SUPPLEMENTARY DATA Supplemental e-material

Supplementary Table 1. Search strategy Supplementary Table 2. Data extraction form Supplementary Table 3. Excluded trials and reason(s) for exclusion Supplementary Table 4. Inclusion criteria of included studies Supplementary Table 5. Summary of Findings and Strength of Evidence in Studies (GRADE） Supplementary Table 6. Subgroup analysis of the effect of vitamin D on reversion of prediabetes to normal Supplementary Table 7. RCTs included in previous meta-analysis and this study on effects of vitamin D supplementation on new-onset T2DM Supplementary Table 8. Characteristics of this study and previous meta-analyses on effects of vitamin D supplementation on new-onset T2DM Supplementary Figure 1. Risk of bias summary Supplementary Figure 2. Risk of bias graph: review authors' judgements about each risk of bias item presented as percentages across all included studies Supplementary Figure 3. Funnel plot of studies on new-onset T2DM Supplementary Figure 4. Forest plot of new-onset T2DM within trials evaluating vitamin D supplementation, stratified by mean BMI (BMI ≥30 or BMI <30) Supplementary Figure 5. meta-regression of the effect of dose of vitamin D on new-onset T2DM Supplementary Figure 6. meta-regression of the effect of duration of vitamin D on new-onset T2DM

©2020 American Diabetes Association. Published online at https://care.diabetesjournals.org/lookup/suppl/doi:10.2337/dc19-1708/-/DC1 SUPPLEMENTARY DATA Supplementary Table 1. Search strategy

Database: EBM Reviews - Cochrane Central Register of Controlled Trials Search Strategy: ------1 exp Vitamin D/ad, ae, pd, tu (55) 2 ((vit-d? or vitamin-d? or dihydroxyvitamin D? or dihydroxy-vitamin D? or hydroxyvitamin D? or hydroxyl-vitamin d? or dihydrotachysterol or colecalciferol or epicalcitriol or oxacalcitriol or alfacalcidol or calcifediol I or calciferol? or calcipotriol or calcitriol or dihydroxycolecalciferol or hydroxycolecalciferol or seocalcitol or tacalcitol or oxavitamin or hydroxycholecalciferol? or calcidiol or calcipotriene or dihydroxycholecalciferol? or dihydroxy-cholecalciferol or cholecalciferol? or ergocalciferol? or epiergocalciferol or dihydroxyergocalciferol or dihydroxy-ergocalciferol or hydroxyl- ergocalciferol or hydroxyergocalciferol or doxercalciferol or hydroxycalciferol or hydroxyl-calciferol or dihydroxy-calciferol or dihydroxycalciferol or dihydrotachysterin or calcamine or ercalcidiol) adj5 (supplement* or therap* or treat* or prevent* or daily or receiv* or regimen or dose? or oral* or intramuscular or inject*)).mp. (9467) 3 exp Diabetes Mellitus, Type 2/ (15335) 4 exp Insulin Resistance/ (4816) 5 (diabet* or prediabet*).ti,ab. (79696) 6 Glucose Intolerance/ (958) 7 impaired glucose toleranc*.ti,ab. (1842) 8 IGT.ti,ab. (914) 9 impaired fasting glucose.ti,ab. (637) 10 IFG.ti,ab. (477) 11 insulin resist*.ti,ab. (9754) 12 glucose intoleranc*.ti,ab. (592) 13 MODY.ti,ab. (22) 14 (dm2 or dm-2).ti,ab. (399) 15 (NIDDM or IIDM).ti,ab. (1072) 16 non-insulin depend*.ti,ab. (2055) 17 noninsulin depend*.ti,ab. (146) 18 noninsulindepend*.ti,ab. (1) 19 non insulin?depend*.ti,ab. (5) 20 or/3-19 (87230) 21 (1 or 2) and 20 (1064)

*************************** Database: Ovid MEDLINE(R) and Epub Ahead of Print, In-Process & Other Non-Indexed Citations, Daily and Versions(R) Search Strategy: ------1 exp Vitamin D/ad, ae, pd, tu (31001) 2 ((vit-d? or vitamin-d? or dihydroxyvitamin D? or dihydroxy-vitamin D? or hydroxyvitamin D? or hydroxyl-vitamin d? or dihydrotachysterol or colecalciferol or epicalcitriol or oxacalcitriol or alfacalcidol or calcifediol I or calciferol? or calcipotriol or calcitriol or dihydroxycolecalciferol or hydroxycolecalciferol or seocalcitol or tacalcitol or oxavitamin or hydroxycholecalciferol? or calcidiol or calcipotriene or dihydroxycholecalciferol? or dihydroxy-cholecalciferol or cholecalciferol? or ergocalciferol? or epiergocalciferol or dihydroxyergocalciferol or dihydroxy-ergocalciferol or hydroxyl- ergocalciferol or hydroxyergocalciferol or doxercalciferol or hydroxycalciferol or hydroxyl-calciferol or

©2020 American Diabetes Association. Published online at https://care.diabetesjournals.org/lookup/suppl/doi:10.2337/dc19-1708/-/DC1 SUPPLEMENTARY DATA dihydroxy-calciferol or dihydroxycalciferol or dihydrotachysterin or calcamine or ercalcidiol) adj5 (supplement* or therap* or treat* or prevent* or daily or receiv* or regimen or dose? or oral* or intramuscular or inject*)).mp. (24143) 3 randomized controlled trial.pt. (485029) 4 controlled clinical trial.pt. (93147) 5 random*.mp. (1285551) 6 placebo.ab. (199089) 7 drug therapy.fs. (2120951) 8 trial.ab. (469494) 9 groups.ab. (1930905) 10 or/3-9 (4745243) 11 exp animals/ not humans.sh. (4596228) 12 10 not 11 (4101587) 13 (1 or 2) and 12 (17677) 14 exp Diabetes Mellitus, Type 2/ (123520) 15 exp Insulin Resistance/ (77833) 16 (diabet* or prediabet*).ti,ab. (586862) 17 Glucose Intolerance/ (8222) 18 impaired glucose toleranc*.ti,ab. (10572) 19 IGT.ti,ab. (4699) 20 impaired fasting glucose.ti,ab. (3592) 21 IFG.ti,ab. (3325) 22 insulin resist*.ti,ab. (77253) 23 glucose intoleranc*.ti,ab. (9614) 24 MODY.ti,ab. (1159) 25 (dm2 or dm-2).ti,ab. (2501) 26 (NIDDM or IIDM).ti,ab. (6919) 27 non-insulin depend*.ti,ab. (10854) 28 noninsulin depend*.ti,ab. (1435) 29 noninsulindepend*.ti,ab. (4) 30 non insulin?depend*.ti,ab. (14) 31 or/14-30 (664772) 32 13 and 31 (1212)

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Database: Embase Search Strategy: ------1 exp vitamin D/ae, ct, ad, cb, cm, cr, do, dt, ei, ce, ci, dl, du, ig, ly, im, na, os, tl, ur, ut, va, iv, vi, po, pa, oc, pd, cj, sb, li, tp, td (42653) 2 ((vit-d? or vitamin-d? or dihydroxyvitamin D? or dihydroxy-vitamin D? or hydroxyvitamin D? or hydroxyl-vitamin d? or dihydrotachysterol or colecalciferol or epicalcitriol or oxacalcitriol or alfacalcidol or calcifediol I or calciferol? or calcipotriol or calcitriol or dihydroxycolecalciferol or hydroxycolecalciferol or seocalcitol or tacalcitol or oxavitamin or hydroxycholecalciferol? or calcidiol or calcipotriene or dihydroxycholecalciferol? or dihydroxy-cholecalciferol or cholecalciferol? or ergocalciferol? or epiergocalciferol or dihydroxyergocalciferol or dihydroxy-ergocalciferol or hydroxyl- ergocalciferol or hydroxyergocalciferol or doxercalciferol or hydroxycalciferol or hydroxyl-calciferol or dihydroxy-calciferol or dihydroxycalciferol or dihydrotachysterin or calcamine or ercalcidiol) adj5

©2020 American Diabetes Association. Published online at https://care.diabetesjournals.org/lookup/suppl/doi:10.2337/dc19-1708/-/DC1 SUPPLEMENTARY DATA (supplement* or therap* or treat* or prevent* or daily or receiv* or regimen or dose? or oral* or intramuscular or inject*)).mp. (38174) 3 1 or 2 (67152) 4 non insulin dependent diabetes mellitus/ (235403) 5 Insulin Resistance/ (116006) 6 (diabet* or prediabet*).ti,ab. (866031) 7 Glucose Intolerance/ (17272) 8 impaired glucose toleranc*.ti,ab. (15915) 9 IGT.ti,ab. (7700) 10 impaired fasting glucose.ti,ab. (5824) 11 IFG.ti,ab. (5475) 12 insulin resist*.ti,ab. (113306) 13 glucose intoleranc*.ti,ab. (13988) 14 MODY.ti,ab. (2020) 15 (dm2 or dm-2).ti,ab. (4796) 16 (NIDDM or IIDM).ti,ab. (7999) 17 non-insulin depend*.ti,ab. (12593) 18 noninsulin depend*.ti,ab. (1730) 19 noninsulindepend*.ti,ab. (13) 20 non insulin?depend*.ti,ab. (71) 21 or/4-20 (981693) 22 randomized controlled trial/ (557729) 23 crossover procedure/ (59791) 24 double blind procedure/ (162501) 25 single blind procedure/ (35692) 26 (random* or factorial* or crossover* or placebo* or assign* or allocat* or volunteer* or (doubl* adj5 blind*) or (singl* adj5 blind*)).mp. (2430151) 27 or/22-26 (2430151) 28 exp animal/ (24338801) 29 human/ (19724895) 30 28 not 29 (4613906) 31 27 not 30 (2195366) 32 3 and 21 and 31 (1443)

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©2020 American Diabetes Association. Published online at https://care.diabetesjournals.org/lookup/suppl/doi:10.2337/dc19-1708/-/DC1 SUPPLEMENTARY DATA Supplementary Table 2. Standard data extraction form

Correspon Study First Female Trial Country dence Email Populatio No. of patients author (%) author n

Baseline Mean Mean Follow- 25(OH)D Baseline 25(OH)D BMI Treatment Control age up vitamin D control (nmol/L) (kg/m2) (nmol/L)

New-onset T2DM Reversion of prediabetes to normal Event(I) Total(I) Event(C) Total (C) Event(I) Total(I) Event(C) Total (C)

Serum 25(OH)D concentration

Mean(I) SD(I) Total(I) Mean(C) SD(C) Total(C)

Fasting blood glucose

Mean(I) SD(I) Total(I) Mean(C) SD(C) Total(C)

HbA1c

Mean(I) SD(I) Total(I) Mean(C) SD(C) Total(C)

HOMA-IR

Mean(I) SD(I) Total(I) Mean(C) SD(C) Total(C)

Fasting insulin

Mean(I) SD(I) Total(I) Mean(C) SD(C) Total(C)

©2020 American Diabetes Association. Published online at https://care.diabetesjournals.org/lookup/suppl/doi:10.2337/dc19-1708/-/DC1 SUPPLEMENTARY DATA Supplementary Table 3. Excluded trials and reason(s) for exclusion

Trial Reason(s) for exclusion Pittas 2007(1) Mixed intervention of calcium plus vitamin D compared with placebo de Boer 2008(2) Mixed intervention of calcium plus vitamin D compared with placebo Avenell 2009(3) Not prediabetes Jorde 2010(4) Not prediabetes Mitri 2011(5) Follow-up less than 6 months Harris 2012(6) Follow-up less than 6 months Iraj 2012(7) Follow-up less than 6 months Carrillo 2013(8) Not prediabetes Oosterwerf 2014(9) Follow-up less than 6 months Sollid 2014(10) Duplicates, new results published in Jorde 2016(11) Asemi 2015(12) Not prediabetes de Courten 2015(13) Not a trial Tuomainen 2015(14) Follow-up less than 6 months Forouhi 2016(15) Follow-up less than 6 months Osati 2016(16) Not prediabetes Moreira-Lucas 2017(17) Follow-up less than 6 months Swart 2018(18) Not a trial

©2020 American Diabetes Association. Published online at https://care.diabetesjournals.org/lookup/suppl/doi:10.2337/dc19-1708/-/DC1 SUPPLEMENTARY DATA Supplementary Table 4. Inclusion criteria of included studies

Study Inclusion criteria Davidson Age ≥ 40 years 2013 25(OH)D < 75 nmol/l Prediabetes, defined as IFG and/or IGT (IFG, FPG 6.1–6.9 mmol/l; IGT, 2-h OGTT 7.8– 11.0 mmol/l) Dutta 2014 Age 30–80 years old 25(OH)D < 75 nmol/l Prediabetes, defined as persistent IFG and/or IGT (IFG, FPG 5.6- 6.9 mmol/l; IGT, 2-h OGTT 7.8–11.0 mmol/l) over two times OGTT within a week Barengolts African American men 2015 Age 35-85 years old BMI 28-39 kg/m2 25(OH)D 5.0 - 29 ng/ml Prediabetes, defined as FPG 5.5-7.0 mmol/l (95-125 mg/dl) and/or HbA1c 5.7-6.4% (38.8-46.5 mmol/mol) Kuchay Prediabetes, defined as FPG 5.6-7.0 mmol/l (100-125 mg/dl), 2-h OGTT 7.8-11.0 2015 mmol/l, and HbA1c 5.7-6.4% (38.8-46.5 mmol/mol) Jorde 2016 Age 25-80 years Prediabetes, defined as FPG6.0-6.9 mmol/l (108-124 mg/dl) and/or 2-h OGTT 7.8-11.0 mmol/l KAWAHARA Age ≥30 years old 2018 Serum calcium (corrected value) <11.0 mg/dL IGT, defined as FPG <126 mg/dL, 2-h OGTT 7.8-11.1 mmol/l, and HbA1c <6.5% (38.8- 46.5 mmol/mol) Niroomand Age 18-80 years old 2019 Prediabetes, defined as FPG ≥ 5.6-6.9 mmol/l, and 2-h OGTT 7.8-11.1 mmol/l Pittas 2019 Age ≥30 years old Prediabetes, defined as meeting at least two of three glycemic criteria: FPG 5.6-6.9 mmol/l (100-125 mg/dl), 2-h OGTT 7.8-11.0 mmol/l, and HbA1c 5.7-6.4% (39-47 mmol/mol) NR：not reported

©2020 American Diabetes Association. Published online at https://care.diabetesjournals.org/lookup/suppl/doi:10.2337/dc19-1708/-/DC1 SUPPLEMENTARY DATA Supplementary Table 5. Summary of Findings and Strength of Evidence in Studies

Relative Absolute effect estimates (per 1000) Quality Patients 2 Outcome effect I Vitamin (Studies) Control Difference (95% CI) D New-onset 4896 RR 0.89 25 fewer 0% 226 201 Moderate* T2DM (8) (0.80-0.99) (2 to 45 fewer) Reversion of 1080 RR 1.48 68 more prediabetes to 0% 141 209 High (5) (1.14-1.92) (20 to 130 fewer) normal

NE: not examined * moderate quality due to imprecision because of margin of 95% Confidence Intervals of the effect size

©2020 American Diabetes Association. Published online at https://care.diabetesjournals.org/lookup/suppl/doi:10.2337/dc19-1708/-/DC1 SUPPLEMENTARY DATA Supplementary Table 6. Subgroup analysis of the effect of vitamin D on reversion of prediabetes to normal

Subgroup title No. of No. of I2 Risk Ratio, 95%CI P for trials patients interaction Overall 5 1080 1.44 [1.11, 1.86] Baseline 25(OH)D (nmol/L) ≥50 2 620 0.31 1.33 [0.91, 1.95] 0.46 <50 3 460 0 1.65 [1.07, 2.54] Baseline 25(OH)D (nmol/L) ≥30 5 1080 0 1.44 [1.11, 1.86] <30 0 0 NA NA NA Achieved 25(OH)D in vitamin

D group (nmol/L) ≥75 5 1080 0 1.44 [1.11, 1.86] NA <75 0 0 NA NA Type of vitamin D Vitamin D 4 907 0 1.45 [1.11, 1.89] 3 0.86 Vitamin D2 1 173 NA 1.32 [0.48, 3.64] Daily dose equivalent (IU) ≥2000 5 1080 0 1.44 [1.11, 1.86] NA <2000 0 0 NA NA Mean Body–mass index

(kg/m2) ≥30 4 955 0 1.41 [1.06, 1.86] 0.38 <30 1 125 NA 1.93 [1.00, 3.71] Timing of treatment Daily 0 0 NA NA NA Intermittently 5 1080 0 1.44 [1.11, 1.86] Intervention Vitamin D vs placebo 4 955 0 1.37 [1.03, 1.81] Vitamin D + calcium vs 1 125 NA 1.93 [1.00, 3.71] 0.34 calcium Latitude ≥37o 1 511 1.60 [1.03,2.48]

<37o 4 569 1.36 [0.99,1.87] Follow-up Follow-up ≥3 years 1 511 NA 1.60 [1.03, 2.48] 0.64 Follow-up <3 years 4 569 0 1.41 [1.02, 1.94]

©2020 American Diabetes Association. Published online at https://care.diabetesjournals.org/lookup/suppl/doi:10.2337/dc19-1708/-/DC1 SUPPLEMENTARY DATA Supplementary Table 7. List of RCTs included in previous meta-analyses and in this study: Effects of vitamin D supplementation on new-onset T2DM

Reference, publication non‑diabetics Pre-diabetics year Seida He Tang Seida He 2018 Tang This Reason for exclusion 2014 2018 2018 2014 2018 study √ non‑diabetics; including Pittas 2007 VD+Ca vs procebo √ √ √ non‑diabetics; including De Boer 2008 VD+Ca vs procebo Avenell 2009 √ √ non‑diabetics Davidson 2013 √ √ √ √ √ √ √ Dutta 2014 √ √ √ √ √ √ √ √ √ early version of Jorde Sollid 2014 2016 Kuchay 2015 √ √ √ √ √ Barengolts 2015 √ Jorde 2016 √ √ √ Kawahara 2018 √ Niroomand 2019 √ Pittas 2019 √

RCT: Randomized controlled trial; T2DM: type 2 diabetes mellitus

©2020 American Diabetes Association. Published online at https://care.diabetesjournals.org/lookup/suppl/doi:10.2337/dc19-1708/-/DC1 SUPPLEMENTARY DATA Supplementary Table 8. Characteristics of this study and previous meta-analyses: Effects of vitamin D supplementation on new-onset T2DM

Methods Non‑diabetics Pre-diabetics Seida 2014 He 2018 Tang 2018 Seida 2014 He 2018 Tang 2018 This study Number of 4 6 6 1 5 4 8 trials Number of 38,811 NR 39,633 108 NR 853 4,788 patients Intervention Vitamin D3 Vitamin D Vitamin D Vitamin D3 Vitamin D Vitamin D Vitamin D Statistical Mantel- inverse- Mantel- Mantel- inverse- Mantel- NR method Haenszel variance Haenszel Haenszel variance Haenszel Analysis Random Fixed Random Random Fixed Random Fixed Model effect effect effect effect effect effect effect Result OR 1.02 RR 0.86 RR 1.01 OR 1.37 RR 0.84 RR 0.83 RR 0.89 (0.94-1.10) (0.74-1.01) (0.93-1.08) (0.41-4.62) (0.70-1.00) (0.57-1.20) (0.70-0.99)

NR: not reported; T2DM: type 2 diabetes mellitus

©2020 American Diabetes Association. Published online at https://care.diabetesjournals.org/lookup/suppl/doi:10.2337/dc19-1708/-/DC1 SUPPLEMENTARY DATA Supplementary Figure 1. Risk of bias summary: review authors' judgements about each risk of bias item for each included study.

©2020 American Diabetes Association. Published online at https://care.diabetesjournals.org/lookup/suppl/doi:10.2337/dc19-1708/-/DC1 SUPPLEMENTARY DATA Supplementary Figure 2. Risk of bias graph: review authors' judgements about each risk of bias item presented as percentages across all included studies

©2020 American Diabetes Association. Published online at https://care.diabetesjournals.org/lookup/suppl/doi:10.2337/dc19-1708/-/DC1 SUPPLEMENTARY DATA Supplementary Figure 3. Funnel plot of new-onset T2DM

©2020 American Diabetes Association. Published online at https://care.diabetesjournals.org/lookup/suppl/doi:10.2337/dc19-1708/-/DC1 SUPPLEMENTARY DATA Supplementary Figure 4. Forest plot of new-onset T2DM within trials evaluating vitamin D supplementation, stratified by mean BMI (BMI ≥30 or BMI <30)

©2020 American Diabetes Association. Published online at https://care.diabetesjournals.org/lookup/suppl/doi:10.2337/dc19-1708/-/DC1 SUPPLEMENTARY DATA Supplementary Figure 5. meta-regression of the effect of dose of vitamin D on new-onset T2DM

©2020 American Diabetes Association. Published online at https://care.diabetesjournals.org/lookup/suppl/doi:10.2337/dc19-1708/-/DC1 SUPPLEMENTARY DATA Supplementary Figure 6. meta-regression of the effect of duration of vitamin D on new-onset T2DM

©2020 American Diabetes Association. Published online at https://care.diabetesjournals.org/lookup/suppl/doi:10.2337/dc19-1708/-/DC1 SUPPLEMENTARY DATA References

1. Pittas AG, Harris SS, Stark PC, Dawson-Hughes B: The effects of calcium and vitamin D supplementation on blood glucose and markers of inflammation in nondiabetic adults. Diabetes care 2007;30:980-986 2. de Boer IH, Tinker LF, Connelly S, Curb JD, Howard BV, Kestenbaum B, Larson JC, Manson JE, Margolis KL, Siscovick DS, Weiss NS: Calcium Plus Vitamin D Supplementation and the Risk of Incident Diabetes in the Women's Health Initiative. Diabetes care 2008;31:701-707 3. Avenell A, Cook JA, MacLennan GS, McPherson GC, group Rt: Vitamin D supplementation and type 2 diabetes: a substudy of a randomised placebo-controlled trial in older people (RECORD trial, ISRCTN 51647438). Age Ageing 2009;38:606-609 4. Jorde R, Sneve M, Torjesen PA, Figenschau Y, Hansen J-B, Grimnes G: No significant effect on bone mineral density by high doses of vitamin D-3 given to overweight subjects for one year. Nutrition Journal 2010;9 5. Mitri J, Dawson-Hughes B, Hu FB, Pittas AG: Effects of vitamin D and calcium supplementation on pancreatic beta cell function, insulin sensitivity, and glycemia in adults at high risk of diabetes: the Calcium and Vitamin D for Diabetes Mellitus (CaDDM) randomized controlled trial. American Journal of Clinical Nutrition 2011;94:486-494 6. Harris SS, Pittas AG, Palermo NJ: A randomized, placebo-controlled trial of vitamin D supplementation to improve glycaemia in overweight and obese African Americans. Diabetes Obesity & Metabolism 2012;14:789-794 7. Iraj B, Aminorroaya A, Amini M: Does the intramuscular injection of vitamin D increase insulin resistance? J Res Pharm Pract 2012;1:60-65 8. Carrillo AE, Flynn MG, Pinkston C, Markofski MM, Jiang Y, Donkin SS, Teegarden D: Impact of vitamin D supplementation during a resistance training intervention on body composition, muscle function, and glucose tolerance in overweight and obese adults. Clinical Nutrition 2013;32:375-381 9. Oosterwerff MM, Eekhoff EM, Van Schoor NM, Boeke AJ, Nanayakkara P, Meijnen R, Knol DL, Kramer MH, Lips P: Effect of moderate-dose vitamin D supplementation on insulin sensitivity in vitamin D-deficient non-Western immigrants in the Netherlands: a randomized placebo-controlled trial. The American journal of clinical nutrition 2014;100:152-160 10. Sollid ST, Hutchinson MYS, Fuskevag OM, Figenschau Y, Joakimsen RM, Schirmer H, Njolstad I, Svartberg J, Kamycheva E, Jorde R: No Effect of High-Dose Vitamin D Supplementation on Glycemic Status or Cardiovascular Risk Factors in Subjects With Prediabetes. Diabetes care 2014;37:2123-2131 11. Jorde R, Sollid ST, Svartberg J, Schirmer H, Joakimsen RM, Njolstad I, Fuskevag OM, Figenschau Y, Hutchinson MY: Vitamin D 20,000 IU per Week for Five Years Does Not Prevent Progression From Prediabetes to Diabetes. The Journal of clinical endocrinology and metabolism 2016;101:1647-1655 12. Asemi Z, Foroozanfard F, Hashemi T, Bahmani F, Jamilian M, Esmaillzadeh A: Calcium plus vitamin D supplementation affects glucose metabolism and lipid concentrations in overweight and obese vitamin D deficient women with polycystic ovary syndrome. Clinical Nutrition 2015;34:586-592 13. de Courten B, Mousa A, Naderpoor N, Teede H, de Courten MP, Scragg R: Vitamin D supplementation for the prevention of type 2 diabetes in overweight adults: study protocol for a randomized controlled trial. Trials 2015;16:335 14. Tuomainen T-P, Virtanen JK, Voutilainen S, Nurmi T, Mursu J, de Mello VDF, Schwab U, Hakumaki M, Pulkki K, Uusitupa M: Glucose Metabolism Effects of Vitamin D in Prediabetes: The VitDmet Randomized Placebo-Controlled Supplementation Study. Journal of diabetes research 2015; 15. Forouhi NG, Menon RK, Sharp SJ, Mannan N, Timms PM, Martineau AR, Rickard AP, Boucher BJ, Chowdhury TA, Griffiths CJ, Greenwald SE, Griffin SJ, Hitman GA: Effects of vitamin D-2 or D-3 supplementation on glycaemic control and cardiometabolic risk among people at risk of type 2 diabetes: results of a randomized double-blind placebo-controlled trial. Diabetes Obesity & Metabolism

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©2020 American Diabetes Association. Published online at https://care.diabetesjournals.org/lookup/suppl/doi:10.2337/dc19-1708/-/DC1