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.