With the high prevalence of overweight and obesity, unhealthy dietary habits and sedentary lifestyles, IFG and diabetes is increasingly common among community residents, and has become an important public health issue [37–38]. The International Diabetes Federation has predicted that the number of individuals with diabetes will increase to 380 million in 2025 and 439 million in 2030 [39–40]. The prevalence of diabetes and IFG was 14.33% and 9.37% in this population- based survey, with other studies reported in China, the prevalence of diabetes was as high as 30.6% in Heilongjiang and 17.9% in Jilin, whereas in some provinces the prevalence was as low as 3.6% in Yunnan and 5.9% in Zhejiang and 12.5% in Hunan . Participants living in Jilin and Liaoning Province showed a relatively high prevalence (11.8% and 16.5%, respectively) of IFG compared to our study [42–43], we found that the prevalence in the whole country is imbalance in geographic areas, with a vast territory, China has a tremendous difference among different regions, the levels of economic development and lifestyles differences may influence the epidemic of IFG and diabetes.
In most population-based studies, BMI, WC, WHtR are the most common obesity indexes, but there are some limitations in using these indicators to diagnose obesity. Firstly, BMI has inherent inability to distinguish subcutaneous fat and visceral fat. Secondly, BMI does not characterize body fat distribution, which was known as a determinant metabolic risk, in this aspect, WC and WHtR might better represent visceral fat. Finally, although WC and WHtR can represent central obesity, they can not show the excess body fat in circulating blood. However, a new obesity index that can predict body fat simply and effectively is urgently needed. After the first introduce by Kahn  showed that LAP is an index of excessive lipid accumulation and perform better than BMI for recognizing diabetes risk, several studies revealed the association between LAP and cardiovascular risk over the past years [44–45]. LAP, a combination of WC and TG, can reflect visceral fat excess and has theoretical basis to evaluate visceral obesity . In our study, we analyzed data from a community health management project, tried to investigate the relationship between LAP and IFG, diabetes, and compared LAP with BMI, WC, WHtR for diabetes diagnostic accuracy. The prevalence of IFG and diabetes gradually increased across LAP quartiles, the values in the fourth quartile of LAP were dramatically higher than in the first quartile (12.6% vs. 5.9%, 20.8% vs. 8.9%, respectively), and this conclusion was consistent with other similar studies in China. A cross-sectional study in Beijing showed that an elevated level of LAP was closely linked to an increased risk of diabetes in elderly people , and a survey in Anhui province confirmed that there is a positive correlation between LAP and IFG .
The results showed that the AUC of LAP (0.650) for predicting IFG and diabetes was higher than that of BMI (0.579), WHtR (0.537) and WC (0.508), indicating that LAP had more power for predicting IFG and diabetes compared with common obesity indexes. In addition, the identified cutoff value of LAP was 33.54 (sensitivity, 54.6%; specificity, 62.42%) in study population, a number of studies have found similar results. A study in northeastern Brail showed that the cutoff value of LAP index to present a higher chance of cardiovascular risk was 37.9 , an investigation conducted among Urumqi in China found that LAP was better than BMI to predict cardiovascular risk and the predictive accuracy was 38.41 in 215,651 adults . Meanwhile, in southern Taiwan, China, Chiang et al  evaluated that the optimal cutoff value for the LAP index to predict diabetes was 28.4. There is still controversy about the optimal cutoff value of LAP to present cardiovascular risk, further studies with a large sample size stratified into age, sex and nutritional status categories (obesity or normal) are needed to investigate.
The interaction analysis in this study indicated that there was a significant interaction between LAP and family history of diabetes on the risk of IFG and diabetes, the etiology of diabetes is not well defined, but family history of diabetes has been considered a reflection of both genetic and environmental effects , and individuals with family history of diabetes are two to three times more likely to develop diabetes than those without family history individuals . Similar reports reported the significant correlation between family history and risk of diabetes and IFG, a cross-sectional study in Sweden showed that family history of diabetes had an interactive influence on IFG in females . An investigation conducted by Ustulin et al  proved a relevant significant association between family history of diabetes and risk of diabetes in middle-aged and elderly person. However, no significant interaction between LAP and general obesity was observed in study population. Previous studies have explored the interaction effect between LAP and abdominal obesity on risk of diabetes [48, 55], but our result seem to be inconsistent. The results of RERI, AP indicated a significant interaction of LAP and abdominal obesity, but the result of SI did not. Abdominal obesity may result in increased blood glucose through some unknown mechanisms. So far, there are few surveys exploring the interaction of risk factors on IFG and diabetes risk, and the interactive mechanisms between LAP and other factors needs to be studied in the future.
There are some limitations in our study. First, as a cross-sectional study, the causal association between LAP and IFG, diabetes can not be determined. Secondly, we did not identify different cutoff values for LAP according to sex, age and nutritional status categories. Thirdly, the population of our study can not fully represent the general population in the center of China. Finally, the enrolled individuals in this study were all middle-aged and elderly. So we suggest that additional longitudinal studies should evaluate in different sex and age groups, given that the association between LAP and IFG, diabetes risk is well-established.