Vitamin D: What Is It and Why Do We Need It?

by Jennifer Novakovich

Many of us already know that vitamin D is critical for bone health, but recently its importance has been extended to just about all areas of good health. A deficiency is now also related to many chronic disorders including mental illness, heart disease, infection, autoimmune diseases, cancer, rickets, obesity, inflammation, diabetes, and so on. In a recent study in a Boston hospital, about 42% of the adolescent patients that were examined had a deficiency and an estimated 1 billion people world-wide aren't getting enough. Clearly the prevalence of vitamin D is high, so how do you compare?

What is vitamin D and what does it do? Vitamin D is a fat soluble vitamin that can come in two forms, D2 (ergocalceiferol) from plants and D3 (cholecalciferol) from animals. While there are two forms, vitamin D3 is the only one that is naturally seen in humans. Vitamin D can either be consumed (e.g. in egg yolks, oily fish, and fortified foods, or for vegans, mushrooms), although dietary sources are typically not sufficient, or produced by our skin following the sun’s (UV light) action on a compound called 7-dehydrocholesterol. Both dietary and endogenous vitamin D will be converted to 25-hydroxycholecalciferol (25(OH)D3) in the liver and then to the active 1,25-dihydroxycholecalciferol (1,25 (OH)2D3) form, calcitriol, in the kidney. Calcitriol acts as a hormone and regulates blood calcium and phosphate to promote bone remodeling and adequate blood calcium. Vitamin D is also vital for the absorption of calcium in our intestines, which is why a calcium supplement should be paired with vitamin D (and K2!).

What are some of the effects from a vitamin D deficiency? Vitamin D is an important neurosteroid hormone, playing a role in neuroplasticity and neuroimmunomodulation. Vitamin D deficiencies are associated with many mental illnesses including autism, Parkinson's, depression, and schizophrenia. Deficiencies are also associated with obesity and diabetes. Clinical studies have consistently shown low vitamin D status in obese individuals. Moreover, obesity results in lower vitamin D availability from fat tissues. Lastly, vitamin D is a factor for inflammation and may be important in the treatment of inflammatory related diseases such as heart disease, arthritis, and even cancer.

Issues with vitamin D deficiencies also extend to athletes and their performance. Muscle biopsies in individuals with a deficiency show major changes to muscle fibers (predominantly type 2 fibers). Vitamin D explains seasonal variability in performance, where studies consistently show improved performance at the tail end of the summer and then a decline through winter months despite consistent training year long. Recently, studies have shown a direct relationship between blood vitamin D levels and power, force, velocity, grip strength, jump height, overall strength, and overall performance. Thankfully the deleterious changes from a deficiency are reversible and athletes who are deficient in vitamin D may see performance gains through supplementation

Again, dietary vitamin D isn't typically sufficient but the amount of sunlight necessary is quite controversial due to the fact that sunlight undoubtedly causes DNA damage in skin cells, which is a risk factor for skin cancer. As a result, many people follow strict sun protection regimes—excessive sunscreen, less time outside, more clothing—which has added to the high rates of vitamin D deficiencies (characterized by blood 25(OH)D3 levels at 50nmol/l). High risk individuals are those who spend most of their time indoors, like people who live in nursing homes, or in most of us during the wintertime. Since our main source of vitamin D is through our skin, supplementation, especially throughout the wintertime, may be wise.

Adequate vitamin D can be achieved by time spent outside with exposed skin. In the summer, a time of 6–8 minutes may be enough, while in the winter, times increase to 7–50 minutes or so depending on the latitude. Personally, exposed skin during the wintertime is...uncomfortable; supplementation is definitely the easiest way to go in cold months. Supplementation in individuals who typically stay inside or follow strict sun protection regimes is vital to maintain adequate vitamin D. In individuals with a pre-existing deficiency, one dose of 50000IU once per week for 8 weeks has been shown to efficiently treat a vitamin D deficiency. When a deficiency is not present, an intake of 1000-2000 IU/day of vitamin D is recommended to ensure an adequate source. Whether supplementing or not, enough vitamin D is critical; it's clear to see how important vitamin D is.

And that marks the end of my article. Vitamin D is crucial for just about all areas of health and reduces risks for many chronic diseases, fights obesity, and has even been shown to boost athletic performance. Unfortunately, the majority of the population isn't getting nearly enough, largely due to a lack of awareness on the importance of this vitamin. Hopefully you now have a better understanding of the importance of vitamin D and how to get enough.

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Mezza T,Muscogiuri G, Sorice G, Prioletta A,Salomone E,Pontecorvi A, Giaccari A. (2012) Vitamin D Deficiency: A New Risk Factor for Type 2 Diabetes? DOI:10.1159/000342771

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Sinha A, Cheetham T, Pearce, S. (2013) Prevention and Treatment of Vitamin D Deficiency. DOI:10.1007/s00223-012-9663-9.

See this and other articles on Jennifer Novakovich’s website JennovaFoodBlog.com