Nearly one in five U.S. adults are taking a vitamin D supplement, and a growing number are taking excessively high doses linked to an increased risk of fractures, falls, kidney stones and certain cancers, a new study from the University of Minnesota in Minneapolis suggests.
Vitamin D helps the body use calcium to support bone health. The recommended daily intake of vitamin D for most adults is 600 IU (international units), or 800 IU after age 70.
For the study, researchers examined nationally representative survey data collected for 39,243 adults from 1999 to 2014 to see how many people took daily doses of more than 1,000 IU and how many were taking more than 4,000 IU, which is the upper daily amount to avoid dangerous side effects.
The proportion of people taking more than 1,000 IU daily surged from just 0.3 percent in the first survey in 1999-2000 to 18 percent in the last survey in 2013-2014, researchers found. Over that same period, the proportion of adults talking 4,000 IU daily or more climbed from 0.1 percent to 3.2 percent.
Potential dangers of too much vitamin D
Excessive intake of vitamin D can be harmful, as it can cause over-absorption of calcium and cause excess blood calcium which, in turn, can lead to calcium deposits in soft tissues, such as the heart and kidneys.
High doses of vitamin D were most common among women, the elderly and white people.
Previous research links high doses of vitamin D supplements to an increased risk of serious side effects, particularly when it’s used in combination with calcium supplements. Some studies suggest high doses may be associated with an elevated risk of prostate and pancreatic cancers, and deaths from all causes.
The study wasn’t a controlled experiment designed to examine the risks and benefits of varying amounts of vitamin D supplementation.
Vitamin D sources
Some people take vitamin D because it isn’t found in many foods – liver, salmon, sardines, and egg yolks as well as fortified milk and orange juice contain the nutrient. Fortified milk and plant-based beverages contain 100 IU of vitamin D per one cup (250 ml).
Most multivitamins typically contain 400 IU, although some have 800 or 1000 IU.
Supplements are important to consider for people over 50, or who are younger but don’t get much sun, individuals with dark skin and people who live at higher latitudes.
Generally younger or otherwise healthy people with adequate sun exposure are less likely to have low vitamin D levels. However, sunscreen blocks vitamin D production in the skin.
For most people, 1000-2000 IU of vitamin D daily is a very safe level of supplementation which will keep the most people in a sufficient blood range.
More vitamin D is not always better.
Source: JAMA, online June 20, 2017.
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