In this population-based study, we observed a significant increase in the odds of T2DM with the rise in LAP levels in the adult population of western Iran. Specifically, in the second to fourth quartiles of LAP levels, the odds of T2DM was 1.60, 2.43, and 3.36 times higher than in the first quartile, respectively.
The association between LAP and T2DM has been found to be positive in several demographic and ethnic subgroups. Briefly, in the Japanese population, high LAP have been shown to increase the risk of T2DM by 76% over time [20]. Similar results have been reported in adults Chinese and middle-aged Koreans [27, 28]. Studies have shown that obesity is a risk factor for T2DM [29]. The excessive accumulation of lipids or liver fat leads to a series of complex metabolic consequences, such as non-alcoholic fatty liver disease (NAFLD) and insulin resistance (IR), which ultimately contribute to the development and progression of T2DM [11, 12, 30]. Additionally, WC, relative to BMI, is a more accurate indicator for assessing excess visceral fat in the body. WC does not clearly distinguish between subcutaneous and visceral fat in the abdominal cavity [30]. Furthermore, dyslipidemia, hypertriglyceridemia, and low HDL cholesterol levels have been observed to be related to T2DM [31]. Therefore, LAP, as a composite index of WC and TG, reflects the state of visceral fat and blood lipids. A strong relationship between LAP and metabolic diseases such as CVD and hypertension has also been observed [19, 32]. Generally, the positive relationship between LAP and diabetes is acceptable.
In individuals who are overweight, excessive fat tissue in the body, combined with overeating and chronic inflammation, can result in IR and a disorder in glucose metabolism [33]. IR is a crucial stage in the progression of diabetes [34], and chronic inflammation and mitochondrial dysfunction caused by obesity can both worsen IR [35–37]. Additionally, prolonged exposure to fatty acids in β-cells can decrease glucose-induced insulin secretion, disrupt insulin gene expression, and increase cell death [38, 39]. The onset of T2DM is gradual and may lead to complications for an individual before it is diagnosed, making early diagnosis and prevention particularly important. Considering the change in lifestyle and the increasing trend of T2DM as well as serious complications, reduction in quality of life and heavy economic burden caused by this disease, it is very important to provide a low-cost, easy and calculable index to identify T2DM as soon as possible. Previous studies have shown that LAP has a higher diagnostic value for predicting T2DM than indicators such as BMI, WC, A Body Shape Index (ABSI), Visceral adiposity index (VAI) and waist/height ratio (WHtR) [20, 40]. Similarly, the present study also showed that LAP (AUC = 0.66) has higher diagnostic value than WC (AUC = 0.60) and TG (AUC = 0.64). Furthermore, LAP has been identified as a useful indicator for predicting metabolic diseases like hypertension and CVD [18, 19]. Based on the results of this study in a population of 9,065 participants including men and women and residents of cities and villages, and the results of previous studies, we suggest LAP as an accurate and comprehensive index for T2DM screening in large populations.
The study had a few limitations. It was a cross-sectional analysis, which means that the observed relationships are not causal. However, causal relationships in longitudinal studies have been observed in other population groups. Additionally, the study was conducted on adults in western Iran, so the results should be cautiously generalized to other population groups. It is recommended to carry out this study in other population subgroups. Lastly, the study did not measure HbA1c and oral glucose tolerance test variables. The large sample size is a key advantage of the current study. Additionally, the comprehensive collection of lifestyle, anthropometric, and biochemical variables, as well as the adjustment of a large number of confounding variables, is strength of this study.