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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