Table 1 Characteristics of included cross-sectional studies

Cemlyn-Jones et al. [33]

2008

Portugal

CF

Both

26.3 ± 8

22

4 (18)

18 (81.8)

Normal range (10 to 60 ng/mL)

–

NO

Study carried out over a six-month period

7

Chirita-Emandi et al. [34]

2017

UK

CF children that had at least one DXA scan performed over a period of 10 years

Both

12.04 ± 1.89

94

37 (39)

34 (36)

Insufficiency 25–50 nmol/L

Liquid chromatography tandem mass spectrometry (LC–MS/MS) using commercial standard in human serum (Chromsystems, München, Germany)

NO

–

7

Coriati et al. [36]

2015

Canada

CF

Both

27.5 ± 8.8

178

103 (57.86)

75 (42.14)

Deficiency\insufficient (suboptimal) < 75 nmoL/L

High-performance liquid chromatography coupled with tandem mass spectrometry (TQ Detector, Waters, Milford, MA, USA)

– > 

All those who had a 25(OH)D value measured at the same time were included in our study

6

Ciuna et al. [35]

2019

Romania

CF

–

–

58

43 (75)

15 (24)

25 nmol/l is generally regarded as the lower limit of normal

liquid chromatography tandem mass spectrometry

NO

–

7

Bellini et al. [32]

2021

USA

CF

Both

11.2 ± 3.6

75

17 (23)

58 (76)

Deficiency 10–30 ng/mL, insufficiency (30- 50 ng/mL

–

NO

Winter, Spring

6

Aziz et al. [31]

2021

Pakistan

CF

Both

9.45 ± 4.57

69

22 (31.88)

19 (27.53)

Deficient < 20 ng/ml

A radioimmunoassay kit

NO

All 4 seasons

7

Grey et al. [39]

2015

USA

CF

Both

12.6 ± 2.9

81

75 (95)

6 (5)

 < 20–40 mg/dl

25 OHD < 10 = LOW

25 OHD > 18 = Normal

–

Yes

May to October)

and

November to April),

7

Elkin et al. [35]

2001

UK

CF

Both

28 ± 8

104

86 (83)

18 [17]

Marginal (10.0–18.0)

–

Yes

Significantly higher values were found in the summer and autumn

6

39 (36)

18 (17)

 ≤ 0 nmol/l insufficient

–

Yes

Significantly higher values were found in the summer and autumn

6

Gordon et al. [38]

2007

USA

CF

Both

31.4 ± 9.1

64

25 (39)

39 (60)

 < 25 nmol/l deficiency

by radioimmunoassay

(Diasorin, Stillwater, MN)

Yes

The deficiency was more common during winter:

12 cases identified with mean 25OHD for winter participants of 29.5 ± 20.2 nmol/L vs one

case during summer with mean 25OHD for summer participants of 59.8 ± 23.5 nmol/L

(P < 0.001)

7

Haworth et al. [41]

1999

UK

CF

Both

25.3 ± 7.1

139

53 (38)

–

 < 37.5 nmol/L

–

No

All 4 seasons

7

30 (22)

–

 < 15 ng/ml insuf

–

–

–

6

10 (7)

–

 < 10 ng/ml def

–

–

–

7

Gupta et al. [40]

2017

India

CF

Both

12.8 ± 25.9

52

12 (23.1)

3 (5.77)

In patients with cystic fibrosis, total 25-OH-vitamin D levels below 30 were considered sub-optimal

25-hydroxyvitamin D (25 (OH) D) was measured using chemiluminescent immunoassay (DiaSorin LIAISON, Minnesota, USA)

NO

–

7

37 (71.2)

3 (5.77)

15–19 ng/mL insufficient

25-hydroxyvitamin D (25 (OH) D) was measured using chemiluminescent immunoassay (DiaSorin LIAISON, Minnesota, USA)

NO

–

6

McCauley et al. [42]

2013

USA

CF

Both

8 ± 1

28

3 (11)

24 (86)

Deficiency < 30 ng/mL

Liquid chromatography/tandem mass spectrometry

NO

All 4 seasons

7

8 ± 1

28

1 (4)

24 (86)

Sufficient (> 30 mg/L), insufficient (20–29 mg/L)

liquid chromatography/tandem mass spectrometry

NO

All 4 seasons

12 ± 0.75

47

15 (32)

27 (56)

Deficient (< 20 mg/L)

Liquid chromatography/tandem mass spectrometry

NO

All 4 seasons

12 ± 0.75

47

5 (11)

27 (56)

Sufficient (> 30 mg/L), insufficient (20–29 mg/L)

Liquid chromatography/tandem mass spectrometry

NO

All 4 seasons

16 ± 0.75

51

14 (27)

30 (58)

Deficient (< 20 mg/L)

Liquid chromatography/tandem mass spectrometry

NO

All 4 seasons

16 ± 0.75

51

7 (14)

30 (58)

Sufficient (> 30 mg/L), insufficient (20–29 mg/L)

Liquid chromatography/tandem mass spectrometry

NO

All 4 seasons