Table 2.
Clinical and biochemical characteristics of the long-term studies**
| Author, year, country | Study design, N | Duration | Intervention | Age (Years) | Change in HbA1c and HOMA | comments |
|---|---|---|---|---|---|---|
| Witham [29] 2010, UK* | RCT, N = 61 | 16 Weeks | Vitamin D3 100,000 or 200,000 IU single dose | 65 ± 11 | HbA1c 7.0 ± 1.6 vs. 6.9 ± 1.5 | HOMA-IR and HbA1c did not improve |
| HOMA-IR11.7 ± 12.7 vs. 15.9 ± 14.3 | ||||||
| Patel [34], 2010, USA | RCT, N = 24 | 4 Months | Vitamin D3 400 or 1200 IU | 58 ± 3 | HbA1c 6.7 ± 0.3 vs. 6.9 ± 0.2 | QUICKI & HbA1c did not improve |
| QUICKI 0.35 ± 0.01 vs. 0.35 ± 0.011 | ||||||
| Jorde [32], 2009, Norway | RCT, N = 32 | 6 Months | Vitamin D3 (40,000 IU/week) | 58 ± 10 | HbA1c 8.0 ± 1.3 at baseline and changed by −0.2 ± 0.9 (p=.90 vs. change in the placebo group) | Insulin resistance and HbA1c did not change |
| HOMA-IR 27.6 ± 34.3 at baseline and changed by 0.3 ± 23.5 (p=.58 vs. change in placebo group) | ||||||
| Jehle [38], 2014, Switzerland | RCT, N = 55 | 6 Months | 300,000 IM | 67 ± 3 | Significant intergroup difference in the ΔHbA1c (relative change + 2.9 ± 1.5% in the vitamin D group vs. +6.9 ± 2.1% in placebo group. HOMA-IR decreased by 13 ± 6% in the vitamin D group and increased by 10 ± 5% in the placebo group (p = 0.032) | Improved HOMA-IR and HbA1c |
| Strobel [15], 2014, Germany | RCT, N = 86 | 6 Months | Vigantol oil once a week (1904 IU) | 61 (36–78) | Groups: 25 (OH) vitamin D >20 vs. ≤20 ng/ml. | No effects on metabolic parameters |
| HbA1c 50 vs. 54 mmol/mol Hb, p = NS | ||||||
| Huang [11], 2012, China | Longitudinal, N = 22 | 6 Months | Vitamin D3 800 IU/d | 61 ± 10 | HbA1c 7.1 ± 1.4 vs. 7.2 ± 1.4, p = 0.86 | HbA1c remained stable |
| No data on HOMA parameters | ||||||
| Alam [16], 2014, UK | Retrospective audit, N = 204 | 8.0 ± 4.0 months | Vitamin D2 or vitamin D3*** | 61 ± 12 | HbA1c 8.5 ± 1.7 vs. 8.0 ± 1.5 after treatment in ergocalciferol treated patients | HbA1c levels improved with ergocalciferol than cholecalciferol |
| No data on HOMA parameters | ||||||
| Breslavsky [17], 2013, Israel | RCT, N = 24 | 12 Months | Vitamin D3 1000 IU | 67 ± 9 | HbA1c 7.0 ± 1.1 vs. 7.3 ± 1.1, p = 0.212 | No effect on glycemic parameters |
| HOMA-IR 4.2 vs. 6.1, p=.243, HOMA-B 84.7 vs. 42.5, p = 0.184 | ||||||
| Al-Daghri [20], 2012, Saudi | Prospective longitudinal, N = 92 | 18 months | Vitamin D3 2000 IU | 54 ± 10 | No data on HbA1c | HOMA-B showed improvement until 18 months |
| HOMA-B: 52 ± 9 vs. 97 ± 15, p = 0.002 |
IM: Intramuscular, RCT: Randomized controlled trial. *This study has provided data on both short term and long term changes in glycemic parameters.
**Studies with a follow up of > 3 months were considered as long-term studies.
1QUICKI: An index of insulin sensitivity.
***Vitamin. D2 50,000 IU/d *10 d followed by 24,000 IU Vitamin D3/month OR Vitamin D3 40,000/d *10 d followed by 24,000/40,000 IU monthly.