of the British Medical Journal (BMJ ).
The researchers collected health data record of all aged 30 and over who were born in Denmark after 1925, and the divided this population into two groups: those who became mobile phone subscribers before 1995. This came to about 3.6 million subscribers and the rest about 3.2 million.
They then cross-referenced this data with entries in the complete Danish Cancer Register to calculate the risk of tumors of the central nervous system.
They concluded “There was no indication of dose-response relation either by years since first subscription for a mobile phone or by anatomical location of the tumor – that is, in regions of the brain closest to where the handset is usually held to the head. In this update of a large nationwide cohort study of mobile phone use, there were no increased risks of tumours of the central nervous system, providing little evidence for a causal association.”
Hazel Nunn, head of evidence and health information at Cancer Research UK, said that this study was the “strongest evidence yet”, and “minimized many of the problems of previous research in this area. However she urges for continued monitoring.