Melatonin is responsible for circadian regulation and the control
of sleep, encountered in the organism at highest concentrations
during the night.1 With aging, there is a substantial reduction in
melatonin production, which may impair sleep quality among the
elderly.2
Melatonin is naturally present in many foods including cherry,
banana, peppermint, red wine, and milk.3 It is not considered as
a food additive by the Harmonized General List of Food Additives
and their Functional Classes of the Mercosur,4 thus not permitting
it to be included as food.
Cow’s milk contains roughly 5 pg mL−1 of melatonin, and studies
have focused on naturally increasing the melatonin concentration
by using different milking techniques. Valtonen et al.5 showed
that it is possible to increase the concentration of melatonin up
to 56.4 pg mL−1 with changes in the photoperiod of cows; that
is, by increasing the period in which the animals remain in the
dark for 17 h. Haigh6 increased the concentration of melatonin in
milk to 35 pg mL−1 by night milking, with maximum illumination
of 50 lux; Gnann7 developed a method for naturally increasing
melatonin in milk by night milking animals exposed to light at
different wavelengths during the day and at night.
Tryptophan is an essential amino acid, a precursor of melatonin
synthesis by the pineal gland, and acts to improve sleep and
reduce stress and antioxidant effects. Tormo et al.8 and Sanchez
et al.9 demonstrated that it is possible to increase the concentration
of plasma melatonin by tryptophan administration. However, no
studies in the literature have described an increase in plasma
melatonin concentration because of the addition of tryptophan
to milk.
Also, no studies have been reported on the concentration of
melatonin in the milk of cows in Brazil. However, it is known that
melatonin concentration in milk varies with the breed, nutrition,
stress level of the animals, and ambient temperature.10 This
work aimed to evaluate the melatonin concentration in milk
collected by night milking and to evaluate its effect, with our
without tryptophan supplementation, in the sleep quality of adult
Wistar rats