New research changes what we know about vitamin D supplements

We’ve long known that having enough vitamin D is important for health: it supports strong bones and is associated with a decreased risk of cardiovascular disease, depression, and diabetes. 

And with 1 in 6 people in the UK having vitamin D deficiency, knowing how to replenish levels properly is crucial, particularly in autumn and winter months. 

This article breaks down the recent study’s findings and what they mean for you.

Are vitamins D2 and D3 at odds?

A recent meta-analysis published in Nutrition Reviews looked at 11 randomised controlled trials involving 655 participants. Researchers found that people taking D2 supplements had a significant drop in their D3, the more effective form of vitamin D. 

Interestingly, it seems that the body has a regulatory feedback loop that ramps up the disposal of D3 when D2 enters the system. The less effective D2 is crowding out D3, which could counterintuitively lower the body’s vitamin D levels over time. 

Researchers suggested that the disposal mechanism involves CYP24A1, an enzyme responsible for regulating the amount of vitamin D in the blood. When total vitamin D rises from D2 supplementation, this enzyme ramps up activity, potentially clearing out D3 along with the excess D2.

The reduction of vitamin D3 was often an incidental finding in studies designed to investigate other outcomes. One study published in 2019 and another from 2012 noted dropping D3 levels in their D2 supplementation groups, but researchers haven’t specifically looked at it until recently.

The same vitamin, but with key differences

Both forms of vitamin D are well-absorbed by the body, but they’re chemically different. Vitamin D2, also called ergocalciferol, is plant-based and found in fortified foods and UV-exposed mushrooms. Vitamin D3 is the form that’s produced when your skin is exposed to sunlight, and it’s mainly found in animal foods like egg yolks and oily fish. 

Research has shown that vitamin D3 causes larger increases in the amount of vitamin D in the blood, which is often referred to as serum 25(OH)D. This is the most reliable biomarker of vitamin D status, and if you have a blood test to check your levels, it’ll likely be this one. 

While both forms of vitamin D are available in supplement form, D3 is the most widely recommended. But with D2 commonly used in vegan-friendly supplements, it’s worth knowing that not all formulations are the same.

How to choose the right vitamin D supplement

For most people, this study confirms existing evidence that D3 is the preferred choice when choosing supplements. 

The challenge lies with vegans and vegetarians, as D3 is typically derived from animal sources. Most commercially available vitamin D3 supplements are made with lanolin, a substance found in sheep’s wool.

Lichen-based vitamin D3, derived from algae, is becoming more widely available. While it boasts a slightly higher price tag than standard vitamin D pills, the premium may be worthwhile for plant-based eaters.

If you live in the UK, don’t be tempted to skip vitamin D supplements in favour of sun exposure. The country’s latitude means that in autumn and winter months, the prevailing sun rays are too weak to enable vitamin D synthesis. 

The NHS recommends supplementing with 10 micrograms (mcg) per day in the autumn and winter. For people who are housebound or spend most of their time indoors, year-round supplementation might be needed. It’s particularly important for people with black and Asian backgrounds, as they don't synthesise as much vitamin D from the sun and have higher rates of deficiency.

Takeaway

If you live in the UK, choose vitamin D3 (cholecalciferol) over D2 (ergocalciferol) in autumn and winter months, as D2 supplementation can deplete your D3 stores. Plant-based eaters can take lichen-derived vegan D3 over standard vegan D2 supplements. 

Disclaimer: This information is for general educational purposes only and isn’t a substitute for professional medical advice, diagnosis, or treatment. Always speak with a qualified healthcare professional if you have questions about your health or before making changes to your care, diet, or routine. If you’re having a medical emergency, please seek help by contacting your local emergency services.