2025 Volume 72 Issue 1 Pages 43-51
Non-high-density lipoprotein cholesterol (non-HDL), a more readily available and reliable lipid parameter, is unclear in its association with type 2 diabetes (T2D). Previous studies assessing the relationship between non-HDL and T2D risk remains inconsistent results. We performed a meta-analysis to systematically evaluate this association. The PubMed, EMBASE, Medline, Web of Science, and Cochrane Library databases were systematically searched to find articles on “non-HDL” and “T2D” from inception to December 6, 2023. A random-effects model was used to calculate the effect estimates and 95% confidence intervals. Subgroup analyses and univariate Meta-regression were performed to explore sources of heterogeneity. The main exposure and outcome were non-HDL and T2D, respectively, in the general population. A total of 8 studies included 251,672 participants who met the inclusion criteria for this study. Meta-analysis showed that higher non-HDL increased the risk of T2D compared with the lower non-HDL group (total effect size: 1.16; 95% CI 1.079–1.251, p < 0.001). Subgroup analyses and Meta-regression of the association between non-HDL and T2D were not affected by region, proportion of men, sample size, or adjustment for confounders (including BMI, hypertension, waist circumference, and family history of diabetes). Higher non-HDL may be associated with an increased risk of T2D. Large prospective cohort studies are needed to validate these findings, and further studies are required in order to elucidate the underlying pathophysiologic mechanisms underlying the association between non-HDL and T2D.
Type 2 diabetes (T2D) is a prevalent and serious chronic condition influenced by intricate genetic-environmental interplays, alongside factors such as unhealthy dietary patterns and sedentary lifestyles [1, 2]. T2D comprises approximately 90 percent of the 537 million global diabetes cases, with its incidence continuing to rise. Projections suggest that by 2045, T2D may afflict around 783 million individuals worldwide [3]. Presently, roughly 80% of T2D occurrences arise in low- and middle-income nations [4]. In China, diabetes prevalence escalated from 9.7 percent in 2008 to 11.2 percent in 2017, positioning China as the nation with the highest T2D patient population globally [5]. Disruptions in glucolipid metabolism significantly jeopardize cardiovascular health, predisposing individuals to organ malfunction and premature mortality [6]. Dyslipidemia is a prevalent feature of insulin resistance and T2D, constituting a critical risk factor for abnormal glucose regulation [7]. Studies indicate that approximately 75% of diabetic patients exhibit abnormal lipid metabolism. Dysfunctions in lipid metabolism are pivotal in diabetes pathogenesis [8]. Fatty acids can induce insulin resistance in peripheral tissues and disrupt pancreatic islet β-cell function, thereby promoting diabetes onset [8, 9].
Non-high-density lipoprotein cholesterol (non-HDL) encompasses all cholesterol content within potentially atherogenic lipoprotein particles, including low-density lipoprotein cholesterol (LDL-C), lipoprotein (a), very-low-density lipoprotein cholesterol (VLDL-C), VLDL remnant, and intermediate-density lipoprotein (IDL-C) [10]. Non-HDL is recognized as a more practical and reliable predictor of coronary artery disease (CAD), a fact corroborated by numerous epidemiological investigations and clinical trials [11]. A study conducted by Vega et al. showed a 20.9% decrease in non-HDL-C levels in free-living subjects with diabetes mellitus but without arteriosclerotic cardiovascular disease (ASCVD) from the NHANES survey conducted between 1999 and 2016 [12]. Another study showed that non-HDL-C levels were positively associated with pre-diabetes and diabetes status in patients [13].
A mounting body of research suggests that elevated levels of non-HDL are correlated with an increased risk of type 2 diabetes (T2D) within the general population. However, evidence from observational studies presents inconsistent findings regarding the association between non-HDL and T2D risk [14-21]. Given the contentious nature of non-HDL’s role in T2D risk, its relationship has yet to be conclusively established through meta-analyses. Therefore, our present systematic review and meta-analysis aim to synthesize and pool available data to investigate the link between non-HDL and T2D, potentially furnishing a more scientifically grounded basis for enhanced T2D prevention and management strategies.
The current study adhered to the guidelines outlined in the Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) (Supplementary Table 1). Furthermore, this study was registered with the International Prospective Register of Systematic Reviews (PROSPERO) under the registration number CRD42024499526.
Search strategyWe systematically searched multiple electronic databases, including PubMed, EMBASE, Medline, Web of Science, and the Cochrane Library, from inception until December 2023 to identify relevant studies (Supplementary Table 2). The search terms, connected by Boolean logical operators “OR” or “AND,” encompassed: (1) non-HDL-C, non-HDL cholesterol, non-HDL-cholesterol, non-HDL-cholesterol, non-HDL-cholesterol, non-HDL-cholesterol, non-HDL-cholesterol, and non-HDL-cholesterol, cholesterol, non-high-density lipoprotein cholesterol, non-HDL; (2) type 2 Diabetes Mellitus, type 2 Diabetes, T2D, Diabetes Mellitus Type II, type II Diabetes Mellitus, Diabetes Type II. Two investigators independently conducted a systematic search of all relevant references. There were no additional restrictions regarding time, country, or language. Furthermore, we analyzed the reference lists of relevant original articles and review articles.
Study selectionTwo evaluators will independently screen titles and abstracts to identify potentially eligible studies based on the inclusion criteria. Inclusion criteria included the following: (1) cohort studies published in full text; (2) examination of the association between non-HDL levels and the risk of T2D; (3) reporting of the association between non-HDL and the risk of T2D in terms of odds ratios (ORs) or hazard ratios (HRs) with their 95% confidence intervals (CIs). Exclusion criteria consist of: (1) conference proceedings; (2) experimental and interventional studies, reviews, and case reports; (3) studies with incomplete information; (4) studies not published in English.
Data extraction and quality assessmentTwo investigators independently extracted information from the literature based on predefined inclusion criteria. The extracted data included: (1) the name of the first author, year of publication, and country where the study was conducted; (2) characteristics of the study design; (3) participant characteristics, such as study population, sample size, age, and gender; (4) duration of study follow-up; (5) definition and diagnosis of outcome; (6) confounders adjusted for in multivariate analyses; (7) adjusted risk estimates (OR or HR values) and their 95% confidence intervals. Two researchers critically reviewed all relevant studies, extracted potentially eligible data, and thoroughly resolved any uncertainties or discrepancies. The quality of cohort studies was assessed using the Newcastle-Ottawa Scale (NOS), which ranges from 0 to 9. Studies with a NOS score of ≥6 were deemed to have a low risk of bias [22].
Statistical analysisSystematic evaluation and meta-analysis were performed using Stata 14.0 software. The multivariate-adjusted risk estimates (OR or HR values) and their 95% confidence intervals (CIs) were collected from all individual studies. Statistical heterogeneity was analyzed using Cochran’s Q statistic and I2 statistic [23]. An indicator of significant heterogeneity was considered if I2 was greater than 75%. Then the analysis was conducted using the random effects model. Subgroup analysis was used to explore the heterogeneity of included studies and meta-regression analysis was conducted to test for the source of heterogeneity among subgroups [24]. Sensitivity analysis was used to further test the impact of individual studies on the overall results and to analyze whether the results were robust and reliable [25]. The presence of potential publication bias was assessed by funnel plot, Begg’s test, and Egger’s test [26]. The trim and fill method was utilized to correct for biased results and to assess the impact of bias on the combined risk estimate [27].
A total of 5,218 articles were identified through searches conducted in PubMed, EMBASE, Medline, Web of Science, and the Cochrane Library databases. Among these articles, 358 studies were excluded due to duplication or irrelevant topics. Subsequently, after reviewing titles and abstracts, 4,795 articles were excluded. Upon full-text examination, 57 records were further excluded. Ultimately, only 8 studies met our selection criteria and were included in the quantitative assessment of the meta-analysis (Fig. 1).
We included eight cohort studies conducted in China, Korea, Canada, and Iran, published between 2011 and 2022. The total participant count across these studies was 251,672, comprising 34,382 patients with T2D and 217,290 patients without T2D. Four studies were conducted in Korea, two in Iran, one in China, and one in Canada. The study with the largest sample size, conducted by You-Cheol Hwang et al. in Korea, included 118,429 participants, while the study with the smallest sample size, by Ley et al., included 492 participants. Primary data sources included the Korean Genome and Epidemiology Study (KoGES), the Tehran Lipid and Glucose Study (TLGS), the Isfahan Diabetes Prevention Study, and hospital or community-based population studies. Baseline characteristics, such as study source, sample size, and other relevant details, were summarized in Table 1. Newcastle-Ottawa Scale (NOS) assessment revealed that two studies achieved a NOS score of 9, three studies scored 8, and three studies scored 7 (Supplementary Table 3).
Study | Country | Design | Study population | Male% | Mean age | Study time | Non-HDL analysis | Definition and diagnosis of outcome | Variables adjusted |
---|---|---|---|---|---|---|---|---|---|
S. H. Ley [14] | Canada | cohort | 492 participants without diabetes | 42.1% | NA | 10-year | continuous | Incidence of T2D was defined as: fasting plasma glucose ≥7.0 mmol/L or 2h postload glucose ≥11.1 mmol/L on a 2h-OGTT; current use of insulin or oral hypoglycaemic agents; a positive response to the question: Have you ever been diagnosed with diabetes by a nurse or doctor? | age, sex, hypertension, ever smoking and log C-reactive protein, waist circumference |
Mi Hae Seo [15] | Korea | retrospective, longitudinal | 5,577 participants without diabetes | 70.3% | 44.5 | 4-year | continuous | Incidence of T2D was defined as: fasting plasma glucose 126 mg/dL or greater; or a HbA1c 6.5% or greater; subjects who had a history of diabetes or currently used insulin or oral antidiabetic drugs based on a self-report questionnaire at each visit | age and gender, BMI, smoking status, hypertension, fasting glucose, fasting insulin |
You-Cheol Hwang [16] | Korea | retrospective longitudinal | 84,394 participants without diabetes | 57.9% | 38.4 | 3.3-year | continuous | Incidence of T2D was defined as: fasting glucose levels 126 mg/dL (7.0 mmol/L); taking oral hypoglycemic agents or insulin therapy; a self-reported history of diabetes; HbA1c levels ≥6.5% | Age, sex, waist circumference, fasting serum insulin, TG, HDL-C, family history of diabetes, and systolic blood pressure |
Erfan Sadeghi [17] | Iran | follow-up | 1,222 participants without diabetes | 26.8% | 42.9 | 14-year | continuous | Incidence of T2D was defined as: FPG ≥126 mg/dL; 2h plasma glucose ≥200 mg/dL; HbA1c ≥6.5% | NA |
Pegah Khaloo [18] | Iran | prospective | 5,474 participants without diabetes | 42.4% | 41.3 | 8.9-year | continuous | Incidence of T2D was considered to be present: using antidiabetic drugs; FPG was ≥7 mmol/L or if the 2h-PLG was ≥11.1 mmol/L | age sex, education, lipid drug use, family history of T2DM, history of cardiovascular disease, hypertension and baseline measurements of FPG, BMI, waist circumferences and lipid profile, BMI change, FPG change |
In-Ho Seo [19] | Korea | prospective cohort | 7,608 participants without diabetes | 46.9% | 51.7 | 14-year | Q4:Q1 | Incidence of T2D was defined as: FPG ≥126 mg/dL; a plasma glucose level ≥200 mg/dL at two hours after a 75-g OGTT; an HbA1c ≥6.5%; or current treatment with oral anti-diabetic medications or insulin therapy | age, sex, waist circumference, smoking status, alcohol intake, physical activity, mean arterial blood pressure, family history of diabetes and HOMA-IR |
Tong Yang [20] | China | retrospective cohort | 28,476 CHD participants without diabetes | 44.07% | 64 | 6.75-year | continuous | Incidence of T2D was defined as: FBG ≥7.0 mmol/L; HbA1c ≥6.5% | age, sex, SBP, smoking, hypertension, family history of T2DM, current antilipidemic medication, current antihypertensive medication |
Y.-C. Hwang [21] | Korea | longitudinal | 118,429 participants without diabetes | 59.9% | 39.6 | 3.1-year | continuous | Incidence of T2D was defined as: fasting glucose levels ≥7.0 mmol/L; taking oral hypoglycaemic agents or insulin therapy; a self-reported history of diabetes; HbA1c levels ≥48 mmol/mol (6.5%) | age and sex waist circumference, FPG, fasting serum insulin, HbA1c, family history of diabetes and SBP, TG and HDL-C |
BMI, body mass index; OGTT, oral glucose tolerance test; HbA1c, Hemoglobin A1C; FPG, fasting plasma glucose; FBG, fasting blood glucose; Q4:Q1, the 4th quintile vs. The 1st quintile; TG, triglyceride; HDL-C, high-density lipoprotein cholesterol; SBP, systolic blood pressure; PLG, postload glucose; HOMA-IR, homeostatic model assessment for insulin resistance; NA, not applicable; CHD, coronary heart disease.
This meta-analysis, comprising eight studies [14-21], indicates that elevated non-HDL levels are associated with an increased risk of developing T2D compared to the general population with a lower non-HDL levels (pooled effect size 1.16, 95% CI 1.079–1.251) (Fig. 2). However, significant heterogeneity was observed in the analysis (I2 = 97.3%, p < 0.001).
The sensitivity analysis revealed no extreme results affecting the pooled estimates (Supplementary Fig. 1 and Supplementary Table 4). Furthermore, subgroup analyses were conducted by region, sample size, and proportion of males (Table 2). Within the subgroup analyses by region, both Asia (effect size: 1.15, 95% CI: 1.06–1.24) and North America (effect size: 1.43, 95% CI: 1.078–1.897) yielded consistent results. Moreover, subgroup analyses based on sample sizes indicated that non-HDL were associated with T2D (sample size >8,000 [effect size: 1.146, 95% CI: 1.128–1.165], sample size ≤8,000 [effect size: 1.203, 95% CI: 1.036–1.397]). Subgroup analyses concerning the proportion of male participants exhibited consistent associations for male proportions >50% [effect size: 1.142, 95% CI: 1.113–1.172] and male proportions ≤50% [effect size: 1.166, 95% CI: 1.047–1.299]. Additionally, given that BMI, waist circumference, hypertension, and family history of diabetes are also recognized risk factors for T2D, stratified subgroup analyses were conducted based on whether these variables were adjusted in the included studies. The results remained consistent with the pooled effect size.
Analysis | Number of studies | Effect Size (95%CI) | p (Z-test) | I2(%) | p (Q-test) |
---|---|---|---|---|---|
Region | |||||
Asia | 7 | 1.150 (1.066–1.240) | <0.001 | 97.6% | <0.001 |
North America | 1 | 1.430 (1.078–1.897) | 0.013 | — | — |
Sample size | |||||
>8,000 | 3 | 1.146 (1.128–1.165) | <0.001 | 91% | 0.375 |
≤8,000 | 5 | 1.203 (1.036–1.397) | 0.015 | 0% | <0.001 |
Male% | |||||
>50% | 3 | 1.142 (1.113–1.172) | 0.005 | 21.2% | 0.281 |
≤50% | 5 | 1.166 (1.047–1.299) | <0.001 | 97.2% | <0.001 |
Adjustment for hypertension | |||||
Yes | 4 | 1.160 (1.067–1.261) | <0.001 | 63.8% | 0.040 |
No | 4 | 1.155 (1.048–1.273) | 0.004 | 97.9% | <0.001 |
Adjustment for waist circumference | |||||
Yes | 5 | 1.171 (1.096–1.251) | 0.065 | 80.3% | <0.001 |
No | 3 | 1.121 (0.993–1.267) | <0.001 | 98.3% | <0.001 |
Adjustment for family history of diabetes | |||||
Yes | 5 | 1.153 (1.105–1.203) | <0.001 | 79% | <0.001 |
No | 3 | 1.177 (0.961–1.442) | 0.115 | 88% | 0.001 |
Adjustment for BMI | |||||
Yes | 2 | 1.133 (0.949–1.352) | 0.168 | 79.8% | 0.026 |
No | 6 | 1.172 (1.077–1.276) | <0.001 | 98% | <0.001 |
The results of univariate meta-regression analyses revealed that the incorporation of studies based on region, study design, sample size, the proportion of males, and various adjustment factors such as BMI, hypertension, family history of diabetes, and waist circumference did not significantly influence the association between non-HDL cholesterol and T2D (all p-values >0.10) (Table 3). These findings imply that disparities in these characteristics may not serve as major contributors to heterogeneity. The Begg’s test and Egger’s test indicated potential publication bias (p = 0.536 and p = 0.020, respectively). The funnel plot illustrated that some studies tended to skew towards the right side of the funnel (Supplementary Fig. 2). Subsequently, the trim and fill method was conducted, revealing no significant change in the effect size (adjusted pooled estimate: 1.130, 95% CI: [1.052, 1.213], p = 0.001), suggesting that publication bias had little effect on the results.
Variables | Coefficient (95%CI) | SE | p |
---|---|---|---|
Region | 0.208 (–0.278,0.707) | 0.203 | 0.328 |
Male% | 0.005 (–0.252,0.263) | 0.105 | 0.958 |
Sample size | 0.041 (–0.211,0.294) | 0.103 | 0.703 |
Adjustment for BMI | 0.045 (–0.245,0.336) | 0.118 | 0.714 |
Adjustment for waist circumference | –0.070 (–0.316,0.176) | 0.101 | 0.511 |
Adjustment for hypertension | –0.011 (–0.265,0.243) | 0.103 | 0.919 |
Adjustment for family history of diabetes | –0.012 (–0.281,0.256) | 0.109 | 0.914 |
In this meta-analysis of cohort studies, we found that compared to the general population with a lower group of non-HDL, higher non-HDL was more likely to increase the risk of T2D. Furthermore, the association between non-HDL and T2D remained consistent in subgroup analyses according to the study design, region, proportion of males, sample size, and adjustment for several confounding factors such as BMI, hypertension, waist circumference, and family history of diabetes.
Multiple studies suggest that non-HDL cholesterol serves as a superior indicator of cardiovascular disease progression in comparison to conventional lipid parameters. While conventional lipid parameters, including LDL cholesterol, are well-established markers associated with incident T2D, limited evidence exists regarding the association between non-HDL cholesterol and incident T2D. Higher non-HDL cholesterol signifies the presence of remnants of atherogenic lipoproteins, which promote the development of small, dense low-density lipoprotein cholesterol particles in individuals with insulin resistance, metabolic syndrome, obesity, and diabetes [28]. Recent guidelines propose that non-HDL cholesterol stands as a more robust independent risk factor for cardiovascular disease and should be regarded as a risk marker and secondary therapeutic target for cardiovascular disease management [29]. While the precise mechanism by which non-HDL impacts T2D remains unclear, several potential mechanisms have been proposed. Aberrations in lipid levels may precipitate insulin resistance and atherosclerosis, which are pivotal contributors to diabetes [30-32]. Within this cascade, the vasoactive hormonal pathway, particularly the renin-angiotensin-aldosterone system (RAAS), assumes significance as a crucial system for regulating plasma sodium concentration, arterial blood pressure, and extracellular volume [33]. An imbalance between renin and angiotensin II may instigate various chronic and acute diseases [34], with early plaque formation induced by angiotensin II standing out as a key function of RAAS in atherosclerosis [35]. In pathological contexts, the RAAS also contributes, either directly or indirectly, to the progression of atherosclerosis and its diverse complications through its interactions with other systems [36]. Moreover, an imbalance between renin and angiotensin II within the detrimental axis of RAAS amplifies the release of inflammatory cytokines and fosters oxidative stress [37]. These pathological alterations further stimulate atherosclerosis formation, exacerbate insulin resistance, and diminish insulin secretion, thereby fostering the onset and progression of diabetes mellitus.
Given the significant heterogeneity of this study, we used subgroup analysis and meta-regression to probe into sources of heterogeneity. Due to the restricted number of included studies, subgroup analyses were performed based on a few methodological and clinical characteristics. The analysis of eight cohort studies indicated that elevated non-HDL levels were linked to an increased risk of T2D. However, caution is warranted in interpreting this finding due to the limited number of studies encompassing different study types. Subgroup analyses based on various geographical regions revealed a notable association between non-HDL and T2D in Asia and North America. Notably, our study comprised only one investigation conducted in North America, while the remaining seven studies were conducted in Asia, thereby constraining the regional diversity of our findings. While most articles have adjusted for certain risk factors for T2D, including gender, age, hypertension, smoking, alcohol consumption, body mass index, and family history of cerebrovascular disease, other potential confounding variables such as sedentary lifestyle, dietary habits, history of gestational diabetes, presence of diabetes-related end-organ damage, presence of cardiovascular risk factors, and additional T2D risk factors have not been consistently accounted for. Consequently, prospective studies with appropriate controls that comprehensively adjust for potential confounders are urgently required to further explore the association between non-HDL and T2D.
Our study highlights the significance of utilizing non-HDL as a potential indicator of T2D risk in the general population. Given its ready availability, cost-effectiveness, and routine incorporation into clinical practice, non-HDL emerges as a convenient tool for assessing T2D risk. Nonetheless, our study is not devoid of limitations. The predominantly observational nature of the included studies entails a lower level of evidence compared to randomized controlled trials. Furthermore, aside from non-HDL, residual confounders such as diet and physical activity may also exert an influence on T2D risk. The exact nature of the relationship between non-HDL and T2D risk remains uncertain due to limitations in the number of studies. Moreover, the wide variation in sample sizes across the included studies may introduce unforeseen effects on the findings. Therefore, further large-scale cohort studies and foundational investigations are imperative to procure more definitive evidence.
In summary, the findings of our meta-analysis suggest a plausible association between elevated non-HDL levels and heightened risk of incidence of T2D. More prospective cohort studies and fundamental investigations are indispensable. Also, further studies are needed to elucidate the underlying mechanisms between non-HDL and T2D.
MQH performed the literature search and drafted the manuscript. YS and CH screened the literature. XG and XCJ extracted data and assessed the quality. HYG analyzed and interpreted the data. YLJ and HY reviewed the manuscript. All authors listed have made a substantial, direct, and intellectual contribution to the work, and approved it for publication.
This study was supported by grants from Horizontal Project of Wannan Medical College (2309-510-JXKY).
The study does not involve ethical approval and consent.
The authors declare that they have no conflict of interest.
Not applicable.
We’d like to thank all the authors who participated in the article.