Vitamin D is a fat-soluble vitamin. It is found in dietary sources, such as fish, eggs, and fortified milk [1]. Furthermore, Vitamin D is produced when the skin is exposed to sunlight [2]. In the United States and in Canada, the importance of Vitamin D for the prevention of osteoporosis is already recognized. A health claim was made on foods that contain Calcium and Vitamin D which may reduce the risk of osteoporosis [3][4]. LOEWI is testing Vitamin D in the form of 25-OH Vitamin D because it has a half-life of 19 days and thus is better suited to judge the long-term status of Vitamin D than 1-25-OH Vitamin D, which has a half-life of just a few hours.

National Nutrition Study

  • 82% of all men do not reach the recommended daily allowance of Vitamin D.
  • 91% of all women do not reach the recommended daily allowance of Vitamin D [10].

Function of Vitamin D

Vitamin D regulates the balance of minerals in the body. When it comes to the mineralization of bones, Vitamin D helps to better absorb nutritional Calcium in the gut. In that case, it functions as a hormone [5] [6] [7] [8].
The vitamin plays an important role in both the innate and the acquired immune system [5] [6] [8].
An analysis of clinical research suggests that Vitamin D3 reduces the risk of caries by 49% in infants, children, and adolescents [9].
Vitamin D influences the endocrine system and, therefore, the secretion of insulin in the body [5].

Deficiency Symptoms

Population research has found that low Vitamin D levels are associated with a bad cognitive performance and a cognitive decline compared to high Vitamin D levels in healthy adults [13] [14].
Clinical research suggests that Vitamin D may increase hip muscle strength in adults who are deficient in Vitamin D at baseline [11]. Another analysis of clinical research suggests that Vitamin D may increase the lower body strength, particularly in patients who are deficient in Vitamin D at baseline [12].
Population research shows that people with lower Vitamin D levels are significantly more likely to be obese compared to people with higher Vitamin D levels [15].
A Vitamin D deficiency can lead to osteomalacia. Typical signs of osteomalacia are muscle weakness and muscle pain [5] [6].
There is a correlation between bone density, bone fractures, and Vitamin D blood levels. The lower the Vitamin D levels are, the lower is the bone density and the higher is the risk for bone fractures [5] [6].
A deficiency in Vitamin D can subsequently cause a deficiency of Calcium [5] [8].

Surplus of Vitamin D

A surplus of Vitamin D (hypervitaminosis) can only be caused by excessive supplementation [5].
The symptoms can be diverse, like nausea, diarrhea, dizziness, and muscle weakness [5].
Furthermore, it can case a disturbance of the electrolyte system, which in turn can cause a surplus of Calcium [5].

[1] Food and Nutrition Board, Institute of Medicine. Dietary Reference Intakes for Calcium, Phosphorus, Magnesium, Vitamin D, and Fluoride. Washington, DC: National Academy Press, 1999. Available at:

[2] Holick MF. Vitamin D: importance in the prevention of cancers, type 1 diabetes, heart disease, and osteoporosis. Am J Clin Nutr 2004;79:362-71.. (Abstract:

[3] L’Abbe MR, Whiting SJ, Hanley DA. The Canadian health claim for calcium, vitamin D and osteoporosis. J Am Coll Nutr 2004;23:303-8. (Abstract:

[4] Food and Drug Administration, HHS. Food labeling: health claims; calcium and osteoporosis, and calcium, vitamin D, and osteoporosis. Final rule. Fed Regist. 2008;73(189):56477-87. (Abstract:

[5] Koula-Jenik, H., Miko M., Kraft M., Schulz R., Leitfaden Ernährungsmedizin.  Elsevier,Urban&Fischer Verlag 2013;p.31-33

[6] Biesalski HK., Muniz K., Vitamine und Minerale: Indikation, Diagnostik, Therapie. Thieme Verlag 2017; p.39

[7] Wibusch N, Hofmann P, Förster H, Hörtnagl HLedl-Kurkowski E, Pokan R, Kompendium der Sportmedizin Physiologie, Innere Medizin und Pädiatrie. Springer-Verlag 2016; p. 349

[8] Christoph Raschka, Stephanie Ruf, Sport und Ernährung: Wissenschaftlich basierte Empfehlungen, Tipps und Ernährungspläne für die Praxis. Georg Thieme Verlag 2015; p.121-122

[9] Hujoel, P. P. Vitamin D and dental caries in controlled clinical trials: systematic review and meta-analysis. Nutr Rev. 2013;71(2):88-97. (Abstract:

[10] Max-Rubner-Institut, Bundesministerium für Ernährung, Landwirtschaft und

Verbraucherschutz, Hrsg. Nationale Verzehrstudie II. Karlsruhe: MRI; 2008

[11] Stockton, K. A., Mengersen, K., Paratz, J. D., Kandiah, D., and Bennell, K. L. Effect of vitamin D supplementation on muscle strength: a systematic review and meta-analysis. Osteoporos.Int 2011;22(3):859-871. (Abstract:

[12] Beaudart C, Buckinx F, Rabenda V, Gillain S, Cavalier E, Slomian J, Petermans J, Reginster JY, Bruyère O. The effects of vitamin D on skeletal muscle strength, muscle mass, and muscle power: a systematic review and meta-analysis of randomized controlled trials. J Clin Endocrinol Metab. 2014 Nov;99(11):4336-45. (Abstract:

[13] Balion, C., Griffith, L. E., Strifler, L., Henderson, M., Patterson, C., Heckman, G., Llewellyn, D. J., and Raina, P. Vitamin D, cognition, and dementia: a systematic review and meta-analysis. Neurology 9-25-2012;79(13):1397-1405. (Abstract:

[14] Goodwill AM, Szoeke C. A systematic review and meta-analysis of the effect of low vitamin D on cognition. J Am Geriatr Soc. 2017;65(10):2161-2168. (Abstract:

[15] Martins D, Wolf M, Pan D, et al. Prevalence of cardiovascular risk factors and the serum levels of 25-hydroxyvitamin D in the United States. Arch Intern Med 2007;167:1159-65. (Abstract:


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