Goldwein O, Aframian DJ. The influence of handheld mobile phones on human parotid gland secretion. Oral Dis. Ahead of print Sep 8, 2009.

The use of handheld mobile phones (MPH) is now widespread, raising concerns about possible adverse health effects from exposure to radiofrequency radiation (RFR) emitted by the device.  In humans, the parotid glands are the largest salivary glands, situated in front of the ear and behind the mandible, close to the skin of the face. Saliva is 99% water; the rest is comprised of bioactive molecules crucial for many tasks.  Some studies have found an association between the use of handheld mobile phones and parotid gland tumours. Nonetheless, the effects of radiofrequency radiation on parotid gland physiologic function are still unclear.

This study compared the parotid salivary secretion rate and protein concentration between dominant and less dominant sides of subjects from a healthy population who use handheld mobile phones.

The study subjects were 50 healthy volunteers (25 men, 25 women) aged 19-33 years who reported a preferred side of use of handheld mobile phone. Subjects completed a questionnaire on typical handheld mobile phone use.  Saliva secretion rate of both parotid glands was measured simultaneously between 8:00 and 12:00 am, with a total collection time of 5 minutes.

The mean time of handheld mobile phone use among study participants was 7 years.  More than half reported using handheld mobile phone at least 5 times a day and almost half used hands- free accessories. Overall, a 2.54-fold increase in salivary secretion rate was found in the dominant compared to the non-dominant side.  As the number of years of handheld mobile phone use increased, the ratio of saliva secretion between dominant and non-dominant sides decreased.  No correlation was found between daily handheld mobile phone time use and the saliva secretion rate.  The mean total protein per millilitre (ml) concentration was slightly higher in the dominant side (1.2-fold) than in the non-dominant side, but this difference was not statistically significant.  No correlation was found between the number of years of handheld mobile phone use or daily handheld mobile phone time use and protein concentration.

Interpretation and Limitations
The authors propose several potential explanations for their results.  Since chewing forces are stronger on the dominant side, and since chewing stimulates saliva secretion, higher secretion rates would be expected on the dominant side.  Salivary secretion is regulated by the autonomic parasympathetic and sympathetic nervous system, with the prior inducing more waterish saliva and the latter generating the protein secretory component.  The different effect of handheld mobile phone use on fluid vs. protein concentrations in this study may be due to the different effects of handheld mobile phone use on parasympathetic and sympathetic pathways, an effect observed in another study. The heat produced by handheld mobile phones results in a slight increase in skin temperature adjacent to the phone. The authors hypothesize that this constant exposure to heat increases blood flow in the area and contributes to an increase in salivary rate flow.  An explanation for the decrease in the ratio of salivary rate flow as the number of years of handheld mobile phone use increased could be a compensation mechanism resulting from continuous insult to the dominant handheld mobile phones side.

This study found changes in the salivary secretion and protein concentration associated with handheld mobile phone use.

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