The authors carried out two studies on male electric utility workers. Both had the same study design. Study 1 had 149 participants and Study 2 had 77, each of whom collected urine samples and recorded cell phone use over 3 days. The majority of cell phones used were analogue. Personal 60-Hz magnetic field and ambient light exposures were also recorded. The urine samples were examined for 6-hydroxymelatonin sulfate (6-OHMS), an indicator of melatonin output from the pineal gland.
The results were analyzed for 4 groups, depending on volume of cell phone use - 0, 1-10, 10-25, and >25 minutes per day. No difference was found in Study 1 between high users and non-users of cell phones. Only 3 subjects reported >25 minutes use per day. In Study 2, five participants used cell phones for >25 minutes per day (13 worker-days total). This high use was associated with lower nocturnal 6-OHMS urinary excretion. There was a significant decreasing trend of 6-OHMS excretion as cell phone use increased in the different categories. However, it was only on the third day that those with >25 minutes/day had statistically different mean nocturnal 6-OHMS excretion compared with those in the no-use category.
In Study 2, workers in the highest category of cell phone use who were also in the top third of workplace 60-Hz exposure had lower nocturnal 6-OHMS excretion compared with those with high telephone use but low 60-Hz exposure. Similarly, among workers in the top third of workplace 60-Hz exposure, those with higher phone use had lower overnight excretion of 6-OHMS than those with no cell phone use.
conclude that cell phone use may be associated with decreased nocturnal
excretion of melatonin. They suggest that, since the effect was only seen
on the third day of participation, a minimum daily and/or a multi-day
threshold of phone use may be necessary to reduce 6-OHMS excretion. It
is not clear if those using cell phones did so for the first time while
participating in the study. If not, then the decreased excretion of 6-OHMS
seen on the third day is difficult to explain. The authors state that
"uncertainties about RF exposures and the small proportion of workers
with extensive cellular telephone use limit the interpretation of our
results". Also, non-work cell phone use was not determined.