Low Vitamin D: Causes, Symptoms, and What to Do

Feeling tired frequently, noticing more intense muscle pain than usual, or having the sensation of lacking energy even after resting well are quite common situations nowadays. But this type of symptoms may be due to various causes. To stress, sleep, anxiety, diet, sedentary lifestyle… and also to low vitamin D levels.

In fact, many people discover they have low vitamin D levels almost by chance, after a routine blood work and not because they suspect a specific deficit.

In recent years, vitamin D has become one of the most reviewed parameters in medicine. And at the same time, it is also one of the nutrients about which the most information is published. 

Although we usually associate it only with bones, vitamin D also participates in related processes with the muscle function and the calcium metabolismAdditionally, its levels can vary significantly depending on various factors.

In this article, we will explore what it truly means to have low vitamin D levels, the most common causes, the symptoms that may arise, and what scientific evidence says about the most effective way to restore optimal levels.

What does it mean to have low vitamin D?

Unlike other vitamins, vitamin D it can be produced in the skin itself when we receive enough solar radiationWhen the skin receives enough UVB radiation (the part of sunlight that enables vitamin D production), a process begins that results in the generation of vitamin D3. This vitamin then undergoes various transformations in the liver and kidneys until it is converted into the form that typically appears in blood tests: 25-hydroxyvitamin D or 25(OH)D.

It is at this point where confusion usually begins. Because, although many people hear phrases like "I have low vitamin D," the reality is that there is no consensus on what the ideal level is for everyone.

Normal values and when to worry 

Thus, in 2011, Sai and colleagues analyzed the relationship between vitamin D, bone health, and a hormone called parathyroid hormone or PTH helps to maintain stable blood calcium levels. They observed that some bone-related markers were beginning to change, especially below approximately 20 ng/mL. Por eso, muchos consensos siguen considerando niveles por debajo de 20 ng/mL como déficit, mientras que cifras entre 20 y 30 ng/mL suelen interpretarse como insuficiencia.

However, this does not mean that a person with 28 ng/mL is "sick" or that someone with 19 ng/mL will automatically develop severe symptoms, as there are people with relatively low levels who feel perfectly fine and others who do experience symptoms with similar values.

That's why, interpreting a lab test always requires view the set:

• symptoms,

• sun exposure,

• diet,

• body composition,

• clinical context.

Most common causes of vitamin D deficiency

Lack of sun exposure

When talking about vitamin D, many people automatically think "get more sun." However, this simply isn't enough. The important thing is that it reaches enough UVB radiation to the skin, and that changes a lot depending on factors such as the time of year, the time of day, latitude, pollution, clothing, and actual exposure time.

One of the most important classic works on this subject was by Webb and her team in 1988. The researchers observed that in Boston, located at approximately 42º north latitude, during the winter months, practically no effective synthesis occurred of vitamin D3 in the skin.  

And the further north the population was located, the longer that “vitamin D winter” lasted.  On the other hand, in Edmonton, Canada, synthesis practically disappeared between October and March.  

This helps clarify something many people don't realize: you can live in a sunny country and still have low vitamin D levels. In practice, factors such as schedules, indoor work, actual time spent outdoors, and the amount of skin surface area exposed all play a role.

Why might I have low vitamin D levels even if I get sun exposure?

This is probably one of the most frequently asked questions, and it usually happens because “tomar el sol” no siempre significa producir suficiente vitamina D.

For example, many people go out early or in the late afternoon, when UVB radiation is much lower. Additionally, glass blocks a large portion of UVB, sunscreen reduces some of the synthesis, and in winter, production can drop significantly.

Added to that is the fact that no everyone responds the same way. La edad, la pigmentación de la piel o la composición corporal pueden hacer que dos personas que aparentemente “toman el mismo sol” tengan niveles completamente distintos.

Dark skin and cutaneous synthesis

The melanin, which is the pigment that gives skin its color, also acts as a kind of natural protection against solar radiation.

However, that protection also reduces part of the UVB radiation necessary to produce vitamin D. For this reason, people with darker skin usually need more time of sun exposure to generate similar amounts.

Obesity and body composition

Another important factor appears here: body composition. Vitamin D is a vitamin that the body primarily stored in fatty tissue, and that helps explain why people with obesity more frequently present with low levels.

In 2000, Wortsman and her team observed that individuals with obesity had lower circulating availability of vitamin D after UV exposure or taking supplements.

Within this framework, one of the main hypotheses being considered is that part of that vitamin D remains retained in the adipose tissue, reducing the amount circulating in the blood.

Vitamin D-deficient diet

Another factor to consider, which is quite common even with a relatively good diet, is that it is often difficult to reach high levels of vitamin D through food alone.

This usually happens because many people consume little oily fish or follow dietary patterns where vitamin D sources are scarce. For this reason, in practice, diet alone often it's not worth it low sun exposure.

Intestinal absorption issues

Vitamin D needs to be absorbed along with dietary fats some digestive issues can make it difficult maintain proper levels. Esto puede ocurrir, por ejemplo, en enfermedad celíaca, enfermedad inflamatoria intestinal, cirugía bariátrica o algunos trastornos pancreáticos y hepáticos.

Often, it's not that the person "doesn't take enough vitamin D," but rather that the body doesn't utilize it correctly.

Low vitamin D symptoms (in women and men)

One of the biggest problems with vitamin D is that its symptoms are usually very non-specific. For example, many people notice absolutely nothing, while others describe fatigue, muscle aches, a feeling of weakness, or discomfort that is difficult to explain.

Precisamente por eso es importante no caer en el error de atribuir cualquier síntoma automáticamente a la vitamina D.

Fatigue and tiredness

Fatigue is probably one of the most talked-about symptoms when a vitamin D deficiency occurs.

In 2016, Nowak and colleagues conducted a double-blind clinical trial in individuals with fatigue and low vitamin D levels. After supplementing with vitamin D3, the intervention group showed a significantly greater improvement in the subjective perception of fatigue compared to placebo.  

Now then, esto no significa que toda fatiga se explique por vitamina D baja. Fatigue can have many different causes. Sleep deprivation, stress, anxiety, anemia, hormonal issues, overworking, or simply a lack of rest can produce very similar symptoms. What some studies do suggest, however, is that when a real deficit exists, fixing it can help to improve symptoms in certain people.

Muscle and bone pain

Musculoskeletal pain also frequently appears associated with significant deficits.

In 2003, Plotnikoff and Quigley observed a very high prevalence of hypovitaminosis D in patients with musculoskeletal pain persistent and non-specific. Many of these patients had been experiencing chronic discomfort for some time without their vitamin D levels having been previously assessed.

This helps explain why some people describe diffuse pain, a feeling of stiffness, muscle discomfort, or increased physical sensitivity when levels are very low.

Muscle weakness and feeling of decreased performance

Vitamin D also plays a role in processes related to muscle function. Precisely for this reason, some people with significant deficits describe heavier legs, feeling of reduced strength, poorer recovery, or lower physical performance.

The evidence is not equally strong across all populations, but there is some relationship between significant deficits and poorer muscle function, especialmente en adultos mayores.

Mood swings

The relationship between vitamin D and mood remains highly debated. Existen estudios que encuentran asociaciones entre niveles bajos y síntomas depresivos, pero la evidencia sigue siendo muy heterogénea.

In other words: having low vitamin D levels does not automatically mean that it is the cause of an emotional or psychological problem.

High parathyroid hormone and low vitamin D: what is the connection?

When vitamin D levels drop too low, the body may absorb calcium from food less effectively parathyroid hormone, also called PTHH.

PTH, as previously mentioned, is a hormone whose primary function is maintain stable blood calcium levels. When the body detects that available calcium may be insufficient, it increases the release of this hormone to try to compensate for it.

The problem is that, if this situation persists for a long time, the body may begin to use part of the calcium stored in the bone to maintain normal blood levelsTherefore, significant vitamin D deficiencies can be associated with bone mass loss and alterations in mineral metabolism.

In the previously cited study by Sai et al., they observed precisely a clear inverse relationship between vitamin D and PTH, although they also noted that the exact thresholds varied considerably between studies.  

What happens if your vitamin D levels are very low?

When the deficiency is mild, many people do not even show clear symptoms. The major problems usually appear especially in severe and sustained deficits for quite some time.

In those situations, the following may appear bone pain, muscle weakness, persistent musculoskeletal discomfort, and metabolic disorders of football.

In some cases, it may appear osteomalacia, meaning the bone loses part of its proper mineralization and becomes more fragile, which can result in diffuse pain, discomfort when moving, a feeling of weakness, or an increased susceptibility to fractures. Furthermore, when vitamin D levels remain very low for a long time, the sustained increase in PTH can also promote bone loss.

How to increase vitamin D: habits and supplements

Responsible sun exposure

The sun exposure

The classic work by Webb and colleagues showed precisely that during certain months of the year, cutaneous synthesis can be practically non-existent in some geographical areas. That is why "going out for a bit" is not always enough.

Foods rich in vitamin D

The best dietary sources are usually fatty fish such as salmon, sardines, mackerel, or herring, as well as egg yolks and some fortified foods. Aun así, muchas personas tienen difícil cubrir requerimientos elevados solo mediante alimentación.

Vitamin D3 supplements

When a confirmed deficiency or high risk exists, supplementing can be a herramienta útil.

Evidence typically shows that vitamin D3 increases serum levels more effectively than vitamin D2. Furthermore, some practical details also appear to be important. Mulligan and Licata in 2010 observed that taking vitamin D with the main meal significantly increased circulating levels of 25(OH)D.  That is why it usually makes more sense to take it with meals that contain some fat.

It is also worth understanding that not everyone responds the same wayFactors such as obesity, intestinal absorption, adherence, or baseline levels can significantly affect the rate at which vitamin D levels rise.

Does it make sense to combine vitamin D with K2 or magnesium?

Vitamin D it is part of metabolic pathways where other nutrients also intervene, among them the magnesium. Additionally, some formulations combine vitamin D3 with vitamin K2 due to its relationship with calcium metabolism.

Even so, it is best to avoid simplistic messages such as "everyone needs vitamin K2." The actual need depends on individual context diet and the type of accessories used.

Common mistakes when supplementing with vitamin D

One of the most common mistakes is assuming that “more vitamin D is always better.” 

annual megadose of 500,000 IU of vitamin D increased the risk of falls and fractures in older women. This does not mean that vitamin D supplementation is dangerous, but rather that extremely high and poorly planned doses are not always beneficial.

It is also common taking supplements without blood tests, using excessive doses for months, or assuming that any symptom will improve by increasing vitamin D.

Ultimately, understand your levels to take better care of yourself

When there is a real and sustained deficiency over time, it can indeed influence bone health, muscle function, and how we feel.

Factors such as sun exposure, indoor work, the time of year, body composition, or certain digestive disorders can cause many people to have low levels without realizing it. That is why, rather than obsessing over a specific figure, the most useful approach is to evaluate the full context: symptoms, habits, lab results, and individual situation.

When there is a real need for supplementation, IVB Vitamin D3K2 could be the option to support the maintenance of adequate levels, combining vitamin D3 with vitamin K2—two nutrients involved in calcium metabolism and the maintenance of bone health. Available in capsules or spray to adapt the outlet to your needs. 

The key lies in doing it with judgment: checking levels, assessing the context, and choosing the appropriate guideline for each case.

Frequently Asked Questions (FAQ)

What are the most common symptoms of low vitamin D?

The most common symptoms are usually fatigue, muscle pain, weakness, and bone discomfort, although many people do not show clear symptoms.

What vitamin D level is considered low?

A deficiency is generally considered to be below 20 ng/mL of 25(OH)D.

Can low vitamin D cause fatigue?

It can contribute in some cases, especially when a real deficiency exists, although fatigue has many other possible causes.

¿Qué alimentos tienen más vitamina D?

The foods highest in vitamin D are typically fatty fish, egg yolks, and liver.

Can you have low vitamin D even if you get sun exposure?

Yes. Latitude, season, clothing, sunscreen, time of day, and actual exposure time all have a significant influence.

How long does it take for vitamin D levels to rise?

It depends on the dosage used, baseline levels, sun exposure, and individual absorption. It is typically re-evaluated after several weeks or months.

¿Es mejor vitamina D2 o D3?

Evidence typically shows that vitamin D3 increases serum levels more effectively.

Should vitamin D be taken with food?

It likely does have advantages, especially when paired with meals that contain some fat.

Can you take vitamin D every day?

Yes, many guidelines use daily doses. The appropriate amount depends on the individual context and analytical levels.

References

1. Bouillon R. Comparative analysis of nutritional guidelines for vitamin D. Nat Rev Endocrinol. 2017 Aug;13(8):466-479. doi: 10.1038/nrendo.2017.31. Epub 2017 Apr 7. PMID: 28387318.

2. Holick MF, Binkley NC, Bischoff-Ferrari HA, Gordon CM, Hanley DA, Heaney RP, Murad MH, Weaver CM; Endocrine Society. Evaluation, treatment, and prevention of vitamin D deficiency: an Endocrine Society clinical practice guideline. J Clin Endocrinol Metab. 2011 Jul;96(7):1911-30. doi: 10.1210/jc.2011-0385. Epub 2011 Jun 6. 

3. Mulligan GB, Licata A. Taking vitamin D with the largest meal improves absorption and results in higher serum levels of 25-hydroxyvitamin D. J Bone Miner Res. 2010 Apr;25(4):928-30. doi: 10.1002/jbmr.67. PMID: 20200983.

4. Nowak A, Boesch L, Andres E, Battegay E, Hornemann T, Schmid C, Bischoff-Ferrari HA, Suter PM, Krayenbuehl PA. Effect of vitamin D3 on self-perceived fatigue: A double-blind randomized placebo-controlled trial. Medicine (Baltimore). 2016 Dec;95(52):e5353. doi: 10.1097/MD.0000000000005353. Erratum in: Medicine (Baltimore). 2017 Jan 20;96(3):e6038. doi: 10.1097/MD.0000000000006038. PMID: 28033244; PMCID: PMC5207540.

5. Plotnikoff GA, Quigley JM. Prevalence of severe hypovitaminosis D in patients with persistent, nonspecific musculoskeletal pain. Mayo Clin Proc. 2003 Dec;78(12):1463-70. doi: 10.4065/78.12.1463. PMID: 14661675.

6. Sai AJ, Walters RW, Fang X, Gallagher JC. Relationship between vitamin D, parathyroid hormone, and bone health. J Clin Endocrinol Metab. 2011 Mar;96(3):E436-46. doi: 10.1210/jc.2010-1886. Epub 2010 Dec 15. PMID: 21159838; PMCID: PMC3047227.

7. Sanders KM, Stuart AL, Williamson EJ, Simpson JA, Kotowicz MA, Young D, Nicholson GC. Annual high-dose oral vitamin D and falls and fractures in older women: a randomized controlled trial. JAMA. 2010 May 12;303(18):1815-22. doi: 10.1001/jama.2010.594. Erratum in: JAMA. 2010 Jun 16;303(23):2357. PMID: 20460620.

8. Webb AR, Kline L, Holick MF. Influence of season and latitude on the cutaneous synthesis of vitamin D3: exposure to winter sunlight in Boston and Edmonton will not promote vitamin D3 synthesis in human skin. J Clin Endocrinol Metab. 1988 Aug;67(2):373-8. doi: 10.1210/jcem-67-2-373. PMID: 2839537.