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Vitamin D Levels in the U.S. Population are Getting a Little Better!

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Live well

Friday, Sep 22, 2017

 

Vitamin D Levels in the U.S. Population are Getting a Little Better!

Because vitamin D can be formed in the skin upon exposure to sunlight, it is known as “the sunshine vitamin.” Fortified dairy products (especially milk and margarine) as well as fatty fish and egg yolks are significant dietary sources of vitamin D. You may have heard that vitamin D deficiency is a global epidemic, and that deficiencies are related to an increased risk for several chronic health conditions. These include some cancers, cardiovascular disease, hypertension, diabetes, and osteoporosis. Vitamin D status is measured with a simple blood analysis called the 25-hydroxyvitamin D test. A vitamin D deficiency is defined as a blood level less than 20 ng/mL, while vitamin D insufficiency is defined as a level between 20-29.9 ng/mL. While blood levels of 30 ng/mL or higher are considered normal, the optimal blood level of vitamin D has not yet been established. The current RDA for vitamin D is 600 I.U for individuals between the ages of 1 and 70 years, while individuals greater than 70 years need 800 I.U. daily. To put that into perspective, an 8 ounce glass of milk contains about 100 I.U. of vitamin D.  

Because vitamin D insufficiency and deficiency are so common, the vitamin D status of the American population has been carefully monitored via the National Health and Nutrition Examination Survey (NHANES) since 1988. In this survey, which provides a snapshot of our nation’s health, a random sample of several thousand Americans is selected for comprehensive testing each year. Among the tests that are administered is a measure of blood 25-hydroxyvitamin D levels. Researchers then examine the data according to age, gender, ethnicity, vitamin D supplement users versus non-users, and other factors.

In a recent paper published in the American Journal of Clinical Nutrition, researchers reported on changes in the vitamin D levels of the US population from 1988 through 2010. The results are summarized in Figures 1 and 2 below. In Figure 1, we see that vitamin D levels remained fairly stable in both men and women between 1988 and 2006.  Beyond that point we see a modest increase, particularly in females. 

In Figure 2, we see that vitamin D levels improved steadily among whites across the time period studied. While small improvements were also seen the black population over the latter portion of the time period, vitamin D levels in this group were substantially lower than in whites at all time points. Vitamin D levels in the Mexican-American population remained steady throughout the time period; their levels were also substantially lower than that of whites during all time points.

Over this same time period, the percentage of the entire group reporting that they took a vitamin D supplement increased from 23% in 1988-1994 to 35% in 2009-2010. Additionally, the percentage of the entire group reporting that they took 600 I.U./day or more in supplement form increased from 2% in 1988-1994 to 12% in 2009-2010.

This study adds to the body of literature showing that although some progress has been made, vitamin D levels overall in the U.S. population are low. Deficiencies continue to be widespread in the black population. This is thought to be due to the fact that people with darker skin have a much more difficult time making vitamin D from sunlight. Additionally, lactose intolerance is also more common among blacks than in other groups, so dairy consumption is relatively low in that population. Of note, vitamin D fortified lactose-free dairy products are widely available.

I am often asked about vitamin D supplementation. The first step is to have your 25-hydroxyvitamin D level tested. If the results show that you have a deficiency, then your doctor will likely recommend a vitamin D supplement. The dosage will depend on the severity of the deficiency. Your doc will probably also recommend that you increase your intake of reduced-fat dairy and fatty fish (both of which are heart-healthy) in order to boost your vitamin D level!

Reference

Schleicher, R. L., Sternberg, M. R., Lacher, D. A., Sempos, C. T., Looker, A. C., Durazo-Arvizu, R. A.,...Johnson, C. L. (2016).  The vitamin D status of the US population from 1988 to 2010 using standardized serum concentrations of 25-hydroxyvitamin D shows recent modest increases. Am J Clin Nutr, 104:454-461. ajcn.nutrition.org

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