Is Vitamin D3 the Same as Vitamin D? Differences, Benefits & Dosage

If you've ever shopped for supplements, you've probably noticed that some products are labelled vitamin D, while others specifically say vitamin D3. It's a common source of confusion, especially during the autumn and winter months when vitamin D supplementation is widely recommended across the UK.

So, is vitamin D3 the same as vitamin D?

The short answer is no. While vitamin D and vitamin D3 are often thought to be the same, vitamin D is actually a broader category that includes two primary forms: vitamin D2 (ergocalciferol) and vitamin D3 (cholecalciferol). 

Although both vitamin D2 and vitamin D3 can help increase vitamin D levels, research suggests that vitamin D3 is generally more effective at raising and maintaining blood vitamin D levels. 

In this guide, we'll explain the differences between vitamin D and vitamin D3, answer common questions about dosage and side effects, and help you decide which form may be right for you. 

What Is Vitamin D?

Vitamin D is a fat-soluble vitamin that helps regulate calcium and phosphate levels in the body. These nutrients are essential for maintaining healthy:

• Bones
• Teeth
• Muscles

Unlike most vitamins, vitamin D also functions as a prohormone, meaning it is converted into an active hormone that performs important functions throughout the body.

Your body can make vitamin D when your skin is exposed to sunlight. However, because sunlight levels in the UK are often insufficient between October and March, many people rely on supplements to maintain adequate vitamin D levels. 

What Is Vitamin D3?

Vitamin D3, also known as cholecalciferol, is the form of vitamin D naturally produced in human skin when exposed to UVB rays from sunlight.

Vitamin D3 is also found naturally in foods such as:

• Oily fish (salmon, mackerel, sardines)
• Egg yolks
• Liver
• Some fortified foods

Traditionally, most vitamin D3 supplements have been derived from lanolin, a substance obtained from sheep's wool. However, vegan vitamin D3 supplements derived from lichen are now widely available.

Vitamin D2 vs Vitamin D3: What's the Difference?

The two main forms of vitamin D used in supplements are vitamin D2 and vitamin D3.

Both forms follow similar pathways in the body.

After being absorbed, they are converted in the liver into 25-hydroxyvitamin D [25(OH)D], the form measured in blood tests. The kidneys then convert this into the active hormone that helps regulate calcium balance and other bodily functions. 

Vitamin D vs Vitamin D3 at a Glance

What Are the Benefits of Vitamin D3?

Vitamin D3 plays several important roles in maintaining overall health.

Vitamin D helps:

• Maintain healthy bones and teeth
• Support normal muscle function
• Help the body absorb calcium and phosphate
• Contribute to normal immune system function

Because vitamin D3 is generally more effective at raising and maintaining vitamin D levels, it is the form most commonly used in UK supplements.

Which Form of Vitamin D Should You Take?

For most people, vitamin D3 is the preferred choice.

Research suggests it may provide better long-term maintenance of vitamin D levels compared to vitamin D2.

Vitamin D supplements are available in several forms, including:

• Tablets
• Capsules
• Oral sprays
• Liquid drops

All forms can be effective when taken correctly.

Because vitamin D is fat-soluble, taking it with a meal containing some fat may help improve absorption.

Should I Take Vitamin D or D3 Daily?

This is one of the most common questions people ask.

The NHS recommends that adults and children over the age of four consider taking a daily supplement containing 10 micrograms (400 IU) of vitamin D during autumn and winter.

Certain groups may benefit from taking vitamin D supplements throughout the year.

The Department of Health and Social Care recommends that adults and children over the age of four consider taking a daily supplement containing 10 micrograms (400 IU) of vitamin D throughout the year if they:

• Spend very little time outdoors, such as those who are frail or housebound
• Live in institutions such as care homes
• Usually wear clothing that covers most of their skin when outside

People with darker skin tones, including those of African, African-Caribbean, or South Asian heritage, may also find it more difficult to produce enough vitamin D from sunlight and should consider taking a daily 10 microgram supplement year-round.. 

NHS Guidance on Vitamin D Supplementation

According to NHS and UK Health Security Agency (UKHSA) guidance, everyone should consider taking a daily vitamin D supplement during autumn and winter.

Additional guidance includes:

• Breastfed babies from birth to one year should receive 8.5–10 micrograms daily.
• Children aged 1–4 years should receive 10 micrograms daily.
• Certain high-risk groups should consider year-round supplementation.

Vitamin D deficiency is generally defined as a blood level below 25 nmol/L, while levels between 25–50 nmol/L are often considered insufficient.

Common Signs of Vitamin D Deficiency

Vitamin D deficiency is relatively common in the UK, particularly during the autumn and winter months.

Possible symptoms may include:

• Fatigue
• Muscle weakness
• Bone pain
• Frequent illness or infections
• Low mood

These symptoms can have many causes and do not necessarily mean you have a vitamin D deficiency.

If you're concerned about your vitamin D levels, speak with your GP or healthcare professional.

Can I Take 10,000 IU of Vitamin D3 Every Day?

For most adults, 10,000 IU daily is significantly higher than routine NHS recommendations.

The NHS advises that adults should generally avoid taking more than 100 micrograms (4,000 IU) per day unless specifically advised by a healthcare professional.

Taking high doses of vitamin D for extended periods can increase the risk of:

• Hypercalcaemia (high calcium levels)
• Kidney problems
• Nausea
• Vomiting
• Weakness
• Excessive thirst

Higher doses may occasionally be prescribed to treat confirmed vitamin D deficiency, but these should only be used under medical supervision.

Does Vitamin D3 Cause Constipation?

Constipation is not one of the most common side effects of vitamin D3 supplementation at standard daily doses.

However, excessive vitamin D intake can sometimes lead to elevated calcium levels in the blood (hypercalcaemia), which may cause:

• Constipation
• Nausea
• Vomiting
• Frequent urination
• Increased thirst
• Weakness

These effects are generally associated with excessive supplementation rather than recommended daily doses.

If you experience persistent constipation or other concerning symptoms while taking vitamin D supplements, speak with your GP or pharmacist.

When Should You Speak to a Healthcare Professional?

You should seek medical advice before taking vitamin D supplements if you have:

• Kidney disease
• Sarcoidosis
• Hypercalcaemia
• Primary hyperparathyroidism
• A history of kidney stones

You should also discuss supplementation with a healthcare professional if you take medications such as:

• Digoxin
• Thiazide diuretics
• Orlistat
• Rifampicin
• Phenytoin
• Long-term corticosteroids

Final Thoughts

Vitamin D and vitamin D3 are not exactly the same thing.

Vitamin D is a broad term that includes both vitamin D2 and vitamin D3, while vitamin D3 refers specifically to cholecalciferol. Although both forms can increase vitamin D levels, research suggests that vitamin D3 is generally more effective at raising and maintaining blood vitamin D levels over time.

For most people in the UK, vitamin D3 is the preferred form of supplementation, particularly during autumn and winter when sunlight exposure is limited.

If you're choosing between vitamin D2 and vitamin D3, vitamin D3 is generally the preferred option due to its effectiveness at maintaining healthy vitamin D levels. However, the best supplement for you depends on your individual health needs, diet, and lifestyle.

Disclaimer

This article is for general informational purposes only and does not constitute medical advice. Always consult a qualified healthcare professional before starting, stopping, or changing any supplement regimen.