Date Published: August 28, 2018
Publisher: Public Library of Science
Author(s): QiPing Feng, Wei-Qi Wei, Cecilia P. Chung, Rebecca T. Levinson, Alexandra C. Sundermann, Jonathan D. Mosley, Lisa Bastarache, Jane F. Ferguson, Nancy J. Cox, Dan M. Roden, Joshua C. Denny, MacRae F. Linton, Digna R. Velez Edwards, C. Michael Stein, Sanjay Basu
Abstract: BackgroundObservations from statin clinical trials and from Mendelian randomization studies suggest that low low-density lipoprotein cholesterol (LDL-C) concentrations may be associated with increased risk of type 2 diabetes mellitus (T2DM). Despite the findings from statin clinical trials and genetic studies, there is little direct evidence implicating low LDL-C concentrations in increased risk of T2DM.Methods and findingsWe used de-identified electronic health records (EHRs) at Vanderbilt University Medical Center to compare the risk of T2DM in a cross-sectional study among individuals with very low (≤60 mg/dl, N = 8,943) and normal (90–130 mg/dl, N = 71,343) LDL-C levels calculated using the Friedewald formula. LDL-C levels associated with statin use, hospitalization, or a serum albumin level < 3 g/dl were excluded. We used a 2-phase approach: in 1/3 of the sample (discovery) we used T2DM phenome-wide association study codes (phecodes) to identify cases and controls, and in the remaining 2/3 (validation) we identified T2DM cases and controls using a validated algorithm. The analysis plan for the validation phase was constructed at the time of the design of that component of the study. The prevalence of T2DM in the very low and normal LDL-C groups was compared using logistic regression with adjustment for age, race, sex, body mass index (BMI), high-density lipoprotein cholesterol, triglycerides, and duration of care. Secondary analyses included prespecified stratification by sex, race, BMI, and LDL-C level. In the discovery cohort, phecodes related to T2DM were significantly more frequent in the very low LDL-C group. In the validation cohort (N = 33,039 after applying the T2DM algorithm to identify cases and controls), the risk of T2DM was increased in the very low compared to normal LDL-C group (odds ratio [OR] 2.06, 95% CI 1.80–2.37; P < 2 × 10−16). The findings remained significant in sensitivity analyses. The association between low LDL-C levels and T2DM was significant in males (OR 2.43, 95% CI 2.00–2.95; P < 2 × 10−16) and females (OR 1.74, 95% CI 1.42–2.12; P = 6.88 × 10−8); in normal weight (OR 2.18, 95% CI 1.59–2.98; P = 1.1× 10−6), overweight (OR 2.17, 95% CI 1.65–2.83; P = 1.73× 10−8), and obese (OR 2.00, 95% CI 1.65–2.41; P = 8 × 10−13) categories; and in individuals with LDL-C < 40 mg/dl (OR 2.31, 95% CI 1.71–3.10; P = 3.01× 10−8) and LDL-C 40–60 mg/dl (OR 1.99, 95% CI 1.71–2.32; P < 2.0× 10−16). The association was significant in individuals of European ancestry (OR 2.67, 95% CI 2.25–3.17; P < 2 × 10−16) but not in those of African ancestry (OR 1.09, 95% CI 0.81–1.46; P = 0.56). A limitation was that we only compared groups with very low and normal LDL-C levels; also, since this was not an inception cohort, we cannot exclude the possibility of reverse causation.ConclusionsVery low LDL-C concentrations occurring in the absence of statin treatment were significantly associated with T2DM risk in a large EHR population; this increased risk was present in both sexes and all BMI categories, and in individuals of European ancestry but not of African ancestry. Longitudinal cohort studies to assess the relationship between very low LDL-C levels not associated with lipid-lowering therapy and risk of developing T2DM will be important.
Partial Text: Drugs such as HMG-CoA reductase inhibitors (statins) lower low-density lipoprotein cholesterol (LDL-C) concentrations and are effective for primary and secondary prevention of coronary artery disease [1–3]. However, statin therapy is associated with an approximately 9%–12% increase in the risk of new-onset type 2 diabetes mellitus (T2DM) [4,5]. The risk of diabetes could be increased by statins directly, and, in keeping with this possibility, the risk could be increased with higher doses ; however, genetic approaches have also implicated low LDL-C concentrations as a risk factor for T2DM.
We identified 8,943 individuals with low (≤60 mg/dl) and 71,343 individuals with normal (90–130 mg/dl) LDL-C concentrations. Compared to the normal LDL-C group, individuals with low LDL-C were younger, had lower BMI and triglycerides, and were more likely to be female and of African ancestry (Tables 1 and S2). The normal and low LDL-C groups had similar sex distribution, HDL-C levels, and length of EHR. The discovery group was composed of 2,982 individuals with low and 23,771 with normal LDL-C concentrations; the validation group had 5,961 individuals with low and 47,572 with normal LDL-C (Fig 1).
The major new finding of the study is that low LDL-C concentrations occurring independently of statin treatment were associated with a 2-fold increased risk of T2DM.