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Get your Vitamin D from food, sunlight

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Sun vitamin D

Human skin can make large amounts of Vitamin D when exposed to UVB radiation from the sun.

SIOUX CITY | Muscles need Vitamin D to move.

Nerves need it to carry messages between the brain and every body part.

The immune system needs vitamin D to fight off invading bacteria and viruses.

People who get too little vitamin D may develop soft, thin, brittle bones, a condition known as rickets in children and osteomalacia in adults.

Although it can impact various systems in the body, the main system Vitamin D supports is the musculoskeletal system.

Steven Joyce, a Mercy Medical Center Internal Medicine & Pediatrics physician, said researchers have examined Vitamin D's effects on cardiovascular and memory health, but he said those studies haven't proven that Vitamin D particularly benefits those body systems.

So how much Vitamin D do we need to stay healthy and what's the best way to get it?

"Although we know that calcium and Vitamin D are needed for good bone health, the exact dosages and how to achieve that best are not well known," said Joyce, who said people get most of the Vitamin D that they need from food and sunlight.

Fatty fish such as salmon and tuna are among the best sources of the fat-soluble vitamin that promotes calcium absorption in the gut, according to the National Institutes of Health. Cheese, egg yolks and mushrooms also contain some. Almost all of the U.S. milk supply is fortified with 400 IU of Vitamin D per quart and Vitamin D has also been added to many breakfast cereals.

Human skin can make large amounts of Vitamin D when exposed to UV-B radiation from the sun. The sun's energy turns a chemical in your skin into Vitamin D3, which is carried to your liver and then your kidneys to transform it to active Vitamin D.

Indy Chabra, a dermatologist at Midlands Clinic in Dakota Dunes, said the same UV-B radiation that is essential for vitamin D synthesis also increases skin cancer risk by causing DNA damage.

"The key is to obtain enough sun exposure to produce vitamin D while not increasing one's risk of skin cancer or to ingest vitamin D from diet or vitamin D supplements," he said.

Infants born during wintertime, Joyce said, may benefit from Vitamin D supplementation, as they're likely not going to get any sunlight. He said older adults are also at increased risk for developing vitamin D insufficiency, because as they age skin doesn't synthesize vitamin D as efficiently.

"We live in the Northern Hemisphere, where -- especially from November to February -- we don't get a lot of direct sunlight," he said. "That's where Vitamin D supplementation comes into play."

Chabra said the amount of sun exposure required to produce sufficient vitamin D in the skin is dependent on multiple factors, including a person's skin color, areas of the body exposed to the skin, degree of cloud cover, time of the year and distance from the equator. Wearing sunscreen will prevent Vitamin D production.

By limiting your sun exposure to time sufficient for vitamin D production, Chabra said you can generate enough vitamin D without greatly increasing your risk for skin cancer.

For example, he said a Caucasian person with skin of average skin color living in Boston (the same latitude as Sioux City) needs to expose 25 percent of their body surface area to the sun for 3 to 8 minutes at noon to synthesize 400 International units (IU) of Vitamin D from April to October.

"In the US, 600 IU of Vitamin D is the recommended daily Vitamin D intake for adults 1-70 years of age, and 800 IU for people older than 70 years of age," he said.

Although overdosing on Vitamin D is rare, Joyce said it's possible. Poor appetite, nausea and vomiting, weakness, frequent urination and kidney problems are consequences of Vitamin D toxicity. He said people who take Vitamin D supplements need to be cautious. Supplements aren't regulated by the U.S. Food and Drug Administration.

"If you take too much, your body doesn't get rid of it in urine. It stores it in the fat and the liver, so you can get issues if you overdose on them," he said.

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