American adults are taking vitamin D supplements at a higher rate than suggested, which can lead to negative health consequences.
Vitamin D helps the body use calcium to support bone health, and the recommended daily intake for most adults is 600 IU.
However, a new study found some adults are taking excessively high doses, causing an increased risk of fractures, falls, kidney stones and certain cancers.
There was nearly an 18 percent increase in adults who took a daily dose higher than 1,000 IU and a three percent surge in those who took more than 4,000 IU daily.
These alarmingly high rates have experts concerned that many people aren’t aware of the dangerous side effects these supplements can potentially cause.
There has been a surge of Americans taking extremely high vitamin D doses, which can lead to kidney stones, cancer and fractures
HOW VITAMIN D CAN MAKE BONES WEAK
Experts found some people take far too much vitamin D, which can lead to a range of serious health problems and may even weaken rather than strengthen bones.
Vitamin D is made in the skin by the action of sunlight. In spring and summer, when the sun is sufficiently strong, this is the main source for most people and any excess we make is stored in the fat and liver.
With very high doses of vitamin D there is a danger of hypercalcaemia, the build-up of excessive levels of calcium in the blood, which can cause lethargy, high blood pressure, heart problems, hardening of the arteries and kidney damage.
In 2014 the Food Standard Agency’s Committee on Toxicity concluded: ‘High intakes of vitamin D from medication or dietary supplements (often over prolonged periods) have caused toxicity in humans, and many cases of such poisoning have been reported’.
It said 4,400 IU is the highest amount that could be consumed every day over a lifetime by an adult or child aged 11 to 17 without risk to health (it’s 2,000 IU for children aged one to ten, and 1,000 IU for infants).
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.
Senior study author Pamela Lutsey said: ‘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.’
The public health researcher at the University of Minnesota in Minneapolis added: ‘Excessive intake of vitamin D can, however, be harmful, as it can cause over-absorption of calcium.
‘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.
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MEN WITH GOOD VITAMIN D LEVELS ARE MORE LIKELY TO HAVE HEALTHY KIDS
Men with good levels of vitamin D in their bachelor years are more likely to have healthy children when they start a family.
That is according to a May study by University College Dublin, which found a direct link between a child’s height and weight at five years old, and their father’s pre-conception vitamin levels.
While previous studies have shown maternal vitamin D intake before pregnancy affects a baby’s health, this is one of the first to study the same in men.
Skin exposure to sunlight is essential for the body to produce vitamin D, so the authors also looked at the number of hours children aged five spent playing outdoors during summer.
They found that spending three or more hours playing outdoors during weekends was related to increased height at five years old.
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.
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.