Are Systematic Screening for Vitamin D Deficiency and Vitamin D Supplementation Currently Feasible for Ankylosing Spondylitis Patients?

Table 1

Published cross-sectional studies assessing vitamin D deficiency prevalence in AS patients versus healthy subjects.

Author, year of publication, and location	Definition	Sample size		Groups matching for			Vitamin D supplementation	Results
		AS	Controls	Age	Gender	BMI
Klingberg et al., 2016, Sweden [21]	Insufficiency < 50 nmol/l; Deficiency < 25 nmol/l	203	120	No	No	No	Not excluded	No significant difference between AS patients and HCs (51 nmol/l [IQR 37.0–67.0] versus 45.0 nmol/l [IQR 32.0–59.0], for serum 25[OH]D and % versus %, for deficiency)
Hmamouchi et al., 2013, Morocco [22]	Insufficiency 20–30 ng/ml; Deficiency < 20 ng/ml	70	140	Yes	No	Yes	Not excluded	Significant lower levels of 25(OH)D in AS patients compared with HCs ( ng/ml versus  ng/ml, ) and significant deficiency in AS patients compared with HCs; (62 [88.6%] versus 57 [40.7%], )
Erten et al., 2013, Turkey [18]	Insufficiency < 30 ng/ml; Deficiency < 10 ng/ml	48	92	NR	NR	NR	Not excluded	Significant reduced vitamin D levels in AS patients compared with HCs (); Insufficiency significantly more prevalent in AS patients than in HCs (38 [80%] versus 57 [62%], ); Deficiency significantly more prevalent in AS patients than in HCs (8 [17%] versus 4 [4%], )
Yazmalar et al., 2013, Turkey [23]	NR	72	70	No	No	No	Not excluded	No statistical difference in terms of seasonal 25(OH)D levels of AS patients compared with HCs ( ng/ml versus  ng/ml in the summer and  ng/ml versus  ng/ml in the winter)
Durmus et al., 2012, Turkey [19]	Insufficiency 20.1–29.9 ng/ml; Deficiency ≤ 20 ng/ml	99	42	Yes	Yes	Yes	Excluded	No statistical difference in serum 25(OH)-D3 in AS patients compared with HCs ( ng/ml versus  ng/ml, )
Mermerci Başkan et al., 2010, Portugal [24]	NR	100	58	Yes	Yes	Yes	Not excluded	The mean serum 25(OH)-D3 was significantly lower in AS patients as compared to HCs ( mmol/l versus  mmol/l, )
Lange et al., 2005, Germany [25]	NR	58	58	Yes	Yes	No	Not excluded	Significant reduction of vitamin D metabolites in both AS patients with and without osteoporosis compared with HCs ( pg/ml versus  pg/ml versus  pg/ml, for 1.25 vitamin D3 and  ng/ml versus  ng/ml versus  ng/ml, for 25-vitamin D3
Obermayer-Pietsch et al., 2003, Germany [26]	NR	104	54	Yes	Yes	Yes	Not excluded	Significant lower vitamin D levels in AS patients compared with HCs ()
Lange et al., 2001, Germany [27]	Normal range: 6–42 ng/ml	70	45	Yes	Yes	No	Not excluded	The mean serum 1,25(OH)2-D3 was significantly lower in AS patients as compared with HCs ( pg/ml versus  pg/ml, ); There was no significant difference in the mean serum 25(OH)-D3 in AS patients () as compared to HCs (),
Franck and Keck, 1993, Germany [28]	NR	38	52	No	No	No	Not excluded	Mean vitamin D metabolite concentrations were in the normal range in both AS patients and HCs (comparative values not given)

AS: ankylosing spondylitis; BMI: body mass index; HCs: healthy controls; NR: not reported.
Definition according to the level of serum 25(OH)D.