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 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 maximum recommended 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 report in JAMA. Over that
same period, the proportion of adults talking 4,000 IU daily or more
climbed from 0.1 percent to 3.2 percent.
“Vitamin D is essential for bone metabolism, as it helps the body
absorb calcium and maintain appropriate concentrations of calcium
and phosphate in the blood,” said senior study author Pamela Lutsey,
a public health researcher at the University of Minnesota in
Minneapolis.
“Excessive intake of vitamin D can, however, be harmful, as it can
cause overabsorption of calcium,” Lutsey said by email. “Excess
blood calcium can, in turn, lead to detrimental deposition of
calcium in soft tissues, such as the heart and kidneys.”
High doses of vitamin D were most common among women, the elderly
and white people, the study found.
In 2013 and 2014, 6.6 percent of people age 70 and older were taking
at least 4,000 IU of vitamin D daily, while none were in 2007. About
6.6 percent of people aged 60 to 69 were also taking this much
vitamin D by the end of the study, as were 4.2 percent of all women
and 3.9 percent of all white participants.
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, the authors note. 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, however, a controlled experiment designed to
examine the risks and benefits of varying amounts of vitamin D
supplementation.
Another limitation of the study is that participants had to
accurately recall and report on their use of vitamin D supplements,
the authors note. People were asked to bring in their pill bottles
to aid in accurate reporting.
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Some people take vitamin D because it isn’t in many foods, though it
can be found in beef liver, canned salmon or sardines, cheese and
egg yolks as well as fortified milk and orange juice. Most milk sold
in the U.S., for example, contains 100 IU of vitamin D per cup.
Daily multivitamins typically contain only about 400 IU, and people
consuming more than this are usually intentionally trying to boost
this specific vitamin, the researchers point out.
Supplements are particularly important to consider for people over
50, or who are younger but don’t get much sun, individuals with dark
pigmentation and people who live at higher latitudes, said Dr.
Matthew Drake, a researcher at the Mayo Clinic in Rochester,
Minnesota, who wasn’t involved in the study.
“Generally younger or otherwise healthy people with adequate sun
exposure are less likely to have low vitamin D levels,” Drake said
by email. However, sunscreen blocks vitamin D production in the
skin, he added.
“For most people, 1000-2000 IU of vitamin D daily is a very safe
level of supplementation which will keep the vast majority of people
in an optimal range,” Drake said.
The study suggests that many Americans are taking more vitamin D
than they should, noted Dr. Karen Hansen, a researcher at the
University of Wisconsin School of Medicine and Public Health in
Madison who wasn’t involved in the research.
“Too much is not always better,” Hansen said by email.
SOURCE: http://bit.ly/2rQUz8C JAMA, online June 20, 2017.
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