Do I Need a Vitamin D Blood Test?

A: The importance of sufficient vitamin D for bone health has a long history. In the past few decades, several studies have suggested that vitamin D might have other health benefits as well.

For instance, observational studies have found an association between low levels of vitamin D and heart disease, diabetes, and certain cancers. While people with these diseases may be more likely to have lower levels of vitamin D in their blood when tested, no studies have shown that insufficient vitamin D actually causes the diseases.

When all these studies were examined by a panel of experts sponsored by the U.S. Preventive Services Task Force, the experts concluded that the evidence did not support routine screening for vitamin D deficiency.

Their main reasoning was that there is no consensus regarding the optimal level needed to keep bones healthy. For instance, traditional guidelines state that vitamin D levels should be at least 20 nanograms per milliliter (ng/mL). (A blood test measures a form of the vitamin known as 25-hydroxyvitamin D.) But some experts say this amount is too low and the level should be 30 ng/mL or higher.

Most experts acknowledge that true vitamin D deficiency is below 12 ng/mL, but this is quite uncommon. People who might have a level this low and need regular vitamin D testing include those who:

• have a gastrointestinal condition like celiac disease that decreases the ability to absorb vitamin D
• are malnourished
• regularly take medication that interferes with vitamin D activity, such as an oral corticosteroid (such as prednisone) or certain anti-seizure medications

In addition, everyone who has been told they may have thin bones (either osteopenia or osteoporosis) or a fragility fracture (broken bones that occur from minimal trauma) should get their vitamin D levels checked routinely.

The good news is that getting enough vitamin D is easy for most people. Adults up to age 70 should get 600 international units (IU) per day, and those older than this should get 800 IU.

You are probably getting enough vitamin D from your sun exposure if you have no other possible reasons for a low level. Experts vary on their recommended sun time. For fair skinned people, about 15 minutes in midday a few times a week will usually be sufficient. Darker skinned people need more than 30 minutes most days of the week.

Good food and beverage sources of vitamin D are swordfish, salmon and tuna, and vitamin D-fortified orange juice and milk. For men who think they don’t get enough of vitamin D, a daily 1,000 IU vitamin D3 supplement is quite safe.

Howard LeWine, M.D., is an internist at Brigham and Women’s Hospital in Boston and assistant professor at Harvard Medical School. For additional consumer health information, please visit www.health.harvard.edu.

©2023 Harvard University. For terms of use, please see https://www.health.harvard.edu/terms-of-use. Distributed by Tribune Content Agency, LLC.

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