Vitamin D is one of the micronutrients that attracts the most interest when we talk about health, nutrition and supplementation. It is commonly associated with bones, the immune system and even mood, but there are also many claims surrounding this vitamin that need to be put into context.
Understanding the benefits of vitamin D means knowing what functions it actually performs, where we can obtain it, the difference between vitamin D2 and vitamin D3, and in which situations supplementation may be worth considering.
As with other nutrients, having an adequate amount is important, but consuming more vitamin D than necessary does not necessarily mean obtaining greater benefits.
What is vitamin D?
Vitamin D is a fat-soluble vitamin that our body needs to perform different normal physiological functions.
Unlike most vitamins, it does not depend exclusively on food. Our body can produce vitamin D in the skin when it is exposed to certain types of ultraviolet radiation from sunlight.
However, the amount we can produce varies considerably depending on factors such as the time of year, latitude, age, skin pigmentation, clothing, the amount of time spent outdoors and other circumstances.
For this reason, when talking about vitamin D, we need to consider skin synthesis, diet and, when necessary, supplementation together.
What does vitamin D do?
Vitamin D is involved in many normal functions of the body.
Health claims authorised in the European Union include its contribution to:
- normal absorption and utilisation of calcium and phosphorus;
- normal blood calcium levels;
- the maintenance of normal bones;
- the maintenance of normal muscle function;
- the maintenance of normal teeth;
- the normal function of the immune system;
- the process of cell division.
These functions help explain why vitamin D appears so frequently in supplements associated with bones, physical activity and general well-being.
However, the fact that a nutrient contributes to a normal function does not mean that consuming additional amounts will continue to improve that function indefinitely.
Main benefits and functions of vitamin D
Contributes to the maintenance of normal bones
This is probably the best-known function of vitamin D.
Vitamin D contributes to the normal absorption and utilisation of calcium and phosphorus and to normal blood calcium levels.
This is directly related to its role in maintaining normal bones.
For this reason, when talking about bone health, we should not think only about calcium. Different nutrients contribute to the normal maintenance of bone tissue and need to be considered within our diet as a whole.
Contributes to the maintenance of normal muscle function
Vitamin D also contributes to the maintenance of normal muscle function.
This makes it particularly relevant when talking about physically active people, although it should not be interpreted as a claim that taking vitamin D will automatically increase strength or sports performance.
Improving physical fitness still depends on factors such as regular training, an adequate and balanced diet and proper recovery.
Contributes to the normal function of the immune system
Another recognised function of vitamin D is its contribution to the normal function of the immune system.
This has helped vitamin D gain even more popularity in recent years.
However, we need to distinguish between contributing to normal immune system function and claiming that taking vitamin D prevents or cures specific infections or diseases.
These are not equivalent claims.
Vitamin D is a nutrient required for normal body function, but no supplement should be presented as a substitute for medical prevention, diagnosis or treatment.
Plays a role in the process of cell division
Vitamin D also has a role in the process of cell division.
This function is less familiar to consumers than its relationship with bones or the immune system, but it reminds us that micronutrients often take part in much broader physiological processes than everyday advertising may suggest.
Where do we get vitamin D from?
We can obtain vitamin D mainly through three routes: production in the skin, certain foods and supplements.
Vitamin D production in the skin
Our skin can produce vitamin D3 when exposed to ultraviolet B radiation.
However, there is no universal amount of sun exposure that can be recommended to everyone in order to obtain a specific amount of vitamin D.
Production varies greatly depending on individual and environmental circumstances.
In addition, vitamin D should not be used as a reason to recommend excessive or unprotected sun exposure, as ultraviolet radiation can also damage the skin.
Vitamin D in food
Vitamin D occurs naturally in a relatively limited number of foods.
Its main dietary sources include:
- oily fish such as salmon, mackerel, sardines and trout;
- fish liver oils;
- egg yolk;
- some animal-based foods in smaller amounts;
- certain mushrooms, particularly when exposed to ultraviolet radiation;
- foods fortified with vitamin D.
The availability of fortified foods also depends on the country and the particular product, so it is always worth checking the label.
Vitamin D2 and vitamin D3: are they the same?
Food and supplements mainly contain two forms: vitamin D2, or ergocalciferol, and vitamin D3, or cholecalciferol.
Vitamin D2
Vitamin D2 can be found, for example, in certain mushrooms and may also be used in supplements and fortified foods.
It is a form capable of increasing vitamin D levels in the body.
Vitamin D3
Vitamin D3 is the form our body produces in the skin and is also found in certain animal-derived foods.
It is one of the most commonly used forms in food supplements.
Both vitamin D2 and D3 can increase vitamin D concentrations in the body, although the available evidence indicates that D3 may produce a greater increase and maintain those levels for longer.
This does not mean that we should choose a supplement simply because “D3” appears on the front of the packaging.
We should also check the amount provided, the daily serving, its source and the other ingredients.
Can vitamin D3 be plant-based?
Yes.
Although much of the vitamin D3 traditionally used in supplements comes from animal sources, vitamin D3 formulations obtained from lichen are also available.
This makes it possible to find options suitable for certain vegetarian or vegan diets.
For this reason, if the source is important to us, we should check the manufacturer's specific information rather than assume that all vitamin D3 comes from the same source.
How much vitamin D do we need?
EFSA has established an adequate intake for adults of 15 micrograms of vitamin D per day when minimal skin synthesis is assumed.
These 15 micrograms are equivalent to 600 international units, or IU.
The conversion is simple:
1 microgram of vitamin D = 40 IU.
This reference does not mean that everyone needs to obtain all 15 micrograms from a supplement.
The total amount of vitamin D available to our body also depends on other sources and individual circumstances.
What does vitamin D deficiency mean?
When assessing a person's vitamin D status, the main marker used is the blood concentration of 25-hydroxyvitamin D, or 25(OH)D.
However, interpreting the result is not simply a matter of comparing a number with a reference found online.
Different clinical criteria exist, and individual requirements can depend on each person's circumstances.
For this reason, if vitamin D deficiency is suspected or there are certain medical conditions or risk factors, a healthcare professional should assess whether a blood test is necessary and how the result should be interpreted.
We also should not assume that every healthy person needs regular vitamin D testing when there is no clinical reason to do so.
Who may be at greater risk of inadequate vitamin D levels?
There are certain circumstances in which maintaining an adequate vitamin D status may be more difficult.
These may include:
- very limited sun exposure;
- older age;
- certain conditions that make fat absorption more difficult;
- some digestive disorders;
- certain types of bariatric surgery;
- a diet very low in sources of vitamin D;
- certain medicines or medical circumstances.
This does not mean that everyone in one of these groups automatically needs supplementation.
It means that there may be a stronger reason to assess their status and individual requirements.
When may a vitamin D supplement be useful?
Supplementation may make sense when dietary intake and skin synthesis are not sufficient to meet requirements, or when there is a professional recommendation based on an individual's circumstances.
It may also be used to correct a diagnosed deficiency, but in that case the amount and duration of supplementation should be adapted to the specific situation.
Using a nutritional dose to complement the diet is not the same as using specific doses to correct a deficiency.
For this reason, we should not copy doses recommended to other people or assume that a higher amount is necessarily better.
Does more vitamin D mean more benefits?
No.
Vitamin D is fat-soluble and can accumulate in the body.
Excessive supplementation over time can raise blood calcium levels too much and cause adverse effects.
EFSA currently establishes a tolerable upper intake level for adults of 100 micrograms per day, equivalent to 4,000 IU.
This does not mean that 4,000 IU is a recommended dose for everyone.
It is a tolerable upper intake level for the general population, not a nutritional target.
In addition, in certain medical circumstances, a healthcare professional may use different protocols for specific periods precisely because these are carried out under supervision.
How to choose a vitamin D supplement
If we decide to use a supplement, it is worth checking more than just the words “vitamin D3” on the front of the packaging.
Check the amount
Vitamin D can be expressed in micrograms, international units or both.
Remembering that 1 microgram is equivalent to 40 IU makes it easier to compare different products.
For example, a supplement containing 25 micrograms provides 1,000 IU of vitamin D.
Check the daily serving
We should check whether the amount shown refers to one capsule, one gummy, one drop or the complete daily serving.
This is particularly important with products that require several units per day.
Check whether it contains other nutrients
Vitamin D is frequently combined with other micronutrients.
This does not automatically make the formula better or worse, but we should consider the complete formulation to avoid unnecessarily duplicating nutrients that we are already obtaining from other supplements.
As we saw when discussing the benefits of magnesium, reading the complete nutritional information is much more useful than looking only at the ingredient highlighted on the front.
Check the source if it matters to you
If we follow a vegetarian or vegan diet, it is worth checking the source of the vitamin D used.
Not all forms of D3 necessarily come from the same source.
When is the best time to take vitamin D?
There is no single mandatory time of day for taking vitamin D.
The most important thing is usually to maintain a routine that allows us to take the recommended dose correctly.
Because vitamin D is fat-soluble, its absorption may be favoured when fat is present in the intestine, so taking it with a meal containing some fat can be practical.
This does not mean that it needs to be taken with an especially high-fat meal.
Consistency, the correct dose and following the product instructions are much more important factors.
Vitamin D and exercise: what is the connection?
Vitamin D contributes to the maintenance of normal muscle function.
For this reason, maintaining an adequate nutritional status is also relevant as part of a physically active lifestyle.
But once again, we should avoid interpreting this function as a performance claim.
Taking vitamin D when we already have adequate amounts does not necessarily mean lifting more weight, running faster or recovering more quickly.
Performance depends on many factors, including training, nutrition, rest, hydration and planning.
Vitamin D, magnesium and other micronutrients
In nutrition, different vitamins and minerals often participate simultaneously in different processes.
This explains why some supplements combine several micronutrients within the same formulation.
At Green Folhas, for example, our Magnesium Glycinate Gummies also contain vitamin B6 and vitamin D3.
This can be convenient for people looking for a combined formulation, but we should always assess the complete composition and take into account any other supplements we are using.
Combining several products without checking their labels can result in unnecessarily duplicating certain nutrients.
Vitamin D and diet: context still matters
The attention given to supplements can sometimes make us forget that nutrition works as a whole.
Vitamin D is important, but we also need protein, fats, carbohydrates, minerals, other vitamins and a varied diet.
We saw something similar when looking at the benefits of omega-3: understanding a specific nutrient is useful, but we should not make it the absolute centre of our diet.
A supplement makes sense when it complements our diet and responds to a specific need, not when we try to use it as a substitute for healthy habits.
Vitamin D: necessary, without turning it into a miracle solution
The benefits of vitamin D are linked to important physiological functions.
It contributes to the maintenance of normal bones and muscle function, the normal function of the immune system and the normal absorption and utilisation of calcium and phosphorus, among other functions.
But this does not mean that taking high amounts will continue to improve our health indefinitely.
Supplementation can be very useful when there is a genuine need, insufficient intake or professional advice, but it should be used carefully.
Before choosing a product, it is worth checking whether it contains D2 or D3, how much it actually provides, the daily serving and which other nutrients are included.
And if a deficiency is suspected or there is a specific medical situation, the best decision is not to experiment with high doses but to have our status assessed by a healthcare professional.
Once again, supplementation works best when it is used to complement a balanced diet and healthy habits, rather than replace them.