Vitamin D

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Summary

Vitamin D is really important for your bones, immune system, and mental health. Symptoms of vitamin D deficiency can include fatigue, aches, pain, and depression. Vitamin D supplements help keep your levels steady and can treat deficiencies.

Vitamin D: essential info
Causes
What are my options?
FAQ

Reviewed on September 03, 2025. by

Dr Alexandra Cristina Cowell

Writer & Clinical Content Reviewer

Next review due on September 03, 2028

Last updated on December 04, 2025

Find the vitamin d treatment that’s best for you.

We’ve got a range of options, and our clinicians can help you find the one that’s best for your body and your budget.

Cholecalciferol

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Daily tablets to help supplement your vitamin D levels, or treat deficiency.

Starting at $74.95

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What is vitamin D?

Vitamin D helps to keep the calcium and phosphate in your body in check. Calcium and phosphate play an important role in keeping your bones, muscles, and teeth healthy.

A lack of vitamin D can lead to low bone density, which can lead to brittle bones and deformities. So you’re less likely to experience these complications if you get the right amount.

Often referred to as the sunshine vitamin, you get most of the vitamin D you need from the sun. But this becomes more difficult during winter. Because there’s less sunlight during these months, it’s recommended that you take supplements.

Who needs vitamin D?

Everyone. Vitamin D not only affects your bones, teeth, and muscles, but your mood and your immune system, too. Vitamin D deficiencies have been linked to depression,¹ muscle cramps and, in the most severe cases, osteoporosis,² which is where your bones are so brittle that they break easily or become deformed.

How common is vitamin D deficiency?

It’s estimated that over a billion people worldwide suffer from some form of vitamin D deficiency.³ It can be easily avoided though. Supplements and treatments are usually very affordable, even if you need a high strength treatment.

Treated trusted source:

Penckofer, S, Et al. 2010. Vitamin D and Depression: Where is all the Sunshine? HHS Public Access. USA.
Sunyecz,J. 2008. The use of calcium and vitamin D in the management of osteoporosis. Dove Press. U.S.A.
Naeem, Z. 2010. Vitamin D Deficiency- An Ignored Epidemic. International Journal of Health Sciences. U.S.A.

This page was medically reviewed by Dr Alexandra Cristina Cowell on September 03, 2025. Next review due on September 03, 2028.

How we source info.

When we present you with stats, data, opinion or a consensus, we’ll tell you where this came from. And we’ll only present data as clinically reliable if it’s come from a reputable source, such as a state or government-funded health body, a peer-reviewed medical journal, or a recognised analytics or data body. Read more in our editorial policy.

What causes vitamin D deficiency?

There are a range of factors that can cause vitamin D deficiency, but it’s usually due to a lack of sunlight. Because your body gets most of its vitamin D from the sun, this can become a problem in winter, when it’s darker.

This isn’t to say that the sun is the only source of vitamin D; you also get a small amount from food, as well as fortified food (where vitamin D has been added) such as cereals and margarines.

What are the symptoms of vitamin D deficiency?

It’s not only serious vitamin D deficiencies that can cause health problems. Less severe vitamin D symptoms include depression, general aches and pains, and low energy.

If you notice these symptoms in the middle of winter, or if you spend much of your time indoors, there’s a good chance that you’re suffering from a lack of Vitamin D. Taking a daily supplement is one of the most efficient ways of avoiding or treating these symptoms.

The vitamin D supplement dose is much lower than those given for treatments, but you should still not exceed the recommended daily dose. Daily maintenance doses are the best way to keep your vitamin D levels healthy and stop more serious issues from happening.

Can vitamin D deficiency lead to other problems?

A severe lack of vitamin D can lead to a bone condition called osteoporosis. This is where a lack of calcium leads to brittle bones or other serious deformities.

Severe vitamin D deficiency symptoms can be caught early if you notice muscle cramps, joint pain and general fatigue. These may be early warning signs that a more serious vitamin D deficiency is developing.

Getting significantly more vitamin D into your body over a number of weeks can help, although it won’t completely reverse more extreme deficiencies. All treatments for severe vitamin D deficiencies will need a prescription, as well as careful monitoring by our clinician. Vitamin D deficiency treatment doses usually depend on the severity of your condition.

This page was medically reviewed by Dr Alexandra Cristina Cowell on September 03, 2025. Next review due on September 03, 2028.

How we source info.

What medications are there for vitamin D deficiency?

There are three main reasons why you might want to take vitamin D:

as a supplement to avoid your levels becoming too low;
as a treatment for severe deficiencies; or:
as a maintenance dose, which you’ll likely need after treatment (and should continue taking regularly).

Supplements are the lowest doses of vitamin D. They’re effective for prevention and treating milder deficiencies. They can be bought over the counter from your local pharmacy.

Treatment doses are more varied than supplement doses. They’re generally taken over a specific period of time to tackle severe deficiencies as quickly and safely as possible. After this, it’s likely that you’ll need to keep taking a maintenance dose.

Is there a ‘best’ treatment for vitamin D deficiency?

‘Best’ will depend on what you’re taking it to help with. If you’re just looking to prevent any vitamin D deficiencies from setting in over the winter, it’s likely that a low dose will be sufficient. But you’ll need an increased dose to treat any symptoms of a deficiency.

Vitamin D can come in a range of forms as well, from tablets to capsules to melt-on-the-tongue strips. They may also contain different ingredients, so some vitamin D supplements and treatments are more suitable for vegetarians or vegans than others. There are kosher or halal options available too.

So what’s best for you might not be best for someone else. If you’re unsure which vitamin D treatment is the right one for your needs, speak with our physician. They’ll take your health background into consideration and advise you on your treatment options from there.

Does vitamin D deficiency always need treatment?

Many people can become a bit deficient in vitamin D throughout the winter, and it won’t always lead to more severe deficiencies. But you will be healthier during this period if you’re making sure that you’re getting enough vitamin D to keep your body and mind working properly.

More severe vitamin D deficiencies, though, should be treated. This is because having low levels of vitamin D for long periods of time can easily lead to osteoporosis.

How we source info.

Vitamin D: FAQ

Have something specific you want to know? Search our info below, or ask our experts a question if you can’t find what you’re looking for.

How is vitamin D deficiency diagnosed?

Answer:

You’ll usually be able to diagnose a growing deficiency in vitamin D with your physician by checking for common symptoms, such as fatigue, cramps, and pain in your joints (especially if you’re noticing these issues in the autumn or winter months).

More severe deficiencies might need a blood test to be identified.

Are there different types of vitamin D?

Answer:

Vitamin D2 and vitamin D3 are different forms of vitamin D that come from different sources (vitamin D2 comes from vegetable sources, while vitamin D3 comes from animal sources).

Both vitamin D2 and D3 supplements are available, but vitamin D3 is better processed in the body, as well as more easily stored.

Supplements are synthetic versions of these vitamins. Vitamin D3, for example, comes in a form called colecalciferol, while vitamin D2 supplements are called ergocalciferol. Essentially, both vitamin D forms work in the same way (by regulating calcium levels), but vitamin D3 is generally considered to be a better option than D2. Because of this, it’s the form of vitamin D that you’ll most commonly see in supplements.

Are there tests for vitamin D deficiency?

Answer:

There are blood tests you can take to check if you’re suffering from a vitamin D deficiency, but you’ll only need them if you’re experiencing a severe deficiency. If your symptoms are only mild, you should be able to get low doses of vitamin D from your local pharmacy or supermarket without the need for a prescription or diagnosis.

Some vitamin D supplements and treatments need a prescription, but this is usually only because they’re not suitable for everyone. So our physicians will need to ask you some questions to make sure that they’re safe for you to take.

Can you get side effects from vitamin D supplements?

Answer:

For the most part, it’s very unlikely you’ll experience any problems or side effects with vitamin D. Even the most common issues present in less than 1 in 100 people, and in many of these cases, they occur when you’ve exceeded the recommended dose.

The most common side effects are hypercalciuria (too much calcium in the urine) and hypercalcemia (too much calcium in the blood).

Hypercalcemia is a dangerous condition that requires immediate medical attention. Symptoms are: constipation, loss of appetite, headaches, confusion, depression, excessive thirst, abdominal pain, tiredness, and muscle pain.

Allergic reactions are rare, but it’s important that you know what to look for in case they do happen. Seek immediate medical attention if you notice any of the following: swollen lips, mouth, throat, face, severe itching, hives, or difficulty breathing.

Do vitamin D supplements always work?

Answer:

They are known to be effective for many people when taken correctly. You might not always notice that it’s working, but taking the right amount of vitamin D, especially during winter, will help to keep you healthy until you can get a good amount of vitamin D from sunlight again.

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