Last updated: 17/10/2022

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If you are concerned about the health of your bones, you have probably heard about Vitamin D. This substance is capable of increasing your calcium absorption and the mineralisation of bone tissue, preventing secondary fractures associated with osteoporosis. Vitamin D3 is one of the most potent forms of Vitamin D.

This vitamin, referred to by some as the “sunshine vitamin,” is much more than just a simple bone booster. This vitamin protects the heart and the brain, helping us to live a life full of energy and free from illness. Would you like to know more about this amazing form of Vitamin D? Keep on reading!


  • There are two types of Vitamin D (D2 and D3) which are derived from different sources (either vegetable or animal). Vitamin D3, or colecalciferol, is the most potent form of Vitamin D.
  • Up to 80% of people have some type of Vitamin D3 deficiency. The most common cause of this deficiency is a lack of exposure to natural sunlight.
  • Be careful–excessive use of Vitamin D3 supplements can cause a buildup of calcium in the arteries.

The Best Vitamin D3 in the United Kingdom: Our Choices

This ranking lists the best Vitamin D3 supplements available right now on We have evaluated the ingredients, the dose and the formula of each product. At the same time we have taken into consideration the reviews of consumers of these products to give you this list of the best available Vitamin D3 supplements:

Shopping Guide: Everything You Need to Know About Vitamin D3 Supplements

Vitamin D is a supplement that functions somewhat like a hormone in the human body. It facilitates the proper functioning of the skeletal, cardiovascular and nervous systems to function at their optimum levels. One of the most potent and effective forms of Vitamin D is Vitamin D3, also known as colecalciferol.

A Vitamin D3 supplement can improve your physical and mental well-being.
(Source: Guillem: 89108330/

What is Vitamin D3?

A vitamin is a substance which is indispensable for life of organisms. Vitamins cannot be created by organisms themselves, and instead must be made from other compounds. Following this definition, it is not totally correct to refer to colecalciferol using the term “vitamin.” This is because the body actually IS capable of producing Vitamin D, when a person’s skin is exposed to direct sunlight.

Vitamin D3 is a liposoluble substance, and is stored in the fatty tissue of the body. Its structure is very similar to that of a cholesterol molecule. In fact, the UV radiation of the sun modifies the structure of cutaneous dehydrocholesterol, synthesising colecalciferol or D3.

Dr. Michael F. HolickVitamin D Expert
“If you think of it as evolutionary, it’s the oldest hormone on this Earth. I don’t think that this is going to be a flash in the pan.”

It is also possible to find Vitamin D3 in animal-based foods we consume, especially fish, eggs and fortified dairy products. Dietary intake of Vitamin D3 is essential for maintaining stable levels of Vitamin D in people who are not exposed to a sufficient amount of direct sunlight.

Why is Vitamin D3 considered the most potent form of Vitamin D?

There are five different types of Vitamin D in existence. Only two forms of this vitamin are relevant to us in the field of human nutrition, they are known as Vitamin D2 (ergocalciferol) and Vitamin D3 (colecalciferol). Both molecules follow the same method of activation in the body and create an active form of Vitamin D.

For a long time it was believed that the only difference between these two vitamins was their origin. Vitamin D2 is found in plant-based foods, while D3 comes from animal-based products. Recent studies have confirmed that colecalciferol is more potent than ergocalciferol, providing a larger quantity of active Vitamin D to the body.

Vitamin D2 Vitamin D3
Origin Mushrooms, lichen and plants

Fortified foods (mainly dairy products and cereal)

Synthesis by the body through exposure to sunlight

Animal-based foods

Some genetically modified mushrooms and lichen

Conversion to active Vitamin D Capable of moderately elevating the concentration of active Vitamin D As an oral supplement, doubles the concentration of active Vitamin D compared to other forms
Existence of vegan supplements Yes Uniquely formed from a base of mushrooms or lichen
Absorption High, if the absorption of fat is adequate High, if the absorption of fat is adequate
Toxicity In high quantities In high quantities

In the above table, you can see how Vitamin D3 and D2 are very similar substances which are equally absorbent and are both potentially toxic (if they are taken incorrectly). However, the difference between the two molecules lies in their effectiveness, with D3 being the preferred supplement of experts in the field. However, it needs to be taken with caution as it D3 can cause serious health problems if taken in excess.

How does my body absorb Vitamin D3?

The human body absorbs Vitamin D3 either through exposure to direct sunlight or the ingestion of foods rich in Vitamin D3, whereby the molecule colecalciferol passes into the bloodstream. This substance is then metabolised by the liver and the kidneys to produce, after many different reactions, the active form of Vitamin D known as calcitriol. Therefore, any illness affecting the liver or renal systems can affect the levels of active Vitamin D in the body and how efficiently they are being processed. In this case, taking a vitamin D3 supplement can cause a buildup of this substance which cannot be converted into its active form, and will instead become toxic.

Fortified milk is high in Vitamin D3.
(Source: Kuzmina: 36587787/

All experts agree that the safest and most effective way of obtaining an optimal level of vitamin D3 is from exposure of the skin to direct sunlight. However, people who spend the majority of their time indoors, have sensititvity to the sun or live in a place with very little sunlight at certain times of the year can obtain this substance from their diet, as long as they follow their doctor’s advice.

What is the function of Vitamin D3?

Vitamin D3 performs as an inactive hormonal precursor, which means, it is a substance that needs to be transformed (hydroxylated) before passing into its active form. Calcitriol, or active Vitamin D, works as a hormone capable of regulating a wide range of functions in the human body. Some of these functions are shown in the following table:

System Function
Bone Increase of the absorption of calcium on an intestinal level, repairs damaged bones and creates new bone tissue
Muscular Muscular contraction (including cardiac musculature)
Cardiovascular Control of arterial dilatation, control of arterial pressure and control of cardiac functionality
Pulmonary Control of inflammatory mechanisms
Renal Adjusts renal function and controls the levels of phosphorus and calcium
Reproductive Synthesis and regulation of sexual hormones
Immune Strengthens the defensive system, regulates autoimmunity and controls excessive cellular growth (tumours)
Nervous Neural protection and mood control
Hormonal Control of hormonal production (especially insulin) and controls weight and appetite

Most Vitamin D3 will be activated int he body with the eventual purpose of controlling the absorption of calcium and the amount deposited in body tissue. The remaining colecalciferol will be transformed into calcitriol, becoming a molecule essential to different organic processes, such as those that regulate appetite and mood.

What is the recommended daily intake of Vitamin D3?

The recommended daily intake (RDI) of Vitamin D3 depends on various individual factors, such as age, gender and the particular circumstances of each individual. Although the best source for an exact dose and dosage is your personal physician, the scientific community has been able to reach a general consensus about the RDI of colecalciferol, which you can see in the following table:

Population group RDI Vitamin D3
Babies 0-6 months 400 IU or 10 μg
Babies 6-12 months 400 IU or 10 μg
Children 1-3 years 600 IU or 15 μg
Children 4-8 years 600 IU or 15 μg
Adolescents 9-18 years 600 IU or 15 μg
Adults up to 70 years 600 IU or 15 μg
Women over 70 years 800 IU or 20 μg
Men over 70 years 800 IU or 20 μg

Determining an appropriate unit of measure for vitamin D3 is more complicated than for other nutrients, because its true level of functionality will be dictated by the quantity of calcitriol or active Vitamin D which is generated by colecalciferol. Experts advise that this molecule should measured in International Units (IU).

The IU of Vitamin D3 gives information about the quantity of colecalciferol which will be transformed into a biologically active form. It is also possible to measure the RDI of this molecule in micrograms (μg) or in nanograms (ng). On the internet you can find various calculators capable of converting these units.

What problems can come from a Vitamin D3 deficiency?

A Vitamin D3 deficiency can initially cause nonspecific symptoms, mainly fatigue and weariness which are often difficult to describe. Later, painful sensations can present in different areas such as around the spinal cord, pelvis and legs. Some symptoms can be confused with other types of rheumatic illnesses or with injuries caused by excessive exercise.

These issues are caused by a deficit of the mineralisation of bones, which increases the incidence of fractures (especially of the hip), muscle and ligament injuries. Osteoporosis can occur in older people, while in younger people a defect in the growth of bones called rickets can appear.

A deficiency in colecalciferol can also affect the regulation the growth of cells. This could increase the frequency of the occurence of some types of tumours and autoimmune diseases such as psoriasis. The immune system will also suffer a diminished ability to ward off infections.

The metabolism of our bodies body can also be affected by a Vitamin D3 deficiency, diminishing the response to insulin, while elevating the level of blood sugar and causing difficulty in controlling weight. Blood pressure regulation will also be affected, increasing the incidence of high blood pressure.

What are the causes of a Vitamin D3 deficiency?

It is possible to separate the causes of a colecalciferol deficiency into three large groups: a diminished capacity to synthesise of Vitamin D3, an insufficient ingestion of colecalciferol, and the malabsorption of this Vitamin. In the following paragraphs you will find detailed information about these three causes of hypovitaminosis.

Tablets or capsules are the most common form of Vitamin D3 supplements.
(Source: Gigowaska: 88930098/

Diminished Capacity to Synthesise Vitamin D3

  • Lack of exposure to sunlight: People in the hospital, a nursing home or a rehabilitation facility; those working at night and sleeping during the day; and sedentary people all have less exposure to sunlight, which will diminish the production of Vitamin D3 in such people.
  • Lack of solar radiation: People who dress modestly, with most of their body covered up, can be limit exposure of their skin to solar rays to the point of causing an increase in their risk of a developing Vitamin D3 deficiency. Sunscreen and, somewhat surprisingly, environmental pollution are capable of blocking the sun’s Vitamin D3-producing rays.
  • Geographic location and time of the year: Solar radiation is weaker and is of shorter duration in the colder months of the year. This diminishes the quantity of vitamin D3 that can be created from exposure to sunlight. This effect is even more pronounced in the northernmost areas of Northern Europe and North America.
  • Heavily pigmented skin: Melanin is the pigment that gives skin its colour. People with dark skin have a larger amount of melanin in their epidermis, which protects them from sunburn but also diminishes the ability to synthesise Vitamin D3 through the skin.
  • Advanced age: The natural capacity of the skin to produce Vitamin D3 from exposure to sunlight declines with age. People over the age of 70 have a higher risk of suffering hypovitaminosis, even if they stay active and are exposed to substantial sunlight.

Oysters contain a large concentration of Vitamin D3.
(Source: Grecaud: 57557070/

Insufficient Ingestion of Vitamin D3

  • Vegans and vegetarians: Colecalciferol is a molecule which is very difficult to include in a diet that lacks any animal-based products. Vegans will ingest less Vitamin D3 and will have a higher risk of developing hypovitaminosis, if such persons do not get enough exposure to sunlight.
  • Inadequate diet: A diet which is heavy in processed foods (sweets, fast food and frozen meals) and low in foods rich in Vitamin D3, such as fish or dairy products, will increase the risk of suffering some type of deficiency.

Malabsorption of Vitamin D3

  • Malabsorption due to an intestinal, hepatic or pancreatic issues: Certain disorders that affect the body’s systems for absorption and metabolisation of nutrients (as in the case of Celiac disease), will make absorption of Vitamin D3 difficult to an acute level.
  • Excessive consumption of antibiotics: Pharmaceutical antibiotics can affect absorption through the intestines and destroy beneficial bacteria which are necessary for the digestion and assimilation of nutrients.

A lack of Vitamin D3 is becoming more and more prevalent these days. According to some nutritional experts, this is a problem of epidemic proportions, affecting the health of thousands, if not millions of people. Luckily, it is possible to increase our levels of colecalciferol in a safe and sensible way.

How can I increase my levels of Vitamin D3?

The cheapest and most effective way to increase your levels of Vitamin D3 is by exposing your skin to the sun. However, the amount of time a person needs to spend in the sun in order to achieve the RDI of Vitamin D3 will depend on the percentage of skin exposed and the age of the person, as can be seen in the following table:

Individual Amount of time spent exposed to direct sunlight to reach the RDI of vitamin D3
Young person, wearing winter clothes 40 minutes
Older person, wearing winter clothes 2 hours
Young person, wearing summer clothes 20 minutes
Older person, wearing summer clothes 1 hour
Young person, in bathing suit 10 minutes
Older person, in bathing suit 20 minutes

The table above is a very basic approximation and uses calculations for an average person who is thin, has white skin, who lives in a sunny climate and who is exposed to the stated sunlight at midday. Cloudy skies, a larger body mass, dark skin and the use of sunscreen are all factors which will require extra time spent exposed to sunlight. You should consult your health care professional for specific advice based on your actual needs.

However, excessive exposure to solar radiation will cause premature aging of the skin and increase the likelihood of developing melanoma or skin cancer. This is why many people prefer to avoid the sun’s rays altogether, making it even more critical for such individuals to obtain Vitamin D3 through their diets.

Vitamin D3 is absorbed more efficiently if it is accompanied by foods rich in fats.
(Source: Prokopenko: 50653501/

Which foods are Rich in Vitamin D3?

A diet rich in colecalciferol helps to avoid a deficiency of this vitamin, especially if the person is not getting enough exposure to sunlight. Oily fish (such as sardines, anchovies, salmon, trout and tuna) are the principal source of Vitamin D3. Dairy products also contain a high level of colecalciferol, which is vital part of a healthy diet.

The following table describes the food sources for Vitamin D3 and classifies each of them according to their concentration of colecalciferol. You may also review the percentage of the recommended daily intake (RDI) of Vitamin D3 which is provided by each of these products. All of these details should be used as a guide for the average adult.

Food Approximate concentration (IU) % RDI (for an adult)
Cod liver oil (1 tablespoon) 500 80
Salmon (75g) 350 60
Oysters (100g) 320 50
Mackerel (75g) 200 30
Tuna (75g) 150 25
Shrimp (100g) 150 25
Sardines (75g) 150 25
Milk (250ml) 100 15
Egg yolks (unit) 45 8
Calves livers (75g) 35 6
Margarine (1 tablespoon) 30 5
Cheddar cheese (100g) 25 4

The combination of a diet rich in Vitamin D3 and adequate exposure to sunlight will produce the best results for increasing reserves of colecalciferol. If these two methods are not sufficient to help you achieve the RDI of this nutrient, it could be time to start taking a Vitamin D3 supplement.

Who should take a Vitamin D3 supplement?

A colecalciferol deficiency could be affecting up 80% of the population. This is why so many experts recommend that everyone should be increasing their intake (with basic foods such as milk or eggs for example). However, the following groups of people will most benefit from an extra intake of Vitamin D3:

  • Adults over the age of 70
  • People on a vegan or vegetarian diet
  • People with inadequate exposure to direct sunlight 
  • Older women, especially those already at risk of osteoporosis
  • Individuals who are overweight or obese
  • People who regularly take antibiotics
  • People with illnesses that cause malabsorption (such as Crohn’s or Celiac disease)
  • Individuals who have undergone gastrointestinal surgery to aid weight loss (such as bariatric surgery)
  • People with hypertension, especially if they have been advised to control this illness with diet and exercise (without medication)
  • People with renal insufficiency

A recent German study made an unexpected finding, after providing two hundred men with Vitamin D3 supplements, when they observed a significant increase in the testosterone levels in individuals taking this supplement for one year. Therefore, colecalciferol may also be of benefit to men who want to increase their levels of testosterone.

Dr. Mark PorterDoctor and medical correspondent for The Times
“(…) almost all people under the age of 5 or over the age of 65, pregnant women, mothers who are breastfeeding and those who are not sufficiently exposed to the sun should consider taking a Vitamin D supplement”.

What benefits can I expect to see after taking a Vitamin D3 supplement?

After a few weeks of taking a Vitamin D3 supplement, you can expect to see an increase in energy levels and an improvement in your general mood. Months later, there will be an increase in mineralisation of the bones and a noticeable decrease in your risk of osteoporosis and fractures. Other beneficial effects will also appear, which we have summarised in the following list:

  • Increased muscle strength and endurance
  • Decrease in blood pressure with an improvement of cardiac health
  • Improvement of the health of teeth and gums
  • Improvement in immunity and lower incidence of infections
  • Reduced inflammation
  • Improvement in autoimmune disease symptoms, such as psoriasis
  • Increased production of testosterone in men
  • Increased insulin sensitivity and better blood sugar control
  • Lowered occurrence of certain types of cancer
  • Improvement in weight control

Some fitness enthusiasts use this supplement to gain muscle or to slim down. Although adequate levels of colecalciferol are essential for muscle development and reducing fat, no direct link has been found between taking these supplements and improving physical fitness.

How should I take a Vitamin D3 supplement?

Vitamin D3 supplements are easy to use and store. The manufacturer’s instructions contain all the necessary information needed to achieve an adequate supplementation. In the following paragraphs you can find answers to the most frequently asked questions about taking Vitamin D3 supplements, which may have ocurred to you while reading this article:

  • Should I take it with or without food? The absorption of Vitamin D3 supplements is highly elevated, regardless of whether it is taken with or without food. Being a liposoluble vitamin, its assimilation maybe be slightly enhanced if it is taken with fatty foods (fish, olive oil or dairy).
  • At what time should I take it? If the supplement is taken with the largest meal of the day (lunch or dinner), the fats present in the food will aid with absorption. In the long term, this can make colecalciferol supplementation up to 50% more effective.
  • What dose should I take? It is advised that you use a vitamin D3 supplement with a dose that can reach the RDI of 800-1000 IU. Taking over 3000-4000 IU per day puts you at risk of an overdose and the toxicity associated with an excess of Vitamin D3 in the body. This is why we strongly advise to never take more than the RDI.

Is it possible to take too much Vitamin D3?

If an excessive quantity of Vitamin D3 supplements are taken, for example, over 3000-4000 IU per day, this liposoluble vitamin will accumulate in the body’s tissues. This will increase the absorption of calcium which causes symptoms such as nausea, vomiting and diarrhoea. In the long run, this excess will cause more dangerous cardiac and cerebral side effects.

An excess of colecalciferol can cause an increase in calcium deposits. If this mineral builds up in blood cells, they will become rigid and increase the probability of developing hypertension and serious cardiovascular disease, such as myocardial infarction and stroke.

What contraindications do Vitamin D3 supplements have?

Vitamin D3 supplements can be freely bought and taken without a visit to the doctor. They are considered a safe product for human consumption. However, these supplements are not totally free from controversy. Colecalciferol supplements have been shown to cause undesired side effects in some people.

It is advised that people with a history of thrombosis, stroke or myocardial infarction take be careful with these supplements. Some studies have found data that seems to indicate a possible increase in the incidence of these diseases in certain people. This is most likely due to an increase in arterial calcification.

Vitamin D3 strengthens our teeth and bones.
(Source: Sadovnikova: 94387331/

It is also recommended that people with renal, hepatic or pancreatic metabolic issues (such as diabetes) consult with a health professional before they begin taking any D3 supplement. Pregnant or breastfeeding women should always seek medical supervision before using colecalciferol.

Did you know that the sunlight necessary to create Vitamin D3 on the surface of the skin is not able to penetrate through glass? This is why you can’t increase your levels of colecalciferol if your are only exposed to sunlight inside an office or a vehicle.

Shopping Criteria

If you want to benefit from everything that Vitamin D3 has to offer, while also protecting yourself from any undesired side effects, it is necessary to be careful when choosing a supplement. The following shopping criteria will help you to choose a product that is safe, effective and economical:

Suitable for Vegans and Vegetarians

If you are vegan or vegetarian, it can be very complicated choosing a Vitamin D3 supplement that is suitable for you. Most of these products are synthesised from fish oil, which is obviously an animal product. However, there are several types of genetically modified mushrooms and lichen capable of producing vegan colecalciferol.

Carefully read the label of the supplement before making your purchase. Look for the vegan quality seal and make sure it is a plant-based form of Vitamin D3.

You must check that your product contains colecalciferol and not ergocalciferol, a type of plant-based (but less potent) form of Vitamin D.


Although they are extremely rare, some secondary allergic reactions have been reported from taking Vitamin D3 supplements. People who are gluten- or lactose-intolerant, or who have less common allergies (such as allergies to fish oil), must be mindful when selecting a colecalciferol supplement.

If you suffer from a food intolerance, it is very important that you look for information about any allergens contained in the supplement by consulting the label.
(Source: Grigoreva: 43832150/

Contraindications With Other Medications

Vitamin D3 is a potent and highly effective nutrient. This makes it a substance that is capable of potentially reacting and interacting in various ways with many types of medications. If you are taking any of the following medicines, consult a health professional before beginning with a vitamin D3 supplement:

  • Antiepileptics and anticonvulsants
  • Treatment for a renal insufficiency
  • Statins
  • Corticosteroids
  • Antibiotics
  • Antiarrhythmic drugs
  • Treatment for hypertension
  • Diuretics
  • Laxatives

Combined with Vitamin K2

The main detractors of Vitamin D3 warn that this nutrient is potentially capable of producing a build up of calcium in the arteries, which over time, can result in the deterioration of blood cells. The predisposes the body to a range of serious life-threatening illnesses, such as myocardial infarction or stroke.

This debate is centered around whether these effects are due to excessive and prolonged supplementation over a long period of time, or if they can appear after only a short period of minimally effective use. If you are worried about this controversy, consider using a Vitamin D3 supplement combined with Vitamin K2. Vitamin K2 prevents the calcification of the arteries and increases the potency of the beneficial effects of colecalciferol.

How to take Vitamin D3

Vitamin D3 supplements can be purchased in many different forms. This can be as powder, tablet form, in soft capsules or even as a liquid. All of these D3 products are absorbed and function in a very similar way. However, some people incorrectly assume that products packaged as a spray, or as a liquid with a dropper, are less effective.

Vitamin D3 products that come in liquid form are the easiest to use. The number of drops of Vitamin D3 liquid formula indicated by the instructions are simply dropped directly on to the tongue. If the product is a spray, it can be sprayed in the mouth or even used on food as a type of seasoning.

Did you know that tinted windows can limit your body’s production of Vitamin D up to 97.5%?

Value for Money

If you would like to avoid spending a lot of money while supplementing your Vitamin D3 intake, choose a product that contains a moderate dose of the nutrient. Products that contain very high doses of Vitamin D3 increase the cost of the supplement, without necessarily enhancing its beneficial effect, and while also increasing the risk of negative side effects.

Alternatively, you can select a colecalciferol product that contains higher doses (greater than 4000 IU) and take the supplement on alternating days or even once a week. This is a safe and economical way to best take advantage of a Vitamin D3 product with an excessively high dose.


At the moment, Vitamin D3 deficiency is a real problem for the majority of the population. Our increasingly sedentary lifestyle, pollution, and widespread use of sunscreen has contributed to the lack of this critical nutrient in our bodies. The consequences to our general health and well-being can be dire.

A simple change of habits, while also adding a Vitamin D3 supplement to our diet, will help keep our bones, heart and brain in the best possible condition. Be sure to use this type of supplement prudently and with medical supervision, and the “vitamin of the sun” will keep osteoporosis at bay. Enjoy an active and healthy life with colecalciferol!!

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(Source of the featured image: Es75: 48065643/