Letters to the Editor
To the Editor:
Divan et al1 found an association between behavioral difficulties in children and prenatal and postnatal mobile phone usage. They caution against assuming a causal relationship from exposure to electromagnetic fields from phones. Although this may be sensible regarding the weak fields to which the fetus would be directly exposed during maternal use of a mobile phone there are alternative mechanisms that warrant consideration.
Melatonin is a hormone that affects circadian rhythms and reproduction. Secretion of melatonin by the pineal gland is determined by exposure of the retina to light, but the neurologic pathway whereby this signal reaches the pineal gland is anatomically remarkable and potentially relevant to mobile phone exposures (Fig. 1 in Ref. 2). Nerve fibers leave the retina along the retinohypothalamic tract and reach the suprachiasmic nucleus. This nucleus does not send fibers directly to the pineal gland within the brain but stimulates the sympathetic nervous system via a pathway down the spinal cord and then to the superior cervical ganglion in the neck. Post ganglionic fibers ascend back into the brain by forming a plexus along the surface of the internal carotid artery, eventually to reach the pineal gland. The carotid artery is superficially placed near the angle of the jaw (where the pulse from it may be readily felt) and hence the sympathetic nerve fibers on it are also close to the skin. Mobile phones are commonly positioned so that the body of the phone is close to the angle of the jaw and hence to the nerve plexus. It is plausible that radiofrequency or extremely low-frequency fields from a mobile phone held close to the jaw may affect signaling in the unmyelinated nerves and in turn influence melatonin secretion.
Melatonin may affect reproduction and healthy fetal development in various ways.2,3 Secretion of melatonin is intrinsic to regulating normal circadian rhythms for temperature and metabolism. In addition, melatonin inhibits the secretion of gonadotropin-releasing hormone and may directly affect steroid metabolism within the ovaries and progesterone synthesis. Diverse changes in maternal metabolism or the sex hormone environment may affect development of the fetal brain leading to behavioral problems.
Melatonin is also closely related to changes in puberty, possibly because of its tonic inhibition of secretion of gonadotropin-releasing hormone during childhood. Interference with this normal restraining control pathway might also lead to altered behaviors in childhood and adolescence in children who use cell phones.
1. Divan A, Kheifets L, Obel C, et al. Prenatal and postnatal exposure to cell phone use and behavioral problems in children. Epidemiology. 2008;19:523–529.
2. Brzezinski A. Melatonin in humans. N Engl J Med. 1997;16:186–195.
3. Navara KJ, Nelson RJ. The dark side of light at night: physiological, epidemiological, and ecological consequences. J Pineal Res. 2007;43:215–224.
© 2009 Lippincott Williams & Wilkins, Inc.