syndrome trait OR (95% CI) OR (95% CI) ORf(95%CI)
Central obesity 1.82(1.36-2.43) 1.55(1.15-2.10) 1.17(0.85-1.61)
Elevated TGs 1.73(1.32-2.26) 1.79'(1.36-2.35) 1.45(1.07-1.95)
Elevated BP 2.56(1.89-3.46) 2.03(1.49-2.77) 1.78(1.29-2.44)
ReducedHDL-C 1.38(1.04-1.83) 1.33(0.99-1.79) 1.05(0.77-1.43)
IncreasedFBG 2.55 (1.95-3.35) 2.28(1.73-3.01) 2.05(1.55-2.72)
*BP = blood pressure; CI = confidence interval; FBG = fasting blood glucose; HDL-C = high-density lipoprotein cholesterol; TGs = triglycerides. fAdjusted for age, sex, and other metabolic syndrome traits.
than 6000 subjects representative of the general US population. They discovered a significant correlation between the number of metabolic syndrome traits and albuminuria and an eGFR of less than 60 mL/min per 1.73 m2, suggesting that metabolic syndrome might be an important factor in causing CKD." To illustrate the relationship between metabolic syndrome and CKD, Kurella et al5 analyzed a cohort dataset from the Atherosclerosis Risk in Communities study. Even after adjusting for diabetes status and BP control, they found an independent association between metabolic syndrome and an increased risk of incident CKD in nondiabetic adults.5 All these studies are from the United States; indeed, only 2 studies on this topic have been conducted in Asia and none in developing countries. A study by Tanaka et al'- indicated that metabolic syndrome, defined using the criteria of the Adult Treatment Panel III, is a significant determinant of CKD, defined as an eGFR of less than 60 mL/min per 1.73 m2 or dipstick proteinuria (sl+), in a population of men aged 60 years or younger from Okinawa, Japan. Ninomiya et al" reported that metabolic syndrome was a significant risk factor for CKD in 1440 community-dwelling individuals aged 40 years or older in Japan. Although Japan is an industrialized country, its lifestyle might differ from that of China.
The current study adopted the new IDF definition of metabolic syndrome, which uses ethnic-specific values for waist circumference to define central obesity. Furthermore, we evaluated albuminuria by immunoturbidimetic methods and calculated eGFR using an equation more suitable to a Chinese population,, one that underestimated the glomerular filtration rate in stage 1 to stage 2 CKD significantly less than had previous equations. Our study revealed a graded relationship between the number of metabolic syndrome traits and the prevalence of CKD. After adjustments for age, sex. and other risk factors of CKD were made, participants with metabolic syndrome were 74% more likely to have CKD than those who did not have the syndrome. Furthermore, a strong association between metabolic syndrome and CKD was noted in subjects without hypertension and diabetes.
Epidemiological studies have documented that diabetes and hypertension are the major factors associated with the development and progression of CKD.17‑20 The results from our study of a Chinese population aged 40 years and older are consistent with those from Western countries, suggesting that even mildly elevated BP (>130/>85 mm Hg) or mildly increased FBG levels (>5.6 mmol/L) are associated with an increased risk for CKD. We also found an association between elevated TG levels and CKD, with an OR less than that for the association between CKD and elevated BP and increased FBG levels. A few epidemiological studies have found a relationship between elevated TG levels and an increased risk of CKD. A detailed lipoprotein analysis in 44 patients showed a strong correlation between a declining glomerular filtration rate and increases in the plasma concentration of TG-rich apoB-containing lipoproteins.21 In a prospective study of 12,728 subjects, high TG and low HDL cholesterol levels, but not low-density lipoprotein cholesterol levels, were shown to predict a risk for increased SCr.22 A meta-analysis indicated that 3-hydroxy-3-methylglutaryl coenzyme A reductase inhibitors (statins) may slow the progression of CKD.23 Although these studies suggest an independent role for dyslipidemia in the link between metabolic syndrome and CKD, the mechanisms whereby lipids contribute to renal injury are incompletely understood.
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Our study has some limitations. Its cross-sectional design makes it difficult to infer causality between metabolic syndrome and risk of albuminuria or reduced renal function. Furthermore, because our study population was not randomly selected from the general population, the possibility for bias exists. For example, those with diabetes/ hypertension and metabolic syndrome might have multiple morbidities and so be less likely to respond. Finally, we used an equation developed by tailoring the Modification of Diet in Renal Disease equation to data for Chinese patients with CKD9; however, a recent study by Rule et al24 showed that equations developed to estimate glomerular filtration rates in nephrology referral samples were limited in their usefulness as CKD screening tools for the general population.
Our study is important in that it shows that the link noted between metabolic syndrome and CKD in US studies was also observed in an Asian population from a densely populated developing country. According to the 1999 Chinese Dialysis and Transplantation Registration Report,4 the major cause of end-stage renal disease in Chinese adults was glomerulonephritis. However, in the past 20 years, the prevalence of diabetes and hypertension in adults has increased rapidly in China.25"27 Thus, the association between metabolic disease and CKD must be understood if the increasing use of renal replacement therapy in China is to be controlled.3-4 The findings of our study point to the urgent necessity for further research into the mechanisms of kidney damage in metabolic syndrome and for clinical trials assessing the impact of treatment for metabolic syndrome on CKD incidence and disease progression in China. Furthermore. China and other economically developing countries have experienced a cardiovascular epidemic in recent decades,28 with cardiovascular morbidity and mortality predicted to increase yet further in China.28 Both metabolic syndrome and CKD increase the risk of cardiovascular disease.29"33 Thus, effective interventions to control metabolic syndrome and CKD would help to ease the burden of chronic disease on China's limited health care resources.
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CONCLUSION
To our knowledge, this is the first report to establish a relationship between metabolic syndrome and CKD in a population from a developing country. In our study of a Chinese population (age a40 years), metabolic syndrome was associated with CKD. Further studies are needed to determine if treatment of metabolic syndrome could substantially ease the burden of CKD in China.
We thank the Department of Clinical Laboratory, Peking University First Hospital, for performing tests of albuminuria ami for calibrating serum SCr levels.
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