Vitamin D was originally recognized as a fat soluble vitamin needed in small amounts for the metabolism of calcium and phosphate. It is found in significant amounts in oily fish and in small amounts in other ingredients of the Western diet, such as egg yolks, cheese, butter, orange juice and mushrooms. Vitamin D is also generated in large quantities on the skin under the sunlight (UVB irradiance). Vitamin D enters the circulation and binds to specific proteins, which facilitate its transport to the different body tissues. Nowadays, it is well known that vitamin D acts as a hormone on the cells of the immune system generating anti-inflammatory and immunoregulatory effects. Optimal vitamin D intake and its status are important for the overall health and vitamin D deficiency or insufficiency as a global health problem has been associated with many acute and chronic illnesses.
Vitamin D for Healthy Bone Structure
Chronic Vitamin D deficiency is associated with rickets and classic skeletal abnormalities, such as deformities of the legs. Vitamin D deficiency in both children and adults causes a decrease in the efficiency of intestinal calcium absorption, resulting in a decline of ionized calcium concentration in the serum. The parathyroid glands secrete parathyroid hormone (PTH) into the bloodstream in response to low blood calcium levels. PTH acts to raise blood calcium levels by:
Stimulating the kidneys to convert vitamin D from the inactive form to the active form, which travels to the small intestine to increase the absorption of calcium from food.- Promoting the release of calcium from the bones into the circulation. This process results in a decrease in bone mass that can precipitate and exacerbate osteopenia (low bone mass) and osteoporosis in both children and adults.
- Increasing the reabsorption of calcium and decreasing the reabsorption of phosphate in the kidneys, causing a lowering of the blood phosphorus level. The resulting decrease in mineral bone density causes osteomalacia.
Vitamin D and Immunomodulation
Vitamin D sufficiency is critical in immune system health. So far, more than 30 beneficial effects of vitamin D on the immune system have been reported.
- Vitamin D has a role in the production, maturation and secretion of antimicrobial agents, reducing the risk of infectious diseases.
- Vitamin D regulates immune responses associated with autoimmunity. Its sufficiency may inhibit or improve such conditions in genetically susceptible individuals. Its deficiency has been largely documented in various autoimmune diseases, such as rheumatoid arthritis (RA), systemic lupus erythromatosus (SLE), multiple sclerosis (MS), type 1 diabetes mellitus, inflammatory bowel diseases, autoimmune thyroid diseases (e.g. Grave’s disease and Hashimoto’s thyroiditis), autoimmune hepatitis and many others.
- Vitamin D has a major role in controlling immune responses associated with inflammation. Its deficiency may be a risk factor for sepsis and inflammatory disorders.
Ongoing Studies on Vitamin D
Since vitamin D receptors are distributed across various human tissues there is some evidence from various ongoing studies suggesting that sufficient levels of vitamin D may have a beneficial effect on:
- Fertility
- Pregnancy and Lactation
- Cancer
- The Cardiovascular System
- Mortality
- Alzheimer’s Disease
References:
- Antico A. et al. Can supplementation with vitamin D reduce the risk or modify the course of autoimmune diseases? A systematic review of the literature. Autoimmunity Reviews 12(2012): 127-136
- Bjorklund G. et al. The Role of Vitamin D in the Immune System as a Pro-Survival Molecule. Clinical Therapeutics, Volume 1, 2017: 1-23
- Barcellini W. et al. Reduced 25-OH vitamin D in patients with autoimmune cytopenias, clinical correlations and literature review. Autoimmunity Reviews 15(2016): 770-775
- Holick M. F. et al. Vitamin D effects on musculoskeletal health, immunity, autoimmunity, cardiovascular disease, cancer, fertility, pregnancy, dementia and mortality – A review of recent evidence. Autoimmunity Reviews 12(2013): 976-989
- Castafleda S. et al. Vitamin D and Autoimmune Rheumatic Diseases. Rheumatol Clin. 2016:12(6): 356-364
- Bogdanos D. P. et al. Vitamin D in autoimmune liver disease. Clinics and Research in Hepatology and Gastroenterology(2013)37: 535-545
- D’Aurizio F. et al. Is vitamin D a player or not in the pathophysiology of autoimmune thyroid diseases? Autoimmunity Reviews 14(2015): 363-369