Millions of people around the world take vitamin D supplements to support their health, especially during winter when sunlight exposure is limited.
Vitamin D is widely known for helping maintain strong bones, healthy muscles, and a well-functioning immune system. But scientists are now discovering that not all vitamin D supplements may work in the same way.
Researchers from the University of Surrey, the John Innes Centre, and Quadram Institute Bioscience have found evidence suggesting that vitamin D2 supplements may lower the body’s levels of vitamin D3, the form considered more effective for human health.
Their findings were published in the scientific journal Nutrition Reviews.
Vitamin D is sometimes called the “sunshine vitamin” because the body naturally produces vitamin D3 when sunlight reaches the skin. However, during winter months, many people do not get enough sunlight to maintain healthy vitamin D levels. This is especially common in northern countries such as the United Kingdom.
To help prevent deficiency, UK health authorities recommend that people consume around 10 micrograms of vitamin D each day during autumn and winter.
There are two major forms of vitamin D found in supplements. Vitamin D2 usually comes from plant or fungal sources, while vitamin D3 is commonly produced from animal-derived ingredients or newer plant-based alternatives.
For years, both forms were considered acceptable ways to improve vitamin D status. However, researchers have increasingly questioned whether vitamin D2 and D3 have identical effects inside the body.
To investigate this issue, scientists carried out a large analysis of previous randomized controlled trials. These studies compared people taking vitamin D2 supplements with people who were not taking them.
The researchers discovered that vitamin D2 supplementation often caused vitamin D3 levels to decrease. In some cases, vitamin D3 levels dropped below those found in people who did not take vitamin D2 supplements at all.
The findings surprised researchers because vitamin D supplements are generally expected to increase overall vitamin D status, not reduce one form of it.
Lead researcher Emily Brown from the University of Surrey explained that while vitamin D supplements remain important, especially during winter, the study suggests vitamin D3 may provide greater overall benefits for many individuals.
Scientists say vitamin D3 appears to be more effective because it is the form naturally produced by the human body. Earlier studies have also suggested that vitamin D3 may stay in the bloodstream longer and raise vitamin D levels more efficiently than vitamin D2.
The research also connects to another important area of health: immune function.
An earlier study published in Frontiers in Immunology, led by Professor Colin Smith from the University of Surrey, found that vitamin D3 may help stimulate an important immune defense system called type I interferon signaling.
This system acts as part of the body’s first line of defense against viruses and bacteria. According to the researchers, vitamin D3 appeared to strengthen this immune response, while vitamin D2 did not show the same effect.
Scientists believe this difference may help explain why vitamin D3 could provide broader health benefits beyond bone support alone.
Vitamin D deficiency continues to be a major global health concern. Low vitamin D levels can contribute to weak bones, osteoporosis, muscle weakness, fatigue, and increased risk of fractures. Researchers are also studying possible links between vitamin D and infections, autoimmune diseases, heart health, and mood disorders.
The findings may be especially important for people following vegetarian or vegan diets. Historically, vitamin D2 has often been used in plant-based supplements because traditional vitamin D3 usually comes from animal sources.
However, researchers now emphasize the importance of making plant-based vitamin D3 products more widely available. Newer vegan-friendly vitamin D3 supplements made from algae or lichen are already becoming more common.
Professor Cathie Martin from the John Innes Centre said the study highlights why plant-based vitamin D3 accessibility is important for public health.
At the same time, experts caution that people should not panic or immediately throw away vitamin D2 supplements. Both forms still help increase vitamin D intake, and individual medical needs can vary.
Researchers also note that more studies are still needed. Scientists want to better understand exactly why vitamin D2 lowers vitamin D3 levels and how these differences affect long-term health outcomes.
Professor Martin Warren from Quadram Institute Bioscience stressed that vitamin D deficiency remains widespread and that identifying the most effective supplementation strategies is essential for improving public health.
The study also highlights how nutrition science continues to evolve. Nutrients that once appeared nearly identical may actually have important biological differences that only become clear through detailed research.
For now, the findings suggest that vitamin D3 may be the preferred choice for many people seeking to support bone health and immune function, although healthcare professionals should still guide individual supplement decisions.
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.
The study was published in Nutrition Reviews.
Source: University of Surrey.
