A cross-sectional study involving 19317 participants was conducted in this study. The results show that the positive correlation between DII and CKD is independent of the following covariates such as age, gender, race, poverty-income ratio, body mass index, SBP, DBP, current smoking, alcohol intake, FPG, albumin, triglyceride, total cholesterol, high density lipoprotein, low density lipoprotein, diabetes, antihypertensive drugs, lipoprotein-lowering drugs and hypoglycemic drugs. There is a linear positive correlation between DII and CKD in women, not men.
Previous studies related to DII and CKD are limited, with only two studies. Rouhani and his colleagues[16] evaluated the association between DII and renal function indicators and the progression of kidney disease in 221 patients with CKD; This study shows that DII has nothing to do with renal function indexes (blood urea nitrogen (BUN) and serum creatinine (Cr) as well as eGFR) in the fully adjusted model; however, higher DII scores are significantly related to the increased risk of CKD progression ( OR:2.12 ; 95%CI: 1.05, 4.26). The large cross-sectional study conducted by Mazidi[17]et al. included 21 649 participants. The purpose of this study was to investigate the relationship between DII and renal function and CKD prevalence among American adults. The main conclusions are as follows: the increase of DII level is positively correlated with the increase of urinary albumin, uric acid, creatinine and the decrease of eGFR, and the prevalence of CKD in the highest DII quartile was 29% higher than that in the lowest DII quartile. Pro-inflammatory diet is related to decreased renal function and high prevalence of CKD.
We found that our results are consistent with the above studies. However, this study found the gender difference between DII and CKD for the first time. In our study, we found that the positive correlation between DII and CKD prevalence only appeared in women, not men. As shown in Table 2, in the fully adjusted model, the prevalence of CKD increased by 25% for every standard deviation of DII level of female participants. When DII was transformed into a categorical variable, the participants in the lowest group Q1(DII < 0.63) served as the reference group, and the participants in the highest group Q4 (DII ≥ 3.27) increased the risk of CKD by 73% (P for trend < 0.05). Among men, DII has no relationship with CKD, whether it is a continuous variable or a categorical variable.
For the time being, the underlying pathological process between DII and CKD is not clear, so here's a guess. Pathological and physiological process of CKD is based on low-grade chronic inflammation[5]. Inflammation, coagulation dysfunction and neutrophil-endothelial cell interaction are considered to play a role in the occurrence of kidney damage, which may lead to chronic kidney damage[25]. It may be that diet plays an important role in regulating chronic inflammation [26]and kidney health. The design of DII is used to evaluate different anti-inflammatory and pro-inflammatory dietary components and quantify dietary inflammation. Therefore, with the increase of DII, the risk of CKD prevalence rate is significantly increased. From Table 1, we can see that women's DII level, BMI, TC, HDL, LDL level are higher than those of men, but the drug use rate of glucose-lowering drugs and lipoprotein-lowering drugs of women is lower than that of men. Studies have shown that the level of CPR in American women is much higher than that in men [27], so it is more likely that they will have chronic inflammatory reaction. Further investigation is needed to determine the biological and psychosocial factors behind these gender differences.
There are several limitations in our research. First of all, this study is a cross-sectional study, and the causal relationship between DII and CKD cannot be obtained. Secondly, the results may be confused by unmeasured factors, such as structural or functional kidney abnormalities, and some environmental or occupational exposures. Finally, this study was carried out in the American population, and the results could not be extended to other populations.