It definitely feels like summer outside, and while the sun is out and shining, it's important to talk about a vitamin we actually get more of by spending time outside - Vitamin D!
Vitamin D comes in 2 forms: D2 (ergocalciferol) and D3 (cholecalciferol), and can be found in foods, supplements, and we get it from sun exposure.
Vitamin D is often known for its important role in bone development and maintenance and deficiency has serious health consequences for bone health. Rickets in children and osteomalacia in adults are the two bone-related diseases caused by severe vitamin D deficiency. Severe deficiency and rickets has become rare in children after milk starting getting fortified with Vitamin D in the 1930's.
Vitamin D plays other roles beyond bone health, though - it has functions in gene expression, muscular function, immunity, wound healing, and cardiovascular health.
Most people are getting enough Vitamin D to prevent severe deficiency and bone health issues, but modest deficiency is common, and some people who are more likely to have a vitamin D deficiency include:- People who spend a lot of time indoors during the day
- People who cover their skin or wear sunscreen at all times when outside
- People with darker skin
- People who live in the northern states of the U.S. or Canada (fewer hours of sunlight, and further from the equator)
- Older people
- People who are obese
Very few foods are naturally high in vitamin D.
On the last blog, we mentioned that vitamin D will be listed on the new Nutrition Facts Label in the future because people really aren't getting enough of it. Many foods, such as milk, orange juice, yogurt, and ready-to-eat cereals are actually fortified with vitamin D, meaning it is added during processing, but the foods that are naturally high in vitamin D are rare.
Those naturally vitamin-D rich foods include fatty fish (salmon, mackeral, tuna), fish liver oils, egg yolks, beef liver, cheese, and some muschrooms.
For many people, sun exposure is their primary source of Vitamin D.
Ultravoilet-B (UVB) radiation stimulates vitamin D3 to be produced in the epidermis of the skin, but factors such as season, time of day, cloud cover, smog, skin color and sunscreen use effect vitamin D synthesis from UV exposure.
Some vitamin D researchers have recommended exposing face, arms, legs or back without sunscreen for 5-30 minutes during peak sunlight hours (between 10AM - 3PM) several times per week. This doesn't mean tanning or burning your skin, and less time outdoors is needed in the summer, and this goes against the the Skin Cancer Foundation, who cautions against this sun exposure in order to get Vitamin D - using sunscreen, covering up and limiting sun exposure and UV radiation from tanning beds is important for preventing skin cancer.
At the end of the day, you can always get Vitamin D through vitamin D-fortified foods and vitamins.
A blood test for serum concentration of 25(OH)D is the best indicator of vitamin D status, and the Institute of Medicine claims that:
- People are at risk for deficiency if serum 25(OH)D levels are <30 li="" ml="" ng="" nmol="">
- Levels ≥50 nmol/L (≥20 ng/mL) are suffient for good bone healthy for almost all individuals
Vitamin D for Athletes
It is estimated that about 1 billion people of all ages are vitamin D insufficient or deficient, and athletes aren't immune to vitamin D deficiency. Studies examining vitamin D status in NFL players have shown that a significant number of players had deficient or insufficient vitamin D levels (especially amongst African American football players), making vitamin D intake a focus for many teams.Many collegiate and professional sports teams are supplementing their athletes with vitamin D, and providing foods such as fortified cereals to their diets to prevent Vitamin D insuffiency.
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