Vitamin D
Brief description
Vitamin D is a fat soluble nutrient critical for human survival. It can be obtained from two main sources – the sun (D3) and diet (D3 & D2).
Vitamin D2 is made from plants and is found in fortified foods and supplements. D3 is naturally produced in the human body and found in animal foods. It appears D3 supplements appear to raise blood levels of vitamin D (& sustain them longer) more than D2(1, 2).
Dietary sources:
Fatty fish (salmon, tuna, swordfish, sardines) & fish liver oils.
Smaller amounts in: egg yolk, cheese, beef liver.
Fortified foods.
Suggested mechanisms:
For diabetes: Vitamin D modulates insulin synthesis and secretion. The pancreatic islet cells contain all the components of the vitamin D endocrine system. Vitamin D may also reduce insulin resistance with its receptors in fat cells (adipocytes), muscle and liver cells (hepatocytes)(3).
Evidence base
Strength & Muscle function: Supplementation with vitamin D was unable to significantly improve strength, power and/or muscle function in both athletes(4, 5), non-athletes(6) – including post-menopausal women(7).
Diabetes: In individuals who are prediabetic (HbA1c 42-47mmol/L) & not obese, vitamin D supplementation may help to reverse this diagnosis and reduce the risk of type 2 diabetes (study of 8 randomised trials of n=4,896 participants)(3). However, other studies reported mixed conclusions(8, 9). In those diagnosed with T2DM, supplementation improved markers of insulin resistance(10-12).
Weight loss: There is no clear evidence of the benefit of supplementation with vitamin D on weight loss, change in BMI or body fat(13-15).
Disease/Death Risk: Research suggests vitamin D supplementation can reduce all-cause mortality (data from 80 randomised trials, n= 82,210 participants)(16), but does not reduce cardiovascular morbidity or mortality(16-18).
Testosterone: Vitamin D supplementation (dose 600-4000IU/day) did not significantly improve testosterone or SHBG in men(19-21).
Bone health: In conjunction with calcium supplementation, Vitamin D was able to reduce the risk of hip fractures in men and women. However VitD alone was unable to reach statistical significance(22). Findings also were reinforced included in studies on postmenopausal women who also found improved bone mineral density as a result of combined supplementation(23).
Recommended serving & duration.
Take with meals, or a source of fat,
For studies examining reduction in diabetes risk, at least 2000IU per day was used.
For ideal dose supplementation (varies with country), please refer to ‘Recommended daily allowance (RDA)’ on the nutritional label of supplements.
For moderate supplementation, a daily dose of 1,000–2,000 IU (25–50 μg) of vitamin D3 is sufficient to meet the needs of most people.
Dosages may be higher if you have been found to be deficient (this threshold varies with country). The loading regimen of vitamin D also varies between country.
Safety & tolerability
High doses of vitamin D (3200-4000IU) significantly increase the risk of raised calcium levels – which can lead to: kidney stones, confusion, drowsiness, nausea, vomiting, constipation and fatigue(24).
If there is any doubt whether vitamin D supplementation is right for you, please consult with your healthcare provider.
References:
Tripkovic L, Lambert H, Hart K, Smith CP, Bucca G, Penson S, et al. Comparison of vitamin D2 and vitamin D3 supplementation in raising serum 25-hydroxyvitamin D status: a systematic review and meta-analysis. Am J Clin Nutr. 2012;95(6):1357-64.
Wilson LR, Tripkovic L, Hart KH, Lanham-New SA. Vitamin D deficiency as a public health issue: using vitamin D2 or vitamin D3 in future fortification strategies. Proc Nutr Soc. 2017;76(3):392-9.
Zhang Y, Tan H, Tang J, Li J, Chong W, Hai Y, et al. Effects of Vitamin D Supplementation on Prevention of Type 2 Diabetes in Patients With Prediabetes: A Systematic Review and Meta-analysis. Diabetes Care. 2020;43(7):1650-8.
Sist M, Zou L, Galloway SDR, Rodriguez-Sanchez N. Effects of vitamin D supplementation on maximal strength and power in athletes: a systematic review and meta-analysis of randomized controlled trials. Front Nutr. 2023;10:1163313.
Han Q, Li X, Tan Q, Shao J, Yi M. Effects of vitamin D3 supplementation on serum 25(OH)D concentration and strength in athletes: a systematic review and meta-analysis of randomized controlled trials. J Int Soc Sports Nutr. 2019;16(1):55.
Bislev LS, Grove-Laugesen D, Rejnmark L. Vitamin D and Muscle Health: A Systematic Review and Meta-analysis of Randomized Placebo-Controlled Trials. J Bone Miner Res. 2021;36(9):1651-60.
Abshirini M, Mozaffari H, Kord-Varkaneh H, Omidian M, Kruger MC. The effects of vitamin D supplementation on muscle strength and mobility in postmenopausal women: a systematic review and meta-analysis of randomised controlled trials. J Hum Nutr Diet. 2020;33(2):207-21.
Pittas AG, Kawahara T, Jorde R, Dawson-Hughes B, Vickery EM, Angellotti E, et al. Vitamin D and Risk for Type 2 Diabetes in People With Prediabetes : A Systematic Review and Meta-analysis of Individual Participant Data From 3 Randomized Clinical Trials. Ann Intern Med. 2023;176(3):355-63.
Pieńkowska A, Janicka J, Duda M, Dzwonnik K, Lip K, Mędza A, et al. Controversial Impact of Vitamin D Supplementation on Reducing Insulin Resistance and Prevention of Type 2 Diabetes in Patients with Prediabetes: A Systematic Review. Nutrients. 2023;15(4).
Li X, Liu Y, Zheng Y, Wang P, Zhang Y. The Effect of Vitamin D Supplementation on Glycemic Control in Type 2 Diabetes Patients: A Systematic Review and Meta-Analysis. Nutrients. 2018;10(3).
Wu C, Qiu S, Zhu X, Li L. Vitamin D supplementation and glycemic control in type 2 diabetes patients: A systematic review and meta-analysis. Metabolism. 2017;73:67-76.
Lee CJ, Iyer G, Liu Y, Kalyani RR, Bamba N, Ligon CB, et al. The effect of vitamin D supplementation on glucose metabolism in type 2 diabetes mellitus: A systematic review and meta-analysis of intervention studies. J Diabetes Complications. 2017;31(7):1115-26.
Golzarand M, Hollis BW, Mirmiran P, Wagner CL, Shab-Bidar S. Vitamin D supplementation and body fat mass: a systematic review and meta-analysis. Eur J Clin Nutr. 2018;72(10):1345-57.
Bassatne A, Chakhtoura M, Saad R, Fuleihan GE. Vitamin D supplementation in obesity and during weight loss: A review of randomized controlled trials. Metabolism. 2019;92:193-205.
Perna S. Is Vitamin D Supplementation Useful for Weight Loss Programs? A Systematic Review and Meta-Analysis of Randomized Controlled Trials. Medicina (Kaunas). 2019;55(7).
Ruiz-García A, Pallarés-Carratalá V, Turégano-Yedro M, Torres F, Sapena V, Martin-Gorgojo A, et al. Vitamin D Supplementation and Its Impact on Mortality and Cardiovascular Outcomes: Systematic Review and Meta-Analysis of 80 Randomized Clinical Trials. Nutrients. 2023;15(8).
Angellotti E, D'Alessio D, Dawson-Hughes B, Chu Y, Nelson J, Hu P, et al. Effect of vitamin D supplementation on cardiovascular risk in type 2 diabetes. Clin Nutr. 2019;38(5):2449-53.
Jayedi A, Daneshvar M, Jibril AT, Sluyter JD, Waterhouse M, Romero BD, et al. Serum 25(OH)D Concentration, Vitamin D Supplementation, and Risk of Cardiovascular Disease and Mortality in Patients with Type 2 Diabetes or Prediabetes: a Systematic Review and Dose-Response Meta-Analysis. Am J Clin Nutr. 2023;118(3):697-707.
Hosseini Marnani E, Mollahosseini M, Gheflati A, Ghadiri-Anari A, Nadjarzadeh A. The effect of vitamin D supplementation on the androgenic profile in men: A systematic review and meta-analysis of clinical trials. Andrologia. 2019;51(9):e13343.
Monson NR, Klair N, Patel U, Saxena A, Patel D, Ayesha IE, et al. Association Between Vitamin D Deficiency and Testosterone Levels in Adult Males: A Systematic Review. Cureus. 2023;15(9):e45856.
Adamczewska D, Słowikowska-Hilczer J, Walczak-Jędrzejowska R. The Association between Vitamin D and the Components of Male Fertility: A Systematic Review. Biomedicines. 2022;11(1).
Chakhtoura M, Bacha DS, Gharios C, Ajjour S, Assaad M, Jabbour Y, et al. Vitamin D Supplementation and Fractures in Adults: A Systematic Umbrella Review of Meta-Analyses of Controlled Trials. J Clin Endocrinol Metab. 2022;107(3):882-98.
Liu C, Kuang X, Li K, Guo X, Deng Q, Li D. Effects of combined calcium and vitamin D supplementation on osteoporosis in postmenopausal women: a systematic review and meta-analysis of randomized controlled trials. Food Funct. 2020;11(12):10817-27.
Zittermann A, Trummer C, Theiler-Schwetz V, Pilz S. Long-term supplementation with 3200 to 4000 IU of vitamin D daily and adverse events: a systematic review and meta-analysis of randomized controlled trials. Eur J Nutr. 2023;62(4):1833-44.
