Discussion:
In the present study, the relationship between DASH, DII and HEI score with sum sleep and time in bed was assessed, in the employees.
The results of the present study showed that there is a positive association between DASH score and time in bed; also, there is a strong negative association between HEI score and sum sleep, and a strong positive association between HEI score and time in bed. But we noticed a positive association between DII score and sum sleep. It means that by increasing HEI and DASH score, sleep quality increases, but by increasing DII score, the sleep quality decreases.
There are several studies that have surveyed the relationship between sleep quality and diet quality.
Similar to our study, Liang et al. In a study of 3941 American adults found that following a dash diet could effectively improve sleep quality and sleep duration(24). Also, similar to our study, Mossavar-Rahmani in a study of 2,140 Spanish adults found that increasing the Healthy Eating Index effectively increased sleep duration and sleep efficiency(25). Also, another study conducted on 1500 adults in Spain, showed a lower variation in sleep duration, and lower sleep quality, in the individuals, adherent to the Mediterranean diet(26). Another study conducted by Jaussent et.al found a positive effect of Mediterranean pattern on specific aspects of sleeping(27). Consumption of fruits, legumes, nuts and fish is an important factor in the indication of Healthy Eating Index and following a DASH diet(22). Various studies have shown that these factors can be effective in improving sleep quality. Jyväkorpi et al. Showed that eating vegetables helps to sleep better(28). Hakkarainen et al. Also showed that people with insomnia eat less vegetables(29). Kurotani et al. And Cao Y et al. Showed that consumption of vegetables, fruits and legumes is associated with better sleep quality(30, 31). Liang et al. Also found that reduced consumption of vegetables, nuts, and legumes was associated with reduced sleep duration(24). Other studies also confirm that consumption of fruits and vegetables is directly related to sleep duration and sleep quality(26, 32).
In addition, Jyväkorpi et al. And del Brutto et al. Showed that fish consumption can be effective in improving sleep duration(33). Kurotani et al. Also showed that fish consumption can reduce the PQS (poor quality of sleep) score(30) and nutrition showed that fish is related to sleep timing(34).
Refined grains, Sodium, Added Sugars and Saturated Fats are factors that reduction of their consumption can increase the score of the Healthy Eating Index(22). Sodium is also important in determining the score of dash diet(35). Mossavar-Rahmani et al. showed that among the components of AHEI-2010, decreased sodium intake was most strongly associated with higher sleep efficiency (25). Grandne et al. Showed that sugar consumption was directly related to poor sleep quality(36). Kant et al. Also showed that consuming Sugars during sleep is also effective(37). Jyväkorpi et al. Also showed that consumption of Sugars and Saturated Fats are associated to poor sleep quality(28). Moreover, other animal and small human experimental studies have shown that high-saturated-fat diets may influence in circadian rhythms(38, 39). Other studies with results aligned to our study, showed that higher DII scores are negatively associated with sleep quality.
In a recent study by Lopes et al, it was shown that the DII score was only positively associated with daytime sleepiness as a component of PSQI(40). In the study by Godos et al, participants in the highest quartile of DII score were more likely to have poor sleep(41).
An interventional study also showed that an anti-inflammatory diet including increased intake of fruits, vegetables, lean protein, and reduced intake of added sugars and SFAs could improve sleep quality(42).
There are some possible explanations for the mechanisms underlying the inverse association between sleep quality and the healthy pattern, one of the explanations is that proteins include tryptophan that is a component of serotonin production and neurosecretory hormone melatonin. sleep cycle, either directly or indirectly, and brain function is controlled by Serotonin(43).
Generally, serotonin promotes wakefulness, also regulates sleep through changes in the concentration of melatonin(43, 44). Melatonin exerts a hypnotic effect through thermoregulatory mechanisms by lowering the core body temperature, reducing arousal and increasing sleep-propensity(44).
Also, vitamin B6, pyridoxine, is required for the synthesis of serotonin from tryptophan(45). The 5-Hydroxytryptophan is an intermediate in this process, and is converted to serotonin by a pyridoxal 5′-dependent enzyme(44, 45). In relation, dietary niacin is involved in leaving more tryptophan to be used for the synthesis of serotonin(46).
In addition, folate is involved in the metabolism of monoamines like serotonin in the brain(46). The N-3 fatty acids are required to convert serotonin to melatonin by the enzyme arylalkylamine-Nacetyltransferase(44).
Other nutrients such as Magnesium enhances the secretion of melatonin from the pineal gland by stimulating serotonin N-acetyltransferase activity, which is the key enzyme in melatonin synthesis(47). B12 also increases melatonin receptors in the brain(48).
In addition, oxidative stress can lead to insomnia(49). Diets with rich in antioxidant vitamins including vitamin C, have a high score of the healthy dietary pattern, which may decrease the levels of oxidative stress and prevent the development of DIS. Therefore, the above-mentioned nutrients or their combination might have a beneficial role in initiating sleep.
Increased HEI and DASH scores are associated with increased protein intake resulting in increased tryptophan. Diets with higher DASH and HEI score, contain more dark green vegetables, fruits, nuts and seeds(22, 23).
As a result, it increases the intake of magnesium, folate and vitamin C and other antioxidants from the diet, which are important factors in regulating effective hormones in sleep(30).
Diets with higher HEI and DASH scores have more variety of foods, and contain whole grains that are high in B vitamins, so they can help individuals with their sleep quality.
Increasing fish intake increases omega-3 and b12 fatty acids, which improve sleep quality(48). Fish also contains glycine, which studies show can improve sleep satisfaction(50).
Decreasing the DII score of a diet indicates the anti-inflammatory properties of the diet, which together with increasing the consumption of nutrients such as magnesium, niacin B6, B12, folate, vitamin C and omega 3, are effective in regulating melatonin(44).
Other anti-inflammatory agents that have been shown to be effective in improving quality and sleep time include potassium, fiber, and calcium(24, 30, 51).
Studies have also shown that some nutrients that have inflammatory properties in the DII index, play an important role in reducing sleep duration and sleep quality. These nutrients include total fat, SFA and cholesterol(52, 53).
One of the reasons that increased DII scores, results in decreased sleep quality, may be because of the increase in CRP levels, that is related to increased sleep apnea. Also, researchers have found that inflammation and inflammatory factors are positively linked to oxidative stress; these factors include advanced-glycation end products like erythrulose that decreases sleep quality.
One of the strengths of this study is that no such study has been conducted in the south of Iran, about dietary scores and sleep quality, also no study has been done to evaluate the food and nutrition of employees and that the results of this study provide conditions for other studies. But there are limitations to this study, too. We could not cover different ethnicities and our sample size was limited to Jundishapur University and other university centers in the province were not surveyed; also, the sample size of the study reduced the original sample size by excluding very high and low calories.