Serum 25-Hydroxyvitamin D Levels in Type 2 Diabetes Patients in North China: Seasonality and the Association between Vitamin D Status and Glycosylated Hemoglobin Levels

Table 1

Clinical characteristics of enrolled subjects.

Variables	Baseline N = 1074	Spring n = 386 (35.9%)	Summer n = 246 (22.9%)	Autumn n = 219 (20.4%)	Winter n = 223 (20.8%)
Age (years)	57 (49–66)	58 (48–67)	57 (48–67)	58 (52–66)	57 (49–66)	0.844
Sex
Male (n, %)	649 (60.4%)	241 (62.4%)	139 (56.5%)	131 (59.8%)	138 (61.9%)
Female (n, %)	425 (39.6%)	145 (37.6%)	107 (43.5%)	88 (40.2%)	85 (38.1%)
Duration of DM (years)	9 (3–15)	8 (3–15)	10 (3–15)	9 (3–15)	8 (3–15)	0.647
BMI (kg/m^2)	26.20 (23.78–28.68)	26.21 (23.80–28.41)	25.60 (23.44–28.65)	26.87 (24.22–29.21)	26.12 (24.00–28.68)	0.056
SBP (mmHg)	133 (122–147)	132 (121–145)	133 (120–143)^△	133 (123–150)	136 (124–148)	0.007
DBP (mmHg)	81 (74–90)	81 (74–89)	79 (72–89)^△	82 (75–90)	83 (75–91)	0.028
Albumin (g/L)	41.9 (39.3–44.3)	41.8 (39.4–44.2)	42.6 (39.6–44.5)	41.4 (39.4–44.2)	41.8 (38.8–44.5)	0.390
TC (mmol/L)	4.75 (3.94–5.62)	4.68 (3.88–5.63)	4.73 (3.85–5.57)	4.74 (3.93–5.58)	4.87 (4.22–5.51)	0.502
TG (mmol/L)	1.45 (1.01–2.24)	1.45 (0.99–2.15)	1.45 (1.01–2.39)	1.52 (1.09–2.32)	1.43 (1.00–2.06)	0.415
LDL-C (mmol/L)	3.09 (2.46–3.69)	3.02 (2.40–3.69)	3.10 (2.42–3.71)	3.11 (2.48–3.76)	3.17 (2.57–3.56)	0.744
HDL-C (mmol/L)	1.08 (0.92–1.26)	1.08 (0.92–1.28)	1.10 (0.93–1.26)	1.06 (0.91–1.24)	1.07 (0.92–1.26)	0.726
ApoA1 (g/L)	1.20 (1.04–1.36)	1.19 (1.01–1.34)	1.19 (1.04–1.33)	1.23 (1.08–1.39)	1.23 (1.09–1.38)	0.011
Apob (g/L)	0.82 (0.67–0.99)	0.81 (0.67–0.98)	0.83 (0.65–1.02)	0.81 (0.68–1.00)	0.82 (0.69–0.96)	0.984
FBG (mmol/L)	8.32 (6.55–10.89)	8.53 (6.75–11.23)	8.42 (6.41–10.83)	7.84 (6.45–10.42)	8.29 (6.59–10.81)	0.177
HbA1c%	8.7 (7.4–10.4)	8.8 (7.5–10.7)	8.8 (7.4–10.7)	8.6 (7.5–10.1)	8.6 (7.3–10.2)	0.481
25(OH)D (ng/mL)	17.05 (13.58–22.39)	16.31 (12.97–21.14)	19.60 (15.44-25.52)^△△	18.28 (14.00–23.06)^△△	15.84 (12.31–20.36)	0.000
OC (ng/mL)	12.74 (9.99–15.97)	12.80 (9.81–16.04)	13.16 (10.26–17.33)	11.70 (9.71–14.91)^#	12.99 (10.27–16.49)	0.026
β-CTX (ng/mL)	0.39 (0.26–0.51)	0.39 (0.25–0.48)	0.40 (0.27–0.50)	0.42 (0.28–0.56)	0.38 (0.23–0.52)	0.107
PINP (ng/mL)	38.93 (29.75–49.48)	37.63 (28.74–46.73)	39.14 (29.47–50.64)	37.65 (30.17–49.58)	41.43 (30.99–50.47)	0.076
PTH (pg/mL)	38.32 (29.23–49.09)	41.79 (32.96–51.12)	36.52 (27.64-47.47)	34.32 (26.90–45.71)	38.16 (28.41–48.53)	0.000
Ca (mmol/L)	2.30 (2.22–2.37)	2.30 (2.23–2.37)	2.30 (2.22–2.38)	2.29 (2.22–2.36)	2.29 (2.21–2.36)	0.557
P (mmol/L)	1.22 (1.10–1.35)	1.19 (1.07–1.30)	1.25 (1.13–1.37)^△	1.24 (1.13–1.37)	1.20 (1.08–1.34)	0.000
TT3 (nmom/L)	1.55 (1.35–1.74)	1.55 (1.35–1.76)^△	1.59 (1.41–1.74)^△△	1.55 (1.36–1.77)^△	1.49 (1.27–1.67)	0.002
TT4 (nmom/L)	94.65 (82.97–106.62)	95.41 (82.96–107.90)^△△	97.35 (89.16–109.15)^△△	93.91 (81.88–106.80)^△#	89.08 (78.21–99.89)	0.000
FT3 (pmom/L)	4.50 (4.02–4.88)	4.56 (4.01–4.94)^△△	4.55 (4.19–4.94)^△△	4.43 (4.04–4.77)	4.36 (3.88–4.78)	0.001
FT4 (pmol/L)	16.60 (14.87–18.13)	16.62 (14.95–18.14)	16.64 (15.13–18.11)	16.51 (14.77–18.21)	16.31 (14.42–17.92)	0.327
TSH (μIU/mL)	1.90 (1.29–2.72)	1.87 (1.27–2.68)	1.92 (1.28–2.63)	1.90 (1.32–2.67)	1.95 (1.33–2.94)	0.801

Notes. Compared with spring, , ; Compared with summer, ^##, ^#; Compared with winter, ^△△, ^△. BMI, body mass index; SBP, systolic blood pressure; DBP, diastolic blood pressure; TC, total cholesterol; TG, triglyceride; LDL-C, low-density lipoprotein cholesterol; HDL-C, high-density lipoprotein cholesterol; ApoA1, apolipoproteinA1; Apob, apolipoprotein b; FBG: fasting blood glucose; OC, osteocalcin; β-CTX, β-C-terminal cross-linked telopeptide of type I collagen; P1NP, procollagen type 1 N-terminal propeptide; PTH, parathyroid hormone; Ca, calcium; P, phosphorus; TT3, triiodothyronine; TT4, tetraiodothyronine; FT3, free thyroxine; FT4, free tetraiodothyronine; TSH, thyroid-stimulating hormone. Bold values indicate statistically significant results.