The objective of this study was to observe the association between modified Nordic diet with sleep quality and circadian rhythm in overweight and obese woman. Our hypothesis was that a higher adherence to the modified Nordic diet score, which represents a healthy dietary pattern, is connected with better sleep quality over time. This result adds a new insight into the relationship and possible pathways between sleep and diet.
In present study, the results showed a reverse association between adherence to modified Nordic diet and poor sleep quality status. Moreover, a significant positive association was observed between the completely morning and modified Nordic diet. also, a significant reverse association was observed between completely evening type and modified Nordic diet.
Previous finding on the correlation of diets with sleep quality and circadian rhythm has been obtained mostly from cross sectional studies. One study shows short sleep duration combined with poor sleep quality is associated with low adherence to a Mediterranean diet and Nordic diet (25).
Melatonin could modulate circadian rhythm and improve sleep disorders (30-32). The interpretation is that melatonin weakens the circadian signal from the suprachiasmatic nuclei (SCN), promoting heat loss which induces sleepiness via the preoptic area of the anterior hypothalamus (33). It has been proved that the melatonin concentration in human serum could significantly increase after consumption of melatonin containing food like fruits and vegetable (34). In animal foods, melatonin concentrations were found higher in fish than those in meat (35). Other research showed calcium along with magnesium and potassium act neuromodulators in the sleep/wake cycle and may play an important role in melatonin production through the activation of tryptophan hydroxylase (36, 37). Many micronutrients play a role in sleep and circadian regulation, including those that support melatonin synthesis (folate, vitamin B6, zinc) (38). a study shows a greater percentage of all adults reporting short sleep had inadequate intake of copper, folate, iron, magnesium, riboflavin, zinc, and vitamins A, C and K (39). Intracellular magnesium concentration acts as a cell-autonomous timekeeping component to determine key clock properties in human cell lines and unicellular alga (40). In addition, magnesium has an essential role in ion transport and electrical conductivity, which facilitate N-methyl-D-aspartic acid (NMDA) receptor function, an important sleep regulator (41). Magnesium may also play a role in melatonin synthesis as a cofactor for serotonin N acetyltransferase (arylalkylamone-N-acetyltransferase; AANAT), which facilitates the conversion of serotonin to N-acetylserotonin, the rate limiting step in melatonin synthesis (42). In one study shows less calcium intake associated with greater difficulty falling asleep and less carbohydrate intake associated significantly with greater difficulty maintaining asleep and less potassium intake associated with greater daytime sleepiness and less calcium and vitamin C intake associated significantly with greater non-restorative sleep (43). Fewer sleep difficulties associated with increased calcium may have been a result of the effects of calcium on lowering blood pressure (44). Animal models of melatonin-proficient (C3H) and melatonin-deficient (C57BL) mice are often used to investigate the role of melatonin in circadian rhythms. In one study, a study was performed on three clock gene proteins, PER1, BMAL1 and CRY2, in the adrenal cortex of mice and medulla, and the results showed that C3H, PER1 and CRY2 mice reached a maximum in the light phase while BMAL1 peaked in the dark phase, these three clock gene protein levels showed day / night changes in both the adrenal and medullary cortex. Similar patterns were shown in the adrenal cortex of C57BL mice, but in the adrenal cortex of C57BL mice, the clock gene protein level was consistently lower than that of C3H mice and did not change over time (45). The effect of polyphenols on sleep measures may be through their antioxidant content reducing oxidative stress and improving sleep quality (46). St-onge suggested that plant based diets may improve sleep quality (47). In one study, polyphenol-rich food supplement was able to significantly improved sleep quality by 43% (48). A study shows inverse association between fruits and vegetable consumption and poor sleep quality (49). A study shows low intake of vegetables and fish, high intake of confectionary and noodles and unhealthy eating habits were independently associated with poor sleep quality (50). The first potential mechanism of how polyphenols from fruits and vegetables consumption may affect sleep measures is through the gut–brain axis via serotonin and γ-aminobutyric acid (GABA) receptors, consequently affecting nocturnal secretion of melatonin (51). Polyphenols in red cabbage extracts decreased sleep onset latency (SOL) and increased sleep duration via γ aminobutyric acid GABA receptors in mice (52). Low protein intake (<16 % of energy from protein) was associated with poor quality of sleep and marginally associated with difficulty initiating sleep, whereas high protein intake (>19 % of energy from protein) was associated with difficulty maintaining sleep. low carbohydrate intake (<50 % of energy from carbohydrate) was marginally associated with difficulty maintain sleep and when stratified by sex, these association were significant in men not in women (53). Higher consumption of meat was also associated with incidence of snoring and poor general sleep quality (50). An increase in fish intake in associated with further improvement the quality of sleep (54). Dietary fat and protein and too much smaller carbohydrate stimulate the release of cholecystokinin (CCK) in duodenum and jejunum (55). Post prandial release of CCK induce sleepiness in healthy adult 2 to 3 hours after high fat and low carbohydrate meal (56). Finally, we can say that in this study, the reason for the effect of modified Nordic diet to increase the quality of sleep due to more significant consumption of fish, root vegetable, cabbages, apple pear, vegetables, fruits, Eicosapentaenoic acid (EPA), Docosahexaenoic acid (DHA), potassium, magnesium, calcium, zinc, iron, B6, vitamin C, fat, carbohydrate.
What is already known on this subject?
Recent studies show that modified Nordic diet has emerged as a healthy eating option. Before present study, very limited studies conducted the association between modified Nordic diet and sleep. The reason we conduct the association between the modified Nordic diet and sleep is the reduction of sleep duration over the past 60 years (5) and also insomnia is a common clinical condition, characterized by difficulty initiating or maintaining sleep, with a prevalence of 10%-20% (6). Data from current study suggest those who had good quality sleep had higher adherence to a modified Nordic diet.
What does this study add?
No previous studies have been conducted relating modified Nordic diet and sleep in the Iranian population. We provide evidence that it may be one of the better predictors of the relationship between diet and sleep.
Limitations and strengths
It was cross-sectional; hence causality cannot be evaluated. Small population and the same-sex sample also limit the statistical power. Dietary assessment by FFQ questionnaire can result over- or under-reporting food intake. Due to low adherence to Nordic diet in Iranian population, we could not use the original Nordic diet scored and we replaced the modified Nordic diet score. Due to the different culture and dietary intakes, our results are not possible to generalize through the country. No previous studies have been conducted association between modified Nordic diet with sleep quality and circadian rhythm in the Iranian population. We provide evidence that it may be one of the better predictors of association between diet and sleep quality.