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Vitamin D is known to be essential to many aspects of human health — but a new study suggests that taking a certain form of it can have a negative effect.

The more potent and longer-lasting form, vitamin D3 (cholecalciferol) is produced naturally when the body is exposed to sunlight and is also found in animal products, while vitamin D2 (ergocalciferol) comes from plant or fungal sources, per the National Institutes of Health.

Researchers from the University of Surrey in the U.K. found that taking vitamin D2 can cause reduced levels of vitamin D3 in the body.

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They made this determination by analyzing 11 randomized controlled trials including 655 adults, which showed that people taking vitamin D2 supplements had less vitamin D3 than those who did not take D2, according to a university press release.

The findings of the study — conducted along with the John Innes Centre and the Quadram Institute Bioscience in Norwich, England — were published in the journal Nutrition Reviews.

“Vitamin D supplements are important, especially between October and March, when our bodies cannot make vitamin D from sunlight in the U.K.,” lead researcher Emily Brown, a Ph.D. research fellow from the University of Surrey’s Nutrition, Exercise, Chronobiology & Sleep Discipline, stated in the press release.

“However, we discovered that vitamin D2 supplements can actually decrease levels of vitamin D3 in the body, which is a previously unknown effect of taking these supplements. This study suggests that, subject to personal considerations, vitamin D3 supplements may be more beneficial for most individuals over vitamin D2.”

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Previous research has suggested that the two forms of vitamin D are not interchangeable. A study published in Frontiers in Immunology, also conducted by the University of Surrey, found that vitamin D3 is more effective in boosting the immune system and protecting the body from viral and bacterial diseases, the release noted.

Some foods containing vitamin D3 include fatty fish, egg yolks, cod liver oil and fortified dairy and animal foods, health sources confirm.  (iStock)

“We have shown that vitamin D3, but not vitamin D2, appears to stimulate the type I interferon signaling system in the body – a key part of the immune system that provides a first line of defense against bacteria and viruses,” stated Professor Colin Smith, who led the above study. “Thus, a healthy vitamin D3 status may help prevent viruses and bacteria from gaining a foothold in the body.”

Professor Martin Warren, chief scientific officer at the Quadram Institute, confirmed in the release that vitamin D deficiency is a “significant public health concern,” particularly during the winter months. 

“This collaborative research effort aligns well with the Quadram Institute’s mission to deliver healthier lives through food innovation to enhance the nutrient density of the food we eat,” he said. “Tackling this with the most effective form of vitamin D supplementation or fortification is of the utmost importance to the health of the nation.”

More research is needed to determine whether vitamins D2 and D3 affect the body differently — and whether that could change doctors’ medical advice on which type to take, the researchers concluded. (iStock)

More research is needed to determine whether vitamins D2 and D3 affect the body differently — and whether that could change doctors’ medical advice on which type to take, the researchers concluded.

There were several limitations to the analysis, the study findings noted.

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For example, there were only a small number of studies with many differences among them, such as their duration, the amount and timing of doses, and how results were measured. There was also the potential for biases due to incomplete reporting of details.

The results could also be affected by factors such as the amount of sunlight exposure, as well as some people taking supplements and others eating vitamin-fortified foods, the researchers noted.

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Some foods containing vitamin D3 include fatty fish, egg yolks, cod liver oil and fortified dairy and animal foods, health sources confirm. Vitamin D2 can be found in mushrooms, fortified foods and some plant/fungal-based supplements.

The study was supported by the Biotechnology and Biological Sciences Research Council (BBSRC).