Vitamin D is a fat-soluble vitamin that is essential to many of the body’s processes. Whether supporting immune, musculoskeletal, or brain health, Vitamin D is definitely a valuable player in maintaining overall health and wellness.
The History of Vitamin D
But to really understand Vitamin D, we need to go back to the early 1600s when rickets in children and osteomalacia in adults were first described. Coinciding with the Industrial Revolution, a combination of indoor occupations, smog, and decreased dietary calcium intake may have contributed to Vitamin D deficiency. Without sufficient Vitamin D, calcium is not properly absorbed, and bones become soft, weak, and deformed.  
Centuries later in Great Britain, Sir Edward Mellanby, a biochemist, was concerned with the incidence of rickets in the United Kingdom and hypothesized that the disease was caused by a dietary deficiency. To test this, he fed dogs a strict diet of oatmeal (the main diet of Scottish folk who had the highest incidence of rickets at the time) and kept them away from sunlight. Once the dogs developed rickets, he noticed that they could be cured with cod liver oil. To determine whether it was Vitamin A or another vitamin that was responsible, Professor Elmer McCollum of Johns Hopkins University decided to conduct an experiment of his own. By destroying Vitamin A from the cod liver oil, McCollum identified that a new vitamin, which they called Vitamin D, was the true component responsible for curing the disease. 
Eventually, dietary supplementation and fortification of food and infant formula led to a decrease in nutritional rickets. However, Vitamin D deficiency prevails. Social and cultural shifts including preferences for fair skin, a sedentary lifestyle, health concerns over skin cancer, time constraints, and many other factors have led to decreased ultraviolet B (UVB) exposure.
Who is susceptible to deficiency?
A few characteristics can make a person more susceptible to deficiency. Living in regions with low sunlight such as northern latitudes, especially during the winter months, can limit the amount of natural Vitamin D that your body synthesizes, even if you spend time outside. People with darker skin tones are prone to being deficient because melanin inhibits Vitamin D synthesis. As people age, the skin becomes less efficient at synthesizing Vitamin D. Additionally, since Vitamin D is a fat-soluble vitamin, people who are overweight or obese may have Vitamin D sequestered in fat cells, which results in lower circulating Vitamin D concentrations. Ultimately, geographic location, melanin levels, age, and obesity status, in addition to diet, disorders, and medication, could all potentially impact Vitamin D availability.
So if Vitamin D is so important, how can we prevent deficiency?
Chances are, when you think about Vitamin D, you think of sunlight. Spending about 10-30 minutes in the sun a few times a week, exposing your skin to the UVB rays, can help your body naturally synthesize Vitamin D. The amount of time needed varies based on factors such as your skin type, geographic location, and UV index. If you live in an area without as much sunlight, you can try a UV lamp. Diet is another way to obtain Vitamin D. Fatty fish such as salmon, mackerel, and trout are excellent sources. Egg yolks and mushrooms also contain some, but many foods nowadays such as milk, orange juice, breakfast cereals, and yogurt are often fortified with Vitamin D. Supplements are a convenient, accessible option if you have dietary restrictions or limited sun exposure. If you are concerned about your Vitamin D levels or have specific health conditions, it is advisable to consult with a healthcare professional. They can assess your Vitamin D status and recommend appropriate treatment options based on your individual needs. 
Disclaimer: If you have any medical questions or concerns, please talk to your healthcare provider. The articles on the SiPhox Health Hub are underpinned by peer-reviewed research and information drawn from medical societies and governmental agencies. However, they are not a substitute for professional medical advice, diagnosis or treatment.
|1||Deluca HF. History of the discovery of vitamin D and its active metabolites. Bonekey Rep. 2014 Jan 8;3:479.|
|2||“Vitamin D.” Mayo Clinic, Mayo Foundation for Medical Education and Research, 10 Aug. 2023. https://www.mayoclinic.org/drugs-supplements-vitamin-d/art-20363792|
|3||“Vitamin D.” The Nutrition Source, 7 Mar. 2023. https://www.hsph.harvard.edu/nutritionsource/vitamin-d/|
|4||Wheeler BJ, Snoddy AME, Munns C, Simm P, Siafarikas A, Jefferies C. A Brief History of Nutritional Rickets. Front Endocrinol (Lausanne). 2019 Nov 14;10:795. doi: 10.3389/fendo.2019.00795. PMID: 31798536; PMCID: PMC6867964.|