Epidemiological studies have suggested that dyslipidemia is associated with a reduced eGFR, but the specific types of lipids or lipoproteins that contribute to eGFR remained unclear for the general Chinese population. Based on the weighted data from a national representative population of 16,206 Chinese individuals, we found that the estimated mean eGFR values were significantly lower with TG levels in the abnormally high categories, and the prevalence rates of mildly impaired eGFR and moderately/severely impaired eGFR were significantly higher with TG levels in the abnormal categories (1.7 ~ 2.3, ≥ 2.3 mmol/L). The estimated prevalence of mildly impaired eGFR was also higher with LDL-C levels in the borderline high category (≥ 4.1 mmol/L). The results further indicate that high TG and low HDL-C were independently associated with a lower eGFR, whereas high TC and LDL-C were independently associated with a higher eGFR after adjustment for age, gender, BMI, smoking, alcohol intake, diabetes, and hypertension. Using multinomial logistic analyses, the TG level significantly contributed to the elevated risks for impaired eGFR. Moreover, a reduced HDL-C had a significantly stronger impact on eGFR in males, overweight/obese individuals, and those with smoking or alcohol intake habit. The findings of the present study highlight the importance of lipid and lipoprotein measurement in the risk assessment and prevention of impaired renal function in the general Chinese population, independent of the other conventional risk factors. A personalized management strategy for the at-risk population with recognition of the other conventional risk factors must be emphasized.
CKD is well known to be associated with an increased risk for cardiovascular events. In fact, previous studies indicated that a mild reduction in eGFR increases the risks for cardiovascular morbidity and mortality. For example, an observational study suggested that the risks for cardiovascular events and all-cause mortality increased in participants with an eGFR of 60 ~ 89 mL/min per 1.73 m2 compared to those with an eGFR ≥ 90 mL/min per 1.73 m2(20). In the Chinese population, the REACTION study reported that even a mildly reduced eGFR (< 90 mL/min per 1.73 m2) is associated with an elevated 10-year Framingham risk for coronary heart disease and an elevated 10-year atherosclerotic cardiovascular disease risk among Chinese adults(2). At the same time, several studies established that monitoring of eGFR at a normal or milder stage is of clinical importance. In a community-based Chinese population aged over 40 years with normal or mildly impaired renal function, 12.3% of the participants developed renal function decline during a 4-year follow-up with a median change in the eGFR of ~ 20 mL/min per 1.73 m2(21). Sumida et al. reported that 12% of the participants in a nationwide cohort of 56,946 United States veterans with an eGFR ≥ 60 mL/min per 1.73 m2 showed rapid eGFR decline (≥ 5 ml/min per 1.73 m2/year)(22). Interestingly, another study conducted in a US population found that 348 of 2,219 individuals with an eGFR of 60 ~ 119 mL/min per 1.73 m2 showed rapid renal function decline (≥ 5 ml/min per 1.73 m2/year) in an 8-year follow-up, and a greater percentage experienced rapid renal function decline among individuals with a baseline eGFR of 60 ~ 89 mL/min per 1.73 m2 versus a baseline eGFR of 90 ~ 119 mL/min per 1.73 m2(23). These facts also support that individuals with mildly impaired renal function will experience more rapid renal function decline, making them major candidates for CKD in the future. In the present study, the estimated prevalence rates of both mildly impaired eGFR (60 ~ 90 mL/min per 1.73 m2) and moderately/severely impaired eGFR (< 60 mL/min per 1.73 m2) were reported, and both outcomes were considered in the analyses applying the multinomial logistic procedure in SUDAAN software. Thus, the findings of the current study provide valuable information for the prevention of CKD in the general Chinese population aged 20 years and older.
Lipid disorder is proposed to be an essential cause of renal dysfunction, and patients with renal dysfunction usually have concomitant dyslipidemia. However, the link between lipid metabolism and the GFR have not been fully elucidated. Experimental data show that dyslipidemia can affect renal function and accelerate the progression of renal injury(24). Altered fatty acid and cholesterol metabolism are known as the key mediators of renal lipid accumulation, resulting in renal inflammation, oxidative stress, and fibrosis(25). Clinical studies showed that lipids or lipoproteins have discordant contributions to the GFR. Previous studies frequently showed that an increased TG level and a decreased HDL-C level were associated with a decreased eGFR, as well as the risk for renal dysfunction, in several different populations(6, 7, 9–11). However, there has been a lack of research based on nationally representative general populations. In the current study, we estimated the prevalence rates and investigated the contributions of lipids and lipoproteins to eGFR and the risks for eGFR impairment in a nationally representative Chinese population with a large sample size, which was also weighted to represent the total population of Chinese adults on the basis of population data and sampling scheme. Thus, the results from this study can be reliably generalized to the general population of Chinese ancestry.
Our results demonstrated significant contributions of abnormal TG and HDL-C levels to decreased eGFR, as well as the contribution of high TG to elevated risks for both mildly impaired eGFR and moderately/severely impaired eGFR. The present study also emphasizes the importance of reducing TG and raising HDL-C for renal function protection in the general population. In this respect, drugs targeting TG or HDL-C, such as fibrate compounds, niacin, and inhibitors of cholesteryl ester transfer protein, might be beneficial theoretically. Evidence of their impacts on kidney function is still lacking. In current clinical practice, fibrate and niacin are only recommended for the treatment of patients with TG ≥ 5.7 mmol/L to prevent pancreatitis, and for the treatment patients who were previously treated the maximum tolerable doses of statins and continued to have TG ≥ 2.6 mmol/L(18, 26). However, in the FIELD Helsinki study, even concomitant decreases in creatinine clearance and eGFR in type 2 diabetes patients were revealed after long-term fenofibrate treatment for 5 years(27). Similar findings were also reported in outpatients not restricted to those with diabetes(28). In the future, clinical trials focusing on renal outcomes of drugs targeting TG or HDL-C are highly anticipated.
We previously reported that BMI, waist circumference, blood pressure, and fasting and post-prandial glucose levels are associated with TG in the Chinese population, whereas BMI, waist circumference, and glucose levels are associated with the HDL-C level(29). Interventions treating metabolic disorders are also well-known to be beneficial for the protection of renal function in Chinese populations. However, the findings of the present study indicate that TG and HDL-C influence renal function independent of the conventional risk factors including age, smoking and drink habits, as well as metabolic-related disorders, such as obesity, abnormal glycemic metabolism and hypertension. Thus, the present study highlights the critical impacts of TG and HDL-C on renal function beyond those conventional risk factors, indicating that these levels should be closely monitored and controlled.
Elevated TC and LDL-C levels are the predominant features of lipid disorder in patients with nephrotic syndrome. However, the exact influences of TC and LDL-C on the eGFR continue to be debated. The conflicting results from different studies could have resulted from the differential adjustment for confounding factors or differences in the study populations. For instance, without controlling for the other conventional factors, negative correlations were observed between TC or LDL-C and eGFR in a Chinese population aged 40 years or older(7). In another study based on middle-aged and elder Chinese population, TC was associated with a decreased eGFR before and after adjustment for the conventional risk factors, and LDL-C was only associated with a decreased eGFR in the crude model(8). Moreover, other studies failed to identify any associations of TC or LDL-C with a decreased eGFR(9, 10). Notably, the CRIC study reported that a 1-standard deviation (SD) higher TC or LDL-C was associated with a 26% or 23% lower risk, respectively, of the renal end point after adjustment the other risk factors in patients with low levels of proteinuria (12). In the current study, among those with an abnormally high TC or LDL-C, the prevalence of eGFR impairment tended to be increased, suggesting that eGFR should be carefully monitored in individuals with abnormally high TC or LDL-C in clinical practice. On the other hand, after adjustment for the conventional risk factors, both elevated TC and LDL-C levels were independently associated with an increased eGFR, as well as lower risks for eGFR impairment. Although it cannot be determined whether causal relationships exist between TC or LDL-C and eGFR in the Chinese population via this cross-sectional study, it can be speculated that metabolic factors, such as BMI, diabetes status, and hypertension, have strong interplay with TC or LDL-C, leading to conflicting findings with or without adjustment for these factors. Moreover, the absolute roles of elevated TC and LDL-C independent of the other comorbid metabolic disorders may be protective of eGFR. In addition, statins, which are widely used to lower cholesterol levels by inhibiting the enzyme HMG-CoA reductase, have long been speculated to protect kidney function(4, 5). A recent meta-analysis conducted in 2016 reported that statin therapy does not reduce the risk for kidney failure events in adults not receiving dialysis, but may modestly reduce proteinuria and the rate of eGFR decline(30). Thus, the exact biological effects of TC and LDL-C on the eGFR remain incompletely understood.
Using interaction and subpopulation analyses, a decreased HDL-C was observed to have significantly stronger influences on the reduction of eGFR and elevated risks for impaired eGFR in males and individuals with smoking or alcohol intake habit, as well as a stronger influence on the reduction of eGFR in overweight/obese individuals. These results suggest that the disturbance of HDL-C can be more harmful, especially for these patient groups. In the Chinese population, the majority of the individuals with smoking or alcohol intake habits are men, which may partly explain the similar patterns of the interacting effects of these factors. Notably, because smoking and alcohol intake are modifiable factors, lifestyle intervention, such as smoking cession and alcohol avoidance, might reduce an individual’s risk for renal dysfunction through the interaction with HDL-C. Based on the observation that the eGFR of overweight or obese individuals was more susceptible to the reduction of HDL-C, these patients may also benefit from weight loss intervention. Moreover, each per mmol/L TG increase significantly increased the risk for moderately/severely impaired eGFR by 45% specifically in males, but not in females, suggesting that males were more susceptible to the effects of increased TG. We also found that the protective role of TC against mildly impaired eGFR did not exist among individuals with prediabetes or diabetes. Also, the protective effect of LDL-C was observed only in the middle-aged population (40 ~ 60 years old). Overall, the interaction data highlight the necessity of personalized management of the eGFR for the prevention of CKD.
The current study has the following strengths. The present study was based on a relatively large nationally representative survey in China, and the data were weighted on basis of the population data and sampling strategy, so that the results could be well-generalized to the Chinese population. Second, the mild eGFR impairment was taken into consideration by applying a multinomial logistic regression analysis, which provided valuable data for the early prevention and intervention of renal function decline. Finally, the elucidation of interaction effects of conventional factors can be applied to achieve precise risk assessment and improve intervention strategies. However, this study also has limitations. As a cross-sectional survey, it could not elucidate the sequential effects of the onset of dyslipidemia and eGFR impairment. Therefore, longitudinal studies are required to test the robustness of the findings of this study. Moreover, accumulating data for the involvement of lipid composites besides TC, TG, HDL-C, and LDL-C are found in the literatures(31, 32), suggesting that novel lipid biomarkers for eGFR not covered in the present study still need to be investigated.
In summary, we investigated the contributions of the four clinical measurements of lipids and lipoproteins on eGFR, as well as the risks for mild eGFR reduction and moderate/severe eGFR reduction based on weighted data from a nationally representative general population of Chinese ancestry. Significant increases in TG, TC, and LDL-C were accompanied by a decrease in the eGFR. With adjustment for the conventional risk factors, elevated TG and reduced HDL-C were independently associated with impaired eGFR outcomes, whereas TC and LDL-C levels were positively associated with the eGFR. Moreover, the effects of a lower HDL-C on eGFR reduction were significantly stronger in males, those with smoking or alcohol intake habits, and overweight/obese individuals, while males were more susceptible to the effect of increased TG on the risk for a moderately/severely impaired eGFR. These findings emphasize the importance of effective control of TG and HDL-C levels for protecting renal function in Chinese adults aged 20 years and above, and the need for the development of a personalized management strategy for the at-risk population. In this respect, individuals with abnormal TG or HDL-C levels require close monitoring of the eGFR and should receive effective interventions to reduce TG and increase HDL-C.