Use of Vitamin D Supplements Skyrocketed in Recent Years

Norra MacReady

June 20, 2017

Daily intake of vitamin D supplements among American adults has increased sharply since 1999, raising questions about the potential risks of high doses, the authors of a new study warn.

According to data from the National Health and Nutrition Examination Survey, the number of American adults taking at least 1000 international units (IU) vitamin D has increased from 0.3% in 1999-2000 to 18.2% in 2013-2014.

What is more, by 2014, "3% of the population exceeded the tolerable upper limit of 4000 IU daily, and may be at risk of adverse effects as a consequence," Mary R. Rooney, MPH, and colleagues write in an article published online today in JAMA.

The recommended dietary allowance for vitamin D is 600 IU per day for adults up to 70 years of age and 800 IU per day thereafter. Consumption of 1000 IU per day or more is considered evidence of supplementation.

In 2011, the Institute of Medicine (now the National Academy of Medicine) issued a report concluding that although vitamin D was good for bone health, evidence of other benefits are inconclusive, and daily doses above 4000 IU might have adverse effects such as hypercalcemia.

For a clearer picture of recent trends in vitamin D supplementation, Rooney, from the Division of Epidemiology and Community Health at the University of Minnesota, Minneapolis, and colleagues analyzed National Health and Nutrition Examination Survey data from 1999 to 2014. The survey provides a nationally representative snapshot of nutritional data from a diverse sample of noninstitutionalized US citizens.

The authors used data from 39,243 participants 20 years of age or older who had reported their use of vitamin D supplements for the last 30 days and presented their supplement bottles to confirm their claims. They had a mean age of 46.6 years (standard deviation [SD], 16.8 years), 51.1% were women, and 69.7% identified as non-Hispanic white.

The overall prevalence of daily intake of at least 1000 IU vitamin D was 0.3% (95% confidence interval [CI], 0.1% - 0.5%) in the 1999-2000 survey and rose steadily in each subsequent period to 18.2% (95% CI, 16.0% - 20.7%) in 2013-2014. Moreover, daily intake of 4000 IU or more went from a prevalence of 0.2% (95% CI, 0.1% - 0.4%) in 2007-2008 to 3.2% (95% CI, 2.5% - 4.0%) in 2013-2014 (P for trend < .001 in both comparisons).

Significant upward trends were noted for most of the age and ethnic groups studied, and for both sexes (P for trend < .001 in all applicable comparisons). However, consumption of doses at or above the tolerable upper limit was most frequent among women (4.2%; 95% CI, 3.0% - 5.7%), non-Hispanic whites (3.9%; 95% CI, 3.0% - 5.1%), and people at least 70 years of age (6.6%; 95% CI, 4.2% - 10.2%).

There is evidence that high doses of vitamin D may increase the risk for falls and fractures, the authors write. Other studies have shown an association between high blood levels of 25-hdyroxyvitamin D with prostate cancer, pancreatic cancer, and all-cause mortality, and vitamin D taken with calcium may increase the risk for kidney stones.

Study limitations include a lack of information on clinical outcomes and reliance on self-reported intake of vitamin D, although this was supported by showing the supplement bottles. Also, the survey design is serial and cross-sectional, rather than longitudinal.

"Characterizing trends in vitamin D supplementation, particularly at doses above the tolerable upper limit, has important and complex public health and clinical implications," the authors conclude.

One author reports receiving personal fees from Siemens Healthcare Diagnostics. No other relevant financial conflicts of interest were disclosed.

JAMA. 2017;317:2448-2450. Abstract

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