Why Do I Need Vitamin D?


We all know we need vitamin D for its role in bone health, but it has several other important functions. It also aids in immunity, calcium absorption and muscle and cardiovascular function, as well as brain development. There is also ongoing research on vitamin D’s role in muscle function, recovery time and athletic performance.

Since it has so many functions, a lack of vitamin D can be detrimental. Research links low vitamin-D levels to higher mortality rates and increased autoimmune diseases, such as Type 1 diabetes, multiple sclerosis and rheumatoid arthritis. No wonder vitamin D is a hot topic.


The general recommendation for vitamin D in adults is 600-800 IU per day according to the Food and Nutrition Board, which is responsible for the Dietary Reference Intakes (DRIs).

Nearly 50% of the world’s population has insufficient vitamin-D levels, with nearly 1 billion people diagnosed as deficient. There is some debate about what is considered a normal vitamin-D level. The Institute of Medicine defines deficiency as serum levels less than 12 ng/ml, while the Endocrine Society considers levels less than 20 ng/ml as deficient. The Vitamin D Council has the strictest measure, defining levels below 30 ng/ml as deficient. Generally, in healthy individuals, anything less than 20 ng/mL is considered inadequate for bone and overall health and increases the risk of bone fractures.


Good news — you can get all the vitamin D you need from sunshine! Of importance to note, however, vitamin D absorption from sunlight depends on a few factors, including the time of day, where you live, how much skin you expose, air pollution, your skin color and sunscreen use.

The middle of the day is prime time to absorb the most vitamin D from the sun, and research shows that just 10–15 minutes a day is enough. A trick is determining the length of your shadow. If your shadow is longer than you are tall (this usually happens in the winter), you’re likely not able to make sufficient vitamin D. Those with lighter skin can synthesize more vitamin D than those with darker skin pigments, and the closer you live to the equator, the more efficient and easier it is for your body to produce vitamin D. Those who live at northern latitudes have less UVB light available from October to April, which also translates to lower absorption.

While sunscreen is important for our skin health by blocking UV radiation, it hinders vitamin D absorption since UVB is the portion of sunlight that stimulates our skin to produce vitamin D. Wearing sunscreen with SPF 15 or greater can decrease vitamin D3 production by 99%.


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