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Late
nocturnal sleep onset impairs a melatonin shower
in young children
Jun
Kohyama, MD, PhD
Department
of Pediatrcs,
Tokyo Medical and Dental University, JAPAN
Key
words:
melatonin, late sleeper, sleep deprivation, antioxidant, melatonin
shower
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DEAR
EDITOR;
I
read an excellent review written by Reiter [1] with a great
interest.
The nocturnal sleep onset time in young children has progressively
become later in Japan, and now, nearly half of 3-year-old children
fall asleep later than 10 p.m. [2, 3]. The highest nighttime
melatonin levels during the whole life span is seen in the early
stages of life (1-3 years of age) [4]. Youngsters are flooded
by a "melatonin shower", although no one knows its
biological significance. My concern about the potential negative
physiological consequences of light exposure at an inappropriate
time especially during early stage of life is quite similar
to that pointed out by Reiter [1]. I hypothesized that children
who fall into sleep late in the night receive higher amounts
of light than those who fall into sleep early in the night,
and thus the melatonin levels of the late sleepers become lower
than those of the early sleepers.
To confirm this hypothesis, the relationship between the nocturnal
sleep habits and the melatonin levels was examined in youngsters.
Since both salivary melatonin concentrations and urinary 6-hydroxymelatonin
sulphate (6HMS) excretion rates are reliable indices of serum
melatonin concentrations [5], these non-invasively obtained
samples were measured. 6HMS concentration was expressed as a
function of creatinine excretion [6].
Fifty-six healthy 3-year-old children were studied. Informed
consent was obtained from the guardians of each child. The guardians
were asked to record sleep logs of the children for 7 consecutive
days, and to collect saliva (n=42) or urinary (n=14) samples
just after waking in the morning for any of three days during
the 7-day period of the recording. Saliva samples were asked
to collect before rinsing the mouth. Samples were stored at
-20°, and were measured by a radioimmunoassay by a commercial
company (SRL LTD.).
Among the 126 salivary samples collected, 109 samples had enough
saliva for the assay. Eighty-one samples showed melatonin concentrations
of less than 2.8 pg/ml. The mean sleep onset time on the night
before the collection of these 81 samples (9:41 p.m.) showed
no significance difference from that for the other 28 measurable
samples (9:30 p.m.). The mean wake-up time in the morning of
the 81 samples with undetectable melatonin levels tended to
be later (8:00 a.m.) than that for the 28 measurable samples
(7:36 a.m.) (t-test, 0.05<p<0.1).
Among
the 28 measurable saliva samples, the average melatonin concentration
in the 16 samples with sleep onset times of earlier than 10
p.m. (6.3 pg/ml) tended to be higher than that in the 12 samples
with later sleep onset times (4.8 pg/ml) (t-test, 0.05<p<0.1).
However, no statistically significant difference was obtained
between the 13 samples with wake-up times of earlier than 7:30
a.m. (5.6 pg/ml) and the 15 samples with later wake-up times
(5.7 pg/ml).
Among the 42 urinary samples collected, 38 samples were deserved
of measurement. The average urinary 6HMS concentration in the
samples with sleep onset times of 11 p.m. or later (178.5 ng/mg
creatinine) tended to be lower than that in the samples with
earlier sleep onset times (244.0 ng/mg creatinine) (t-test,
0.05<p<0.1). In addition, the average urinary 6HMS level
in the samples with wake-up times of 7:30 a.m. or earlier. (262.2ng/mg
creatinine) tended to be higher than that in the samples with
later wake-up times (208.0ng/mg creatinine) (t-test, 0.05<p<0.1).
The elevation tendency of melatonin in cases with earlier wake-up
times is likely to be due to a physiological drop of melatonin
levels in the morning by light. However, we found that the average
salivary melatonin and urinary 6HMS concentrations in the cases
with earlier sleep onset times tended to be higher than that
in the cases with later sleep onset times. This finding is consistent
with my hypothesis. In recent times, 24-hour-restless social
activity has become dominant. Young late sleepers have been
found to get less sleep than early sleepers [2, 3]. In addition
to this sleep deprivation, according to the current result,
young late sleepers are likely to suffer from the lack of a
"melatonin shower". Given that melatonin is a free
radical scavenger and antioxidant, free radical damage may be
aggravated by light suppression of melatonin levels [1].
Young late sleepers might suffer from the higher incidence of
cancer later in their lives.
REFERENCES
1.
Reiter RJ. REVIEW. Potential biological consequences of excessive
light exposure: melatonin suppression, DNA damage, cancer and
neurodegenerative diseases. Neuroendocrinol Lett 2002; 23 Suppl
2:9-13.
2. Kohyama J, Shiiki T, Hasegawa T. Sleep duration of young
children is affected by nocturnal sleep onset time. Pediatr
Int 2000; 42:589-591.
3. Kohyama J, Shiiki T, Ohinata SJ, Hasegawa T. Potentially
harmful sleep habit of 3-year-old children in Japan. J Dev Behav
Pediatr 2002; 23:67-70.
4. Waldhauser F, Weiszenbacher G, Tatzer E, Gisinger B, Waldhauser
M, Schemper M, Frisch H. Alterations in nocturnal serum melatonin
levels in humans with growth and aging. J Clin Endocrinol Metab
1988; 66:648-652.
5. Nowak R, McMillen IC, Redman J, Short RV. The correlation
between serum and salivary melatonin concentrations and urinary
6-hydroxymelatonin sulphate excretion rates: two non-invasive
techniques for monitoring human circadian rhythmicity. Clin
Endocrinol 1987; 27:445-452.
6. Young IM, Francis PL Leone AM, Stovell P, Silman R. Constant
pineal output and increasing body mass account for declining
melatonin levels during human growth and sexual maturation.
J Pineal Res 1988; 5:71-85.
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