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Table 1 Randomized studies comparing the effect of vitamin D supplementation on iron status

From: The effect of vitamin D supplementation on hemoglobin concentration: a systematic review and meta-analysis

Study

Study design

Population

Duration of intervention

Season of intervention

Vitamin D dose and type in intervention group

Comparator group treatment

Baseline 25(OH)D (ng/ml)

Outcome

Conclusion

Trautveffer, 2014, Germany [47].

Parallel RCT - double blind

60 healthy subjects (F=36, M=24), age 20-70 yr.

8 weeks

Winter

Fortified bread with 400 IU, vit D3

Placebo bread

I=20±6.4 P=23.6± 12

↔ Iron

↔ ferritin,

↔ trans%

No effect

Miskulin, 2015, USA [41].

Parallel RCT - double blind

276 CKD Patients, average age 61 yr.

6 months

Not reported

Oral dose of 50,000 IU, vit D2

Placebo pills

I=16.06±5.9

P=16.96±6.4

↔ ferritin

No effect

Toxqui, 2015, Spain [46].

Parallel RCT - double blind

109 anemic women, age 18-35 yr.

8 and 16 weeks

Not reported

Fortified dry milk with 200 IU vit D3 and 15 mg iron

Fortified dry milk with 15 mg iron

Not reported

↓ Iron

↔ ferritin

↔ trans%

↔ Hb

No effect

Sooragonda, 2015, India [45].

Parallel RCT - single blind

30 anemic subjects, age 18-65 yr.

12 weeks

Winter

0.6 Lakh Amp vit D3+ Amp iron

Amp normal saline + Amp iron

I=10.3±5.2

C=11.6±3.7

↔ ferritin

↔ Hb

No effect

Smith, 2016, USA [44].

Parallel RCT - double blind

28 healthy subjects (F=22, M=6), age 18-65 yr.

1 week

Winter

Oral dose of 250,000 IU, vit D3

Oral placebo

I=16.75±1.9

P=16.7±2.03

↔ ferritin

No effect

Smith, 2016, USA [53].

Parallel RCT - double blind

30 mechanically ventilated critically ill adults (F=11, M=19, average age 63.1 yr.

4 weeks

Not reported

Enteral dose of 500,000 IU (I1) and 250,000 IU (I2) vit D3

Enteral placebo

I1=10±90.9

I2=7±77.8

P=8 ±80

↑ Hb

Positive effect

Madar, 2016, Norway [42].

Parallel RCT - double blind

251 healthy subjects, age 18-50 yr.

16 weeks

Late winter

I1=tablet 1000 IU, vit D3

I2= tablet 400 IU, vit D3

Placebo tablet

I1=10.8±6.8

I2=12.4±8.8

P=12.4±8

↔ Iron

↔ Hb

↔ ferritin

↔ trans%

No effect

Hennigar, 2016, USA [40].

Parallel RCT - double blind

152 military trained subjects (F=55, M=98), age 18-42 yr.

9 weeks

Winter

Fortified bar with 1000 IU vit D3 + 2000 mg calcium

Placebo bar

Not reported

↔ Hb

↔ ferritin

↔ trans%

No effect

Ernest, 2016, Germany [50].

Parallel RCT - double blind

200 hypertensive patients (F=94, M=106), average age 60.5 yr.

8 weeks

Summer

Oral dose of 2800 IU IU/ day, vit D3

Placebo tablet

I= 22 ± 5.6

C:20.4±5.6

↔ Hb

No effect

Ernest, 2017, Germany [49].

Parallel RCT - double blind

172 heart failure patients (F=59, M=113), age 18-79 yr.

36 months

Autumn, winter, spring

Oral dose of 4000 IU/ day, vit D3

Placebo drop

I=13.2± 5.6

C:14± 2.4

↔ Hb

No effect

Jastrzebska, 2017, Poland [51].

Parallel RCT - double blind

36 soccer player (M=36), average age 17.5 yr.

8 weeks

Winter

Oral dose of 5000 IU/ day, vit D3

Placebo drop

I=19.6± 3.6

C:19.2±6.4

↔ Hb

No effect

Dahlquist, 2017, Columbia [48].

Cross over RCT - single blind

10 highly-trained cyclists men, age 18-45 yr.

3 hours

Not reported

Sport drink with 5000 IU vit D3 + 1000 mcg vit k2

Placebo drink

I=30± 11.2

↔ Iron

↔ Hb

↔ ferritin

No effect

Walentukiewicz, 2018, Poland [52].

Parallel RCT - double blind

94 elderly women, average age 68 yr.

12 weeks

Not reported

Oral dose of 28,000 IU/ week, vit D3

Placebo drop

I=27.37±8.14

C:24.64±11.61

↑ ferritin

Positive effect

Panwar, 2018, USA [43].

Parallel RCT - double blind

40 CKD Patients, average age 60.5 yr.

6 weeks

Not reported

Oral dose of 0/5 mcg/ day, calcitriol

Placebo tablet

Not reported

↔ Hb

↔ ferritin

↔ trans%

No effect

  1. Abbreviations: RCT randomized clinical trials, IDA iron deficiency anemia, VDD vitamin d deficiency, F female, M male, IU international unit, Vit vitamin, Hb hemoglobin, Trans % transferrin saturation, ↑ significant increase, ↔ not significant change, ↓ significant decrease