What is vitamin D?
Vitamin D, or calciferol, is a fat-soluble vitamin essential for many body functions. It is normally obtained naturally from foods, fortified foods (foods that had micronutrients added to them), and dietary supplements (such as vitamin D drops). It is also made internally through the absorption of sunlight. More specifically, ultraviolet (UV) rays from the sun initiate vitamin D synthesis.
Functions of vitamin D
Vitamin D assists calcium absorption in the gastrointestinal tract to maintain normal calcium levels and bone mineralization (the process of deposition of minerals on the bone matrix for the development of bone). It is also required for bone growth and remodeling (to protect the structural integrity of the skeletal system and to reasorb old or damaged bone to later deposit, respectively).
Other than calcium absorption, vitamin D also plays a role in modulating certain cell processes like cell growth, neuromuscular and immune function, and glucose metabolism. Vitamin D regulates over 1000 cells, which controls processes such as cell proliferation, differentiation, and apoptosis.
Evidence-based benefits of vitamin D
Decreased risk of fractures and osteoporosis (low bone mass and structural deterioration of bone tissue) in older adults
Preserves muscle fibers, therefore increasing muscle strength to lower risk of falls
May reduce risk of cancer and cancer deaths
Lowered risk of cardiovascular disease and increased heart health
Reduces overall mortality rate
Health risks of excessive vitamin D
Too much vitamin D is toxic. Since vitamin D promotes calcium absorption in the gut, excessive vitamin D results in hypercalcemia (too much calcium in the blood). In severe cases, excessive vitamin D (vitamin D toxicity) can lead to renal failure, calcification of soft tissues (including in coronary vessels and heart valves), cardiac arrhythmias, and even death.
Sources of vitamin D
Foods: the best include fatty fish and fish liver oils. Lower levels can be found in egg yolks, cheese, and beef liver. Moreover, many foods are fortified with vitamin D supplements (such as dairy products and cereals).
Supplements: the most common supplements include those with vitamin D2 and D3. Experts cite vitamin D3 is the optimal form because it is naturally produced in the body and found in most natural food sources of vitamin D.
Sunlight: vitamin D is produced naturally by UVB light, where a steroid called 7-dehydrocholesterol is broken down by the sun’s UVB light.
For more information, refer to the consumer vitamin D fact sheet by the National Institutes of Health.
Works Cited
"Vitamin D." Harvard T.H. Chan, President and Fellows of Harvard College,
www.hsph.harvard.edu/nutritionsource/vitamin-d/. Accessed 30 Apr. 2024.
"Vitamin D." Mayoclinic, Mayo Foundation for Medical Education and Research, 10 Aug.
2023, www.mayoclinic.org/drugs-supplements-vitamin-d/art-20363792. Accessed 1
May 2024.
"Vitamin D." National Institutes of Health, ods.od.nih.gov/factsheets/VitaminD
HealthProfessional/. Accessed 1 May 2024.
Ware, Megan. "What is vitamin D and why does the body need it?" MedicalNewsToday,
www.medicalnewstoday.com/articles/161618#role-of-vitamin-d. Accessed 1 May 2024. Assessed and Endorsed by the MedReport Medical Review Board