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The ABCs of vitamin D

August 15, 2019 | UCI Health
woman taking vitamin d capsule

It’s hard to believe that in Southern California, where ever-present sunshine provides ample exposure to bone-strengthening vitamin D, many people have too low levels of the vitamin.

UCI Health endocrinologist Dr. Samar Singh says she finds low levels of vitamin D in some 50% of her patients. It may be linked to people spending more time indoors and also to the increasing use of ultraviolet ray-blocking sunscreens recommended by the American Academy of Dermatology.

It is thought to be a worldwide problem — with more than 1 billion people and 42% of Americans estimated to be deficient in vitamin D. The rate goes up for people with darker skin, with 69% of Latinos and 82% of African Americans estimated to have too little vitamin D in their systems.

What is vitamin D?

Known as the sunshine vitamin, vitamin D is produced by the body after exposure to sunlight. In fact, it’s really more than a vitamin. The liver and kidneys convert it into a hormone that is vital for brain function, bone building and other body functions.

Vitamin D increases absorption of calcium, magnesium and phosphate, which is essential for normal bone development and maintenance. Deficiencies can result in problems with bones such as rickets in children and osteoporosis in older adults.

Singh, who is an assistant professor of medicine in the UCI School of Medicine, says studies also are looking at the association between low vitamin D and the incidence of:

“Vitamin D’s importance for bone health is undeniable,” she says. “But the data linking low levels to cancer and heart disease is controversial. We need more research to be convinced of an association.”

How to get more vitamin D

“Sunlight is a large source of vitamin D,” says Singh. “Even with sunscreens that block absorption of ultraviolet rays, you still get some vitamin D. I use the 20-minute rule of daily exposure to sunlight — that’s plenty to get all the vitamin D you need.”

Vitamin D is also found naturally in some foods, including:

In addition, many dairy products, juices and breakfast cereals are fortified with vitamin D. Dietary supplements are available.

“Most people with normal levels don’t need to take supplements if they’re eating a well-balanced diet,” Singh says. “But we recommend supplements for people whose levels are quite low.”

How much should you take?

The recommended daily intake of vitamin D ranges from 600 IU (international units) from age 18 to age 70 and 800 IU after age 70.

But some people have higher risk for developing a deficiency. They include:

  • Breastfed infants since human milk is a poor source of the vitamin
  • Older adults, because as we age, the skin doesn’t make the vitamin as efficiently
  • People with dark skin, because the pigment melanin reduces the skin’s ability to make vitamin D
  • People who live far away from the equator or stay indoors most of the time
  • Obese individuals, because body fat binds with the vitamin preventing it from getting into the blood stream
  • People with health conditions ranging from osteoporosis and chronic kidney or liver diseases to cystic fibrosis and Crohn’s disease

Signs of low vitamin D levels

The problem is that it’s hard to know if you have a vitamin D deficiency without a blood test.

“It’s not very symptomatic, unless it’s affecting bone health,” Singh says. “If you’re experiencing recurrent broken bones, fractures or bone pain, you should see a doctor who can check your levels and make recommendations.”

Other generalized symptoms also may be linked to a vitamin D deficiency, including:

How to increase your levels

Eating more fatty fish and other foods rich in vitamin D, along with fortified dairy and cereals, will help. You can also take it as a supplement, with vitamin D3 being the most effective.

Because vitamin D is fat-soluble, you can take a high dose just once a week. However, too much of it from supplements can be harmful, causing everything from gastrointestinal upsets to kidney damage and even problems with heart rhythm resulting from excess calcium in the blood.

Although vitamin D toxicity is a rare occurrence that results excessive doses, Singh says it’s best to check with your doctor to get the right level of supplementation if you suspect a deficiency.

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