Vitamin D plays an important role in maintaining the integrity of bone. It contributes to the growth and development of bone in children and maintains the bone health in adults. Furthermore, vitamin D helps to prevent osteoporosis and fracture in the elderly [
314 patients (196 males and 118 females) with T2DM who were hospitalized in the Department of Endocrinology of the First Affiliated Hospital of Zhengzhou University from September 2015 to February 2016 were enrolled. The diagnosis of the T2DM corresponds to the diagnostic criteria made by the Word Health Organization (WHO) in 1999. The exclusion criteria are as follows: patients with acute diabetic complications such as acute infection, ketoacidosis, and hyperosmolar coma; serious liver and kidney dysfunction; thyroid, parathyroid, and other endocrine gland-related diseases; autoimmune diseases; osteoporosis and other bone metabolic diseases; tumor; pregnant women; mental disease; recent surgery; taking any medications known to affect vitamin D metabolism; and patients with a recent history of excess ultraviolet (UV) ray exposure.
This study complied with the principles of the Declaration of Helsinki and was approved by the local ethics committee. Written informed consent was obtained from all subjects.
General clinical data including sex, age, diabetes duration, smoking history, hypertension history, family history of diabetes, height, weight, systolic blood pressure (SBP), and diastolic blood pressure (DBP) was recorded for all patients. Body mass index (BMI) was calculated as weight in kilograms divided by height per square meter.
Blood samples were obtained by venipuncture after an overnight fast. Serum calcium, uric acid, triglyceride (TG), total cholesterol (TC), high-density lipoprotein cholesterol (HDL-C), low-density lipoprotein cholesterol (LDL-C), and other conventional biochemical indicators were measured on an automatic analyzer (Hitachi 7600-020, Japan). FBG was measured by glucose oxidase method. HbA1c was measured by an automated high-performance liquid chromatography analyzer. 25(OH)D3, parathyroid hormone (PTH), and osteocalcin (OSTE) were measured using an electrochemiluminescence immunoassay (Cobas e411 analyzer, Roche, Germany). The normal reference value of 25(OH)D3 levels in our laboratory was >18.0 ng/mL.
The Aloka-
SPSS 21.0 statistic software (SPSS for Windows 21.0) was used to analyse all the data. Continuous variables were presented as mean ± standard deviations
The range of 25(OH)D3 levels in all the subjects was (3.0–45.1) ng/mL [(14.4 ± 7.0) ng/mL, M: 13.9 ng/mL]. There were 233 patients with 25(OH)D3 levels below 18 ng/mL and 81 patients with 25(OH)D3 levels above 18 ng/mL. All the subjects were divided into four quartile groups according to the serum 25(OH)D3 levels: group Q1(<8.9 ng/mL, 71 cases); group Q2 (8.9–13.9 ng/mL, 85 cases); group Q3 (13.9–18.1 ng/mL, 77 cases); and group Q4 (≥18.1 ng/mL, 81 cases). As illustrated in Table
Baseline characteristics of type 2 diabetic patients by quartiles of serum 25(OH)D3 concentrations.
Variables | Q1 |
Q2 |
Q3 |
Q4 |
|
---|---|---|---|---|---|
|
71 | 85 | 77 | 81 | — |
Sex (M/F) | 40/31 | 51/34 | 50/27 | 55/26 | 0.462 |
Age (years) | 53.0 ± 10.5 | 53.2 ± 12.4 | 52.4 ± 12.4 | 50.9 ± 12.4 | 0.614 |
BMI (kg/m2) | 25.8 ± 3.7 | 25.3 ± 4.1 | 25.5 ± 2.9 | 25.0 ± 3.4 | 0.086 |
SBP (mmHg) | 138.8 ± 20.2 | 136.8 ± 14.3 | 131.5 ± 17.5a | 133.5 ± 18.2 | 0.052 |
DBP (mmHg) | 83.2 ± 11.4 | 85.5 ± 10.3 | 82.6 ± 8.6 | 83.0 ± 10.3 | 0.235 |
Total cholesterol (mmol/L) | 4.5 ± 1.1 | 4.4 ± 1.1 | 4.2 ± 0.9 | 4.4 ± 1.0 | 0.300 |
Triglyceride (mmol/L) | 2.2 ± 1.7 | 1.9 ± 1.8 | 1.9 ± 1.3 | 1.9 ± 1.4 | 0.485 |
HDL-C (mmol/L) | 1.1 ± 0.3 | 1.2 ± 0.4a | 1.1 ± 0.2 | 1.1 ± 0.2 | 0.064 |
LDL-C (mmol/L) | 3.0 ± 0.8 | 2.8 ± 0.9 | 2.6 ± 0.8a | 2.6 ± 0.8a | 0.028 |
Uric acid (μmol/L) | 284.6 ± 91.1 | 266.5 ± 76.8 | 284.1 ± 92.7 | 275.3 ± 80.0 | 0.484 |
Parathyroid hormone (pg/mL) | 47.8 ± 36.3 | 38.0 ± 15.0ab | 37.2 ± 12.4a | 31.3 ± 9.8a | 0.000 |
Osteocalcin (ng/mL) | 13.4 ± 5.7 | 13.9 ± 5.1 | 12.8 ± 6.1 | 13.9 ± 5.3 | 0.665 |
FBG (mmol/L) | 8.0 ± 3.4 | 7.9 ± 2.7 | 7.9 ± 2.8 | 8.7 ± 3.2 | 0.318 |
HbA1c (%) | 10.2 ± 1.2 | 10.0 ± 1.3b | 9.6 ± 1.6ab | 8.6 ± 1.4a | 0.000 |
Diabetes duration (months) | 112.5 ± 87.9 | 98.0 ± 86.6 | 84.8 ± 71.0a | 82.3 ± 75.4a | 0.085 |
Calcium (mmol/L) | 2.22 ± 0.13 | 2.31 ± 0.10a | 2.32 ± 0.10a | 2.31 ± 0.10a | 0.000 |
Carotid IMT (mm) | 1.23 ± 0.40 | 1.19 ± 0.31bc | 1.06 ± 0.22ab | 0.93 ± 0.17a | 0.000 |
Carotid plaque [ |
40 (56.3%)b | 58 (68.2%)b | 48 (62.3%)b | 32 (39.5%) | 0.002 |
Smoking history [ |
27 (38.0%) | 29 (34.1%) | 22 (28.6%) | 24 (29.6%) | 0.586 |
Family history of DM [ |
37 (52.1%) | 39 (45.9%) | 30 (39.0%) | 44 (54.3%) | 0.217 |
Hypertension history [ |
30 (42.3%) | 39 (45.9%) | 31 (40.3%) | 29 (35.8%) | 0.614 |
Data are presented as mean ± SD for continuous variables and number (percentages) for dichotomous variables. Differences were assessed by the LSD-
Carotid IMT of patients in group Q1 [(1.23 ± 0.40) mm] and group Q2 [(1.19 ± 0.31) mm] was significantly higher than that in group Q3 [(1.06 ± 0.22) mm] and group Q4 [(0.93 ± 0.17) mm], the carotid IMT in group Q3 was significantly higher than that in group Q4 (
Compared with the nonplaque group, patients in the plaque group were older, had a longer duration of diabetes, and had higher SBP, HbA1c, and LDL-C (
Comparison of clinical characteristics in type 2 diabetic patients with and without carotid plaque.
Variables | Plaque group |
Nonplaque group |
|
---|---|---|---|
Sex (M/F) | 118/60 | 78/58 | 0.126 |
Age (years) |
56.5 ± 10.8 | 47.0 ± 11.3 | 0.000 |
BMI (kg/m2) | 25.2 ± 3.4 | 25.5 ± 3.7 | 0.603 |
SBP (mmHg) | 136.8 ± 18.3 | 132.9 ± 16.7 | 0.055 |
DBP (mmHg) | 82.8 ± 9.9 | 84.6 ± 10.5 | 0.127 |
Total cholesterol |
4.4 ± 1.1 | 4.3 ± 1.0 | 0.720 |
Triglyceride (mmol/L) | 1.9 ± 1.5 | 2.0 ± 1.6 | 0.531 |
HDL-C (mmol/L) | 1.1 ± 0.3 | 1.1 ± 0.3 | 0.451 |
LDL-C (mmol/L) |
2.8 ± 0.9 | 2.6 ± 0.7 | 0.010 |
Uric acid ( |
273.7 ± 82.4 | 281.7 ± 88.3 | 0.344 |
25(OH)D3 (ng/mL) |
13.4 ± 5.8 | 15.7 ± 8.0 | 0.004 |
Parathyroid |
38.7 ± 23.1 | 37.7 ± 18.2 | 0.695 |
Osteocalcin (ng/mL) | 13.1 ± 6.1 | 14.1 ± 4.7 | 0.199 |
FBG (mmol/L) | 8.2 ± 3.2 | 8.0 ± 2.9 | 0.483 |
HbA1c (%) |
10.1 ± 1.5 | 8.9 ± 1.3 | 0.000 |
Diabetes duration (months) |
113.7 ± 85.5 | 68.2 ± 66.6 | 0.000 |
Calcium (mmol/L) | 2.3 ± 0.1 | 2.3 ± 0.1 | 0.197 |
Carotid IMT (mm) |
1.3 ± 0.3 | 0.9 ± 0.1 | 0.000 |
Smoking history [ |
65 (36.5%) | 37 (27.2%) | 0.089 |
Family history of |
84 (47.2%) | 66 (48.5%) | 0.821 |
Hypertension |
86 (48.3%) | 43 (31.6%) | 0.004 |
Differences were assessed by the independent sample
Pearson’s correlation analyses showed that the carotid artery IMT was positively correlated with age, SBP, HbA1c, LDL-C, and diabetes duration but negatively correlated with the levels of serum 25(OH)D3 and calcium (
Correlation analysis: correlative factors of carotid IMT.
Variables |
|
|
---|---|---|
Age | 0.4 | 0.000 |
Diabetes duration | 0.3 | 0.000 |
SBP | 0.2 | 0.001 |
HbA1c | 0.4 | 0.000 |
LDL-C | 0.1 | 0.047 |
25(OH)D3 | −0.4 | 0.000 |
Calcium | −0.3 | 0.000 |
Smoking history | 0.1 | 0.037 |
Hypertension history | 0.2 | 0.001 |
Multivariate linear stepwise regression analysis was performed to evaluate the independent influence factors of carotid IMT. The analysis demonstrated that age (X1), HbA1c (X2), 25(OH)D3 (X3), and serum calcium (X4) were independently associated with carotid IMT. The regression equation was
Multiple linear regression analysis: independent influence factors of carotid artery IMT.
Independent |
Unstandardized coefficient |
|
|
Standardized | |
---|---|---|---|---|---|
|
Std. error | ||||
HbA1c | 0.06 | 0.010 | 5.42 | 0.000 | 0.27 |
Age | −0.01 | 0.001 | 7.84 | 0.000 | 0.36 |
25(OH)D3 | 0.01 | 0.002 | −3.93 | 0.000 | −0.20 |
Calcium | −0.39 | 0.123 | −3.20 | 0.002 | −0.15 |
Constant | 1.12 | 0.306 | 0.65 | 0.000 | — |
In this model, BMI, diabetes duration, SBP, and LDL-C were also included as covariates, but they were not independently associated with carotid IMT.
Logistic regression analysis: risk factor of carotid atherosclerotic plaque.
Risk factors |
|
OR | 95%CI |
|
---|---|---|---|---|
Age | 0.08 | 1.08 | 1.06–1.11 | 0.000 |
HbA1c | 0.72 | 2.06 | 1.65–2.56 | 0.000 |
LDL-C | 0.36 | 1.43 | 1.08–1.90 | 0.013 |
25(OH)D3 | −0.05 | 0.95 | 0.92–0.98 | 0.004 |
Diabetes duration | 0.01 | 1.01 | 1.01–1.01 | 0.000 |
Hypertension history | 0.70 | 2.02 | 1.27–3.22 | 0.003 |
Logistic regression analysis showed that age, diabetes duration, hypertension history, HbA1c, and LDL-C were risk factors of carotid plaque. Meanwhile, serum 25(OH)D3 was independently associated with the incidence of carotid plaques in patients with T2DM (OR = 0.95; 95%CI: 0.92~0.98,
Vitamin D3, as an essential fat-soluble vitamin, largely obtained from cutaneous exposure to ultraviolet radiation and to a lesser extent from dietary and supplements, is metabolized by the liver and then by the kidney to become 1,25-dihydroxyvitamin D3 91,25(OH)2D3), the tightly regulated activated molecule of vitamin D3, which can exert biological effect by combining with vitamin D receptor. However, 1,25(OH)2D3 has a very short half-life, so it is not generally used as a clinical biomarker to assess vitamin D status. 25(OH)D3, as the circulating storage form of vitamin D3, has a long-serum half-life, and it is easily to be detected. Accordingly, the quantitation of serum 25(OH)D3 provides a clinically useful assessment of vitamin D status [
Diabetic macrovascular complications are the major causes of mortality and disability among the patients with T2DM, of which the pathological basis is atherosclerosis, and its early change is the increasing artery intima-media thickness, especially the carotid IMT. A large number of studies have demonstrated that carotid IMT can be used as a suitable surrogate marker of macroangiopathy [
Our study showed that the carotid IMT levels in the lower 25(OH)D3 groups were greater than those in the higher 25(OH)D3 groups. The differences were still statistically significant after adjustment for sex, age, BMI, serum lipids, HbA1c, diabetes duration, blood pressure, smoking history, and other variables. Pearson’s correlation analysis showed that the carotid artery IMT was negatively correlated with the levels of serum 25(OH)D3. Multiple linear regression analysis showed that 25(OH)D3 was independently associated with carotid IMT, after adjusting for age, diabetes duration, systolic blood pressure, HbA1c, LDL-C, and serum calcium. Logistic regression analysis showed that low serum 25(OH)D3 was the risk factor of carotid plaque. The results as described above suggested that with the decreasing of serum 25(OH)D3 levels, carotid IMT and carotid plaque showed a trend of increasing.
In addition, the correlation analyses showed that carotid IMT correlated positively to age, diabetes duration, SBP, HbA1c, LDL-C, smoking history, and hypertension history. In regression analysis, age, diabetes duration, hypertension history, HbA1c, and LDL-C were also the risk factors of carotid plaque. And the influence of these factors on carotid IMT and atherosclerosis have been confirmed in a number of previous studies. As shown in our study, patients with lower serum 25(OH)D3 levels had a longer diabetes duration, higher SBP, HbA1c, LDL-C, and lower HDL-C than those with higher 25(OH)D3 levels. These results further demonstrated that it is helpful to prevent atherosclerosis by controlling blood glucose, blood pressure, and blood lipids.
In our study, serum calcium was independently correlated with carotid IMT. Currently, there is no final conclusion of the relationship between serum calcium status and carotid IMT among type 2 diabetic individuals. A study in north Manhattan showed that subjects with no carotid plaque had lower serum calcium levels within the normal range than those with carotid plaque [
The following four aspects might be important for the effects of vitamin D on atherosclerosis: (1) Vitamin D can increase the expression of Ca-ATRase in vascular endothelial cells and smooth muscle cells, elevate cytosolic free calcium concentrations, induce contractile proteins expression, and then promote production of prostacyclin (PGI2), which affects the vascular tone; Vitamin D can improve endothelial function by inhibiting the inflammatory reaction and oxidative injury [
In conclusion, serum 25(OH)D3 was negatively correlated with carotid IMT and the incidence of carotid plaques in patients with T2DM. When serum 25(OH)D3 concentration is below a certain level, the incidence of atherosclerosis in type 2 diabetic patients may increase. Vitamin D deficiency may predict subclinical atherosclerosis in diabetic patients, and vitamin D supplementation might be a clinical intervention to prevent atherosclerosis in patients with T2DM. Remarkably, our study is a cross-sectional one. It is necessary to carry out further follow-up and researches.
The authors declare that they have no conflicts of interest.