Millions of people around the world take vitamin D supplements to support their health.
Many hope these supplements will strengthen their bones, improve their immune system, and help protect them during the darker winter months when sunlight is limited.
But new research suggests that not all vitamin D supplements work in the same way, and one type may even reduce levels of the form of vitamin D that the body uses most effectively.
The study was carried out by researchers from the University of Surrey, the John Innes Center, and the Quadram Institute Bioscience.
Scientists closely examined two common forms of vitamin D found in supplements: vitamin D2 and vitamin D3. Both are sold widely in pharmacies and health stores, and both can raise total vitamin D levels in the body. However, the researchers discovered an important difference between them.
They found that when people took vitamin D2 supplements, their blood levels of vitamin D3 often dropped. This was surprising because vitamin D3 is the form naturally produced by the body when the skin is exposed to sunlight. It is also considered by many experts to be the more effective form for improving overall vitamin D status.
In several studies reviewed by the researchers, people taking vitamin D2 ended up with lower vitamin D3 levels than people who were not taking any supplement at all. This finding raised concerns that vitamin D2 may not support the body in the same way as vitamin D3.
The research was published in the journal Nutrition Reviews. According to Dr. Emily Brown from the University of Surrey, vitamin D supplements are especially important during the colder months of the year.
Between October and March in the United Kingdom, sunlight is often too weak for the body to make enough vitamin D naturally through the skin.
Vitamin D plays a major role in keeping bones and muscles healthy because it helps the body absorb calcium. Low vitamin D levels can increase the risk of weak bones, fractures, muscle pain, and tiredness.
Scientists have also been studying vitamin D because of its possible effects on the immune system, mental health, heart health, and other areas of the body.
Although many people know vitamin D as the “sunshine vitamin,” modern lifestyles make deficiency increasingly common. People spend more time indoors, wear sunscreen, or live in places with long winters and less sunlight.
Older adults, people with darker skin, and those who cover most of their skin outdoors may also struggle to produce enough vitamin D naturally.
Because of this, supplements are widely recommended in many countries. However, the new study suggests that choosing the right type of vitamin D supplement may matter more than people realize.
Researchers explained that vitamin D2 and vitamin D3 may behave differently inside the body. Vitamin D2 usually comes from plant or fungal sources, while vitamin D3 is often produced from animal sources or made in the skin through sunlight exposure.
In recent years, plant-based vitamin D3 options have also become more available for vegetarians and vegans.
Earlier research from the University of Surrey had already suggested that vitamin D3 may provide extra benefits beyond simply raising vitamin D levels.
In a previous study published in Frontiers in Immunology, Professor Colin Smith and his team found that vitamin D3 appeared to activate a part of the immune system known as the type I interferon signaling system. This system helps the body defend itself against bacteria and viruses.
The researchers did not find the same effect with vitamin D2. This suggested that vitamin D3 may play a stronger role in helping the immune system respond to infections. Maintaining healthy vitamin D3 levels, scientists said, could help reduce the risk of illnesses taking hold in the body.
The new findings are important because vitamin D deficiency is already a major public health concern in many countries. Experts believe that choosing the most effective form of supplementation or food fortification could help improve the health of large populations, especially during winter.
Professor Martin Warren from the Quadram Institute explained that understanding these differences could help guide future health recommendations.
Professor Cathie Martin from the John Innes Center added that increasing the availability of plant-based vitamin D3 products would help ensure that more people could benefit from the more effective form of supplementation.
The scientists also stressed that more research is still needed. Although current evidence points toward vitamin D3 being the better choice for most people, researchers want to continue studying how both forms affect the body over longer periods of time.
For now, the findings suggest that vitamin D3 may be the preferred option for maintaining healthy vitamin D levels and supporting the immune system.
As scientists continue to learn more about how these vitamins work inside the body, the research may help doctors and health experts give clearer advice about the best ways to prevent vitamin D deficiency and support long-term health.
If you care about nutrition, please read studies about the power of beetroot juice, and the risks of mixing medications with dietary supplements.
For more health information, please see recent studies about how to boost iron intake: natural solutions for anemia, and results showing vitamin K may lower your heart disease risk by a third.
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