DII calculation
A complete description of DII has been provided by Shivappa et
al.25 The index is based on 1943 articles published
since 1950 to 2010 and measures the effects of 45 dietary parameters on
six inflammatory biomarkers. (IL-1β, IL-6, TNF-α, CRP, IL-4, and IL-10).
In fact, each one of these dietary factors received a negative score
(-1) if its impact was anti-inflammatory (significantly increased IL-4
or IL-10, or reduced IL-1β, IL-6, TNF-α, CRP), a positive score (+1) if
its impact was pro-inflammatory and 0 if no significant changes was
observed in biomarkers. To calculate the DII score, each study
participant’s dietary data was first linked to the global database that
provided a robust estimate of a mean intake and a standard deviation for
each of the 45 food parameters. In this study, of the 45 possible food
items in the DΠ list, dietary intakes of 30 food parameters including
energy, protein, carbohydrates, fiber, total fat, saturated,
monounsaturated and, polyunsaturated fatty acids, omega 3 and omega 6
fatty acids, trans fats, cholesterol, vitamins A, beta carotene, E, D,
C, B1, B2, B3, B6, B12, folate, zinc, selenium, magnesium, Iron (Fe),
garlic, onion, and caffeine, were applied to compute the DII. To obtain
the z-score, the mean global for each food parameter was subtracted from
the actual intake of each food parameters and then divided by its
standard deviation. To minimize the effect of “right skewing,” Z
scores were converted to the centered proportion score as multiplied by
2 and subtracting 1. To acquire the food parameter-specific DII score,
the final value was multiplied by its respective overall food parameter
score. Subsequently, the DII score was computed by summing all food
parameter-specific DII scores. The higher DII score, the more
pro-inflammatory diet, while a more negative value indicated a more
anti-inflammatory diet. The theoretical maximum range of DII scores was
from about -8.87 to about +7.9821,25.
Assessment of sleep quality
To assess sleep quality, we applied the 18 self -reported items in
Pittsburgh’s sleep quality index (PSQI) 26. The PSQI
questionnaire was generated by Buysse et al. for assessment of sleep
quality and detection of sleep disturbances and involved 7 subscales,
including subjective sleep quality, sleep latency, sleep duration, sleep
efficiency, sleep disturbances, use of sleep medication and daytime
dysfunction. Scales of each subscale is ranged from 0 to 3. Moreover,
the total score of these 7 parts ranges from 0 to 21. The global PSQI
score over 5 is considered as poor quality of sleep. Participants were
asked to respond their bed time and wake time to the nearest hour and
the times were then used to compute duration of
sleep39. Validity and reliability of this
questionnaire have been investigated in Iran (α = 0.83 and correlation
coefficient = 0.88)40.