"Chrono-functional milk": The difference between melatonin concentrations in night-milk versus day-milk under different night illumination conditions

Melatonin in Human Breast Milk and Its Potential Role in Circadian Entrainment: A Nod towards Chrononutrition?

Breastfeeding is the most appropriate source of a newborn's nutrition; among the plethora of its benefits, its modulation of circadian rhythmicity with melatonin as a potential neuroendocrine transducer has gained increasing interest. Transplacental transfer assures melatonin provision for the fetus, who is devoid of melatonin secretion. Even after birth, the neonatal pineal gland is not able to produce melatonin rhythmically for several months (with an even more prolonged deficiency following preterm birth). In this context, human breast milk constitutes the main natural source of melatonin: diurnal dynamic changes, an acrophase early after midnight, and changes in melatonin concentrations according to gestational age and during the different stages of lactation have been reported. Understudied thus far are the factors impacting on (changes in) melatonin content in human breast milk and their clinical significance in chronobiological adherence in the neonate: maternal as well as environmental aspects have to be investigated in more detail to guide nursing mothers in optimal feeding schedules which probably means a synchronized instead of mistimed feeding practice. This review aims to be thought-provoking regarding the critical role of melatonin in chrononutrition during breastfeeding, highlighting its potential in circadian entrainment and therefore optimizing (neuro)developmental outcomes in the neonatal setting.

The Effect of Short-Wavelength White LED Illumination throughout the Night on the Milk Fatty Acid Profile of High-Yielding Dairy Cows

Fatty acid levels in milk vary between day and night milking. Many dairy cows are still kept under white light-emitting diode (W-LED) illumination throughout the night, although it is known to disrupt endogenous circadian rhythms. We investigated the effects of whole-night W-LED illumination (125 lux) on milk yield and circadian composition, compared to a natural light−dark (LD) cycle of 10 h light. Mid−late lactation cows (n = 34) that were exposed to natural LD cycle showed circadian variation in milk fat composition, characterized by higher health-promoting monounsaturated fatty acid (MUFA; 24.2 ± 0.4 vs. 23.2 ± 0.4 g/100 g fat, p < 0.001) and lower saturated fatty acid levels (71.2 ± 0.4 vs. 72.5 ± 0.4, p < 0.001) at 13:30 h (day milk) than at 03:30 h (night milk). Compared to natural LD (n = 16), W-LED (n = 18) did not affect milk production or milk fat yields, yet abolished the milking time variation in milk fat composition towards a less healthy fatty acid profile. This lowered MUFA levels of day milk (23.8 ± 0.4 vs. 26.7 ± 0.4, p < 0.01). Therefore, W-LED has no commercial advantage over the tested natural LD cycle, and conversely, even shows circadian disruption. Accordingly, a natural LD cycle of 10 h light is preferable over W-LED from the perspective of cost savings, the cows’ well-being, and preserving the natural milk fat profile, as the nutritional value of the day milk is slightly higher.

Effects of SNPs in AANAT and ASMT Genes on Milk and Peripheral Blood Melatonin Concentrations in Holstein Cows (Bos taurus)

Aralkylamine N-acetyltransferase (AANAT) and acetylserotonin O-methyltransferase (ASMT), the two rate-limiting enzymes for melatonin synthesis, regulate melatonin production in mammals. Through analysis of the milk melatonin level and dairy herd improvement (DHI) index, it was found that the melatonin concentration in milk was significantly negatively correlated with the 305 day milk yield (305M) and peak milk yield (PeakM) (p < 0.05), while it was significantly positively correlated with the serum melatonin concentration (p < 0.05). The full-length of AANAT and ASMT were sequenced and genotyped in 122 cows. Three SNPs in AANAT and four SNPs in ASMT were significantly related to MT levels in the milk and serum (p < 0.05). The SNPs in AANAT were temporarily denoted as N-SNP1 (g.55290169 T>C), N-SNP2 (g.55289357 T>C), and N-SNP3 (g.55289409 C>T). The SNPs in ASMT were temporarily denoted as M-SNP1 (g.158407305 G>A), M-SNP2 (g.158407477 A>G), M-SNP3 (g.158407874 G>A), and M-SNP4 (g.158415342 T>C). The M-SNP1, M-SNP2, and M-SNP3 conformed to the Hardy−Weinberg equilibrium (p > 0.05), while other SNPs deviated from the Hardy−Weinberg equilibrium (p < 0.05). The potential association of MT production and each SNP was statistically analyzed using the method of linkage disequilibrium (LD). The results showed that N-SNP2 and N-SNP3 had some degree of LD (D′ = 0.27), but M-SNP1 and M-SNP2 had a strong LD (D′ = 0.98). Thus, the DHI index could serve as a prediction of the milk MT level. The SNPs in AANAT and ASMT could be used as potential molecular markers for screening cows to produce high melatonin milk.

Effects of the circadian rhythm on milk composition in dairy cows: Does day milk differ from night milk?

Metabolism in most organisms can show variations between the day and night. These variations may also affect the composition of products derived from livestock. The aim of the present study was to investigate the difference in composition between the day milk and night milk of dairy cows. Ten multiparous Holstein cows (milk yield = 25.2 ± 5.00 kg/d) were randomly selected during mid lactation. Milk samples were collected at 0500 h ("night milk") and 1500 h ("day milk") and analyzed to determine their composition. Mid-infrared spectroscopy was used to analyze macronutrient content of milk. Metabolomics and lipidomics were used to detect and analyze small molecules and fatty acids, respectively. An automatic biochemical analyzer and ELISA kits were used to determine biochemical indicators, as well as antioxidant and immune parameters in the milk. Though milk fat, protein, lactose, and total milk solids were not different between day milk and night milk, small molecules, metabolites and lipids, and hormones and cytokines differed between day milk and night milk. Regarding biochemical and immune-related indicators, the concentrations of malondialdehyde, HSP70, and HSP90 in night milk were lower than that in day milk. However, interferon-γ levels were higher in night milk. Additionally, night milk was naturally rich in melatonin. Lipidomics analyses showed that the levels of some lipids in night milk were higher than those in day milk. Metabolomics analyses identified 36 different metabolites between day milk and night milk. Higher concentrations of N-acetyl-d-glucosamine, cis-aconitate, and d-sorbitol were observed in day milk. However, the other 33 metabolites analyzed, including carbohydrates, lipids, AA, and aromatic compounds, showed lower concentrations in day milk than in night milk. The present findings show that the composition of night milk differs considerably from that of day milk. Notable changes in the circadian rhythm also altered milk composition. These results provide evidence to support the strategic use and classification of day milk and night milk.

The inhibitory effect of melatonin on human prostate cancer

Prostate cancer (PCa) is one of the most commonly diagnosed human cancers in males. Nearly 191,930 new cases and 33,330 new deaths of PCa are estimated in 2020. Androgen and androgen receptor pathways played essential roles in the pathogenesis of PCa. Androgen depletion therapy is the most used therapies for primary PCa patients. However, due to the high relapse and mortality of PCa, developing novel noninvasive therapies have become the focus of research. Melatonin is an indole-like neurohormone mainly produced in the human pineal gland with a prominent anti-oxidant property. The anti-tumor ability of melatonin has been substantially confirmed and several related articles have also reported the inhibitory effect of melatonin on PCa, while reviews of this inhibitory effect of melatonin on PCa in recent 10 years are absent. Therefore, we systematically discuss the relationship between melatonin disruption and the risk of PCa, the mechanism of how melatonin inhibited PCa, and the synergistic benefits of melatonin and other drugs to summarize current understandings about the function of melatonin in suppressing human prostate cancer. We also raise several unsolved issues that need to be resolved to translate currently non-clinical trials of melatonin for clinic use. We hope this literature review could provide a solid theoretical basis for the future utilization of melatonin in preventing, diagnosing and treating human prostate cancer.

Melatonin rich foods in our diet: food for thought or wishful thinking?

Melatonin continues to generate interest in the scientific community and the general public. In recent years, there has been growing interest in the possibility that melatonin present in human foods may have physiological effects. This has led to the promotion of "melatonin-rich" foods and "phyto-melatonin". The night time secretion of endogenous melatonin from the pineal gland provides a daily circadian signal which is detected by receptors in various tissues. In animals the changing circadian pattern of melatonin secretion across seasons is important to them to program their reproductive behaviours to ensure optimal reproductive success, while in humans it probably plays a prominent role in anchoring sleep to the night period. When melatonin is administered in non-physiological, milligram amounts to humans, the onset of sleep can be manipulated and in larger doses anti-oxidant properties may emerge. Melatonin-rich foods are considered in this context too, but the question remains whether the amounts of melatonin in the food can be expected to be high enough to realistically change sleep or have antioxidant properties. In this review, papers reporting the effects of ingestion of melatonin-rich food on plasma or saliva melatonin or its urinary metabolite are critically evaluated. Unfortunately many of the papers are compromised by poor experimental design and assay methodologies and uncritical evaluation of results. The conclusion drawn from this review is that it is wishful thinking to expect that the amount of melatonin in "melatonin-rich" foods will impact on sleep or have any other physiological impact.

Light Pollution, Circadian Photoreception, and Melatonin in Vertebrates

Artificial light at night (ALAN) is increasing exponentially worldwide, accelerated by the transition to new efficient lighting technologies. However, ALAN and resulting light pollution can cause unintended physiological consequences. In vertebrates, production of melatonin—the “hormone of darkness” and a key player in circadian regulation—can be suppressed by ALAN. In this paper, we provide an overview of research on melatonin and ALAN in vertebrates. We discuss how ALAN disrupts natural photic environments, its effect on melatonin and circadian rhythms, and different photoreceptor systems across vertebrate taxa. We then present the results of a systematic review in which we identified studies on melatonin under typical light-polluted conditions in fishes, amphibians, reptiles, birds, and mammals, including humans. Melatonin is suppressed by extremely low light intensities in many vertebrates, ranging from 0.01–0.03 lx for fishes and rodents to 6 lx for sensitive humans. Even lower, wavelength-dependent intensities are implied by some studies and require rigorous testing in ecological contexts. In many studies, melatonin suppression occurs at the minimum light levels tested, and, in better-studied groups, melatonin suppression is reported to occur at lower light levels. We identify major research gaps and conclude that, for most groups, crucial information is lacking. No studies were identified for amphibians and reptiles and long-term impacts of low-level ALAN exposure are unknown. Given the high sensitivity of vertebrate melatonin production to ALAN and the paucity of available information, it is crucial to research impacts of ALAN further in order to inform effective mitigation strategies for human health and the wellbeing and fitness of vertebrates in natural ecosystems.

Melatonin Stability in Human Milk

Introduction: Melatonin is an antioxidant, a circadian pacemaker, and an immune system stimulator. Studies have demonstrated beneficial effects of melatonin on various conditions in neonates. Melatonin is secreted in breast milk in circadian rhythm, but its half-life and stability in this medium and in real-life conditions of freezing and defrosting is unknown. The objective of this feasibility study was to evaluate stability of melatonin in breast milk after freezing and defrosting. Methods and Results: Breast milk samples of nocturnal milk and daytime milk were collected from 13 healthy breastfeeding mothers and were immediately frozen. Samples were defrosted in room temperature and were sampled for melatonin immediately and every hour for 4 hours and at 24 hours after defrosting. Melatonin levels were measured with Melatonin direct Saliva ELISA kit (IBL International).There was no statistically significant difference between levels at the different time points (p = 0.696). Melatonin levels in daytime milk were significantly lower than night-time levels (p = 0.028). Conclusion: Melatonin is stable in human milk for at least 4 hours after defrosting and even up to 24 hours. Further research of the therapeutic potential of night breast milk high in melatonin is needed.

Exogenous melatonin reduces somatic cell count of milk in Holstein cows

High somatic cell counts in milk caused by mastitis significantly influence the quality of milk and result in substantial annual economic loss. This study evaluated the beneficial effects of melatonin (MT) on milk somatic cell count (SCC) in cows. To examine the effects of melatonin on SCC, one hundred twenty cows were divided into four groups based on milk SCC. In each group, half of the cows were treated with melatonin (S.C.). Melatonin treatment significantly reduced milk SCC. To explore the potential mechanism, 20 cows with relatively high SCC were selected to evaluate the biochemical and immunological profiles of their blood after melatonin treatment. Treatment with MT significantly reduced SCC in milk, lowered serum cortisol concentrations and increased the levels of albumin, alanine transaminase and lactate dehydrogenase. Following treatment with MT, the concentration of IgG and IgM rose transiently then decreased significantly, similar to changes observed for white blood cells and lymphocytes. In conclusion, MT treatment improved the quality of milk by reducing SCC. This may be due to melatonin improving immune activity in cows.