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Health organizations such as the UK’s national health services recommend that adults take 10 micrograms, or 400 international units (IU) of vitamin D every day, while the National Institutes of Health advise that most adults take 600 IU, with both bodies cautioning against taking more than 4,000 IU per day. Having too much vitamin D can cause a build-up of calcium (钙) in the blood, leading to symptoms such as nausea and kidney stones.

But Patrick J. LaRiccia at the University of Pennsylvania and his colleagues recently found that a daily dose (一剂) of 5,000 IU may reduce the risk of influenza-like symptoms. They wondered whether this higher-than-recommended dosage may also have other positive effects.

So the team asked 196 adults to take 5,000 IU of vitamin D3 every day for about nine months. The adults, aged 47 on average, were aware of the dose they were having. The researchers also analyzed the data of more than 1,900 people who weren’t given the 5,000 IU daily dose of vitamin D. However, they were free to take vitamin D supplements if they wished. Towards the end of the study, across this group, the average reported dose was 1,318 IU and the average age was 50.

Over 10 months, those on the 5,000 IU dose had a lower risk of being hospitalized due to any cause, and they had to visit the emergency room or be admitted to intensive care less than people in the other group. No participants reported side effects.

However, LaRiccia says the team can’t rule out the age difference as a possible cause of these results, with those in the high-dose group potentially avoiding hospital because they were on average three years younger. The nationalities of people in the two groups also differed, with fewer Hispanic and Latino people in the high-dose group, which may have affected the results.

“The findings are promising, but the study was relatively small and the study period was too short to monitor any long-term safety issues of such a high daily dose of vitamin D,” says JoAnn Manson at Harvard University.