Vitamin D is an essential substance for the body to grow and develop regularly. The body needs vitamin D to absorb calcium. (1) Normal serum vitamin D levels determine the absorption of 30% of dietary calcium and more than 60-80% during periods of growth, due to the high demand for calcium. Without enough vitamin D, your body can’t produce enough of the hormone calcitriol (known as the “active vitamin D”). This, in turn, leads to insufficient calcium absorption from the diet. Lack of vitamin D weakens existing bone and prevents the formation of strong, new bone. Low vitamin D levels may lead to clinical manifestations, including bone pain, muscle weakness, falls, low bone mass, and fractures, with subsequent diagnoses of osteomalacia, osteoporosis, and myopathy. (2) Vitamin D also increases the absorption of phosphorus. (3) Phosphorus plays an important role in bone health and in the structure of nucleic acids and cell membranes. It is also involved in the body’s energy production. 

This is not the only effect vitamin D has on natural growth. Vitamin D increases circulating insulin-like growth factor-1(IGF-1) in adults. (4) A significant increase in serum IGF-1 was also noted in response to vitamin D in small cohorts of children. (5) In a group that treated 7,000IU of vitamin D showed IGF-1 levels significantly increased by 31.3±36.7 ng/ml (P=0.01). (4) As a result, a better vitamin D status may ease the achievement of normal IGF1 values in GHD (Growth Hormone Deficiency). 

In addition to helping calcium absorption and secreting insulin-like growth factor-1 (IGF-1), vitamin D plays an important role in children’s health. Vitamin D deficiency is linked to high blood pressure in children. A study from 2018 found a possible connection between low vitamin D levels and stiffness in the arterial walls of children. (6) The American Academy of Allergy Asthma and Immunology (AAAAI) suggests a connection between low vitamin D exposure and an increased risk of allergic sensitization. (7) Furthermore, vitamin D may enhance the anti-inflammatory effects of glucocorticoids. This benefit makes it potentially useful for supportive therapy for people with steroid-resistant asthma. (8) 

Vitamin D can modulate innate and adaptive immune responses. (9) Deficiency in vitamin D is associated with increased autoimmunity as well as increased susceptibility to infection. Vitamin D is important for improved resistance against certain diseases. Vitamin D had a protective effect against the influenza virus, helping to reduce the likelihood of developing the flu and decreasing the chance of developing heart disease. (10, 11) Vitamin D also plays an important role in regulating mood and warding off depression. In one study, scientists found that people with depression who received vitamin D supplements noticed an improvement in their symptoms. (12) In another study of people with fibromyalgia, which is a disorder characterized by widespread musculoskeletal pain accompanied by fatigue, sleep, memory and mood issues, researchers found vitamin D deficiency was more common in those who were also experiencing anxiety and depression. (13) 

Recent data suggest that vitamin D supplementation may also reduce the severity of atopic dermatitis. (8) In addition, Vitamin D may also help prevent obesity. In one study, people taking daily calcium and vitamin D supplement were able to lose more weight than subjects taking a placebo supplement. (14) The scientists explained that the additional calcium and vitamin D had an appetite-suppressing effect. 

References: 

1. Calcium and Vitamin D: Important at Every Age, National Institute of Arthritis and Musculoskeletal and Skin Diseases 

2. ANDREA N. JONES, KAREN E. HANSEN. Recognizing the musculoskeletal manifestations of vitamin D deficiency J Musculoskelet Med. 2009 Oct; 26 (10): 389-396. 

3. DeLuca HF. The metabolism and functions of vitamin D. Adv Exp Med Biol. 1986; 196:361-75. 

4. Ameri P, Giusti A, Boschetti M, Bovio M, Teti C, Leoncini G, Ferone D, Murialdo G, Minuto F. Vitamin D increases circulating IGF1 in adults: potential implication for the treatment of GH deficiency. Eur J Endocrinol. 2013 Oct 21;169 (6): 767-72. 

5. Bereket A, Cesur Y, Özkan B, Adal E, Turan S, Onan SH, Döneray H, Akçay T, Haklar G. Circulating insulin-like growth factor binding protein-4 (IGFBP-4) is not regulated by parathyroid hormone and vitamin D in vivo: evidence from children with rickets. J Clin Res Pediatr Endocrinol. 2010; 2 (1): 17-20. doi: 10.4274/jcrpe.v2i1.17. Epub 2010 Feb 2 

6. Skrzypczyk P, Dziedzic-Jankowska K, Ofiara, A, Szyszka M, Panczyk-Tomaszewska M. VITAMIN D AND BLOOD PRESSURE PARAMETERS IN CHILDREN AND ADOLESCENTS WITH ARTERIAL HYPERTENSION Journal of Hypertension. 2018 Jun; 36:e250 

7. Vitamin D and Food Allergy, American Academy of Allergy Asthma & Immunology; Retrieved from: https://www.aaaai.org/conditions-and-treatments/library/allergy-library/vitamin-d-food-allergy

8. Benetti C, Comberiati P, Capristo C, Boner AL, Peroni DG. Therapeutic Effects of Vitamin D in Asthma and Allergy. Mini Rev Med Chem. 2015; 15 (11): 935-43. 

9. Cynthia Aranow. Vitamin D and the Immune System J Investig Med. 2001 Aug; 59 (6): 881-886. 

10. Beata M. Gruber-Bzura. Vitamin D and Influenza—Prevention or Therapy? Int J Mol Sci. 2018 Aug; 19 (8): 2419. 

11. Urashima M, Segawa T, Okazaki M, Kurihara M, Wada Y, Ida H. Randomized trial of vitamin D supplementation to prevent seasonal influenza A in schoolchildren. Am J Clin Nutr. 2010 May; 91 (5): 1255-60. 

12. Jorde R, Sneve M, Figenschau Y, Svartberg J, Waterloo K. Effects of vitamin D supplementation on symptoms of depression in overweight and obese subjects: randomized double blind trial. J Intern Med. 2008 Dec; 264 (6): 599-609. 

13. Armstrong DJ, Meenagh GK, Bickle I, Lee AS, Curran ES, Finch MB. Vitamin D deficiency is associated with anxiety and depression in fibromyalgia. Clin Rheumatol. 2007 Apr; 26 (4): 551-4. 

14. Major GC, Alarie FP, Doré J, Tremblay A. Calcium plus vitamin D supplementation and fat mass loss in female very low-calcium consumers: potential link with a calcium-specific appetite control. Br J Nutr. 2009 Mar; 101 (5): 659-63.