Vitamin D Deficiency: Symptoms, Causes & How to Restore Healthy Levels

July 28, 2026

The Dubai is one of the sunniest cities in the world [1]. So it might surprise you to learn that vitamin D deficiency is one of the most common health concerns seen here, and one of the most frequently missed. For most people living in the region, the day looks something like this: an air-conditioned home, a drive or covered commute, eight or more hours in an office, and an evening largely spent indoors. The skin barely sees the sun at all, and the vitamin D it needs to produce simply does not get made.

The frustrating thing about vitamin D deficiency is that its symptoms look nothing like a deficiency. Feeling tired all the time, getting every cold that goes around, a low mood that will not shift, hair that seems thinner than it used to be: these are the kinds of things people write off as stress, ageing, or just life. Without a blood test, there is very little to suggest a missing nutrient is behind it all.

This guide covers everything you need to know about vitamin D deficiency: the signs and symptoms to look for, what causes levels to drop, how to read your test results, and the most effective ways to restore healthy levels and keep them there.

What Is Vitamin D and Why Does It Matter?

Vitamin D is an an essential, fat-soluble nutrient that functions as a hormone in the body [2]. Unlike most nutrients, it is not primarily obtained through food: the body produces it when UVB rays from sunlight hit the skin, triggering a conversion process that eventually produces the active form the body can use. This makes it unique among essential nutrients, and it also explains why deficiency can sneak up on people who think they eat reasonably well.

Vitamin D receptors exist in almost every cell in the body, which gives you some sense of how broadly it influences health. Its roles include:

· Calcium absorption and bone health: vitamin D is essential for the gut to absorb calcium properly. Without adequate vitamin D, bones become progressively weaker over time, increasing the risk of osteoporosis and fractures.

· Immune function: vitamin D helps regulate both the innate and adaptive immune response. Low levels are consistently associated with increased susceptibility to respiratory infections and slower recovery.

· Muscle function: vitamin D deficiency weakens muscles and impairs neuromuscular coordination. In older adults, this increases the risk of falls and fractures significantly.

· Mood and brain health: vitamin D receptors are found throughout the brain, including in areas involved in mood regulation. Deficiency is linked to depression, anxiety, and seasonal low mood.

· Cell growth and inflammation: vitamin D helps regulate cell division and suppress chronic low-grade inflammation, which is associated with a wide range of long-term conditions including heart disease, autoimmune disorders, and metabolic disease.

Because vitamin D touches so many systems at once, deficiency tends to produce a cluster of symptoms that can seem entirely unrelated, which is exactly why it so often goes unrecognised.

Dr Rahmana, GP at Smart Salem, says "vitamin D is so much more than just a nutrient, rather it works to regulate our energy, mood, and physical strength. When we run low, our bodies report symptoms like persistent fatigue, brain fog, and muscle weakness. Maintaining optimal Vitamin D levels is foundational to our health since it directly impacts on our immunity, bone density, and cellular function."

Vitamin D Deficiency Symptoms: What to Look Out For

One of the most important things to understand about vitamin D deficiency is that many people have none of the classic symptoms at all. Deficiency develops gradually, and the body adapts quietly for months or years before something noticeable emerges. When symptoms do appear, they tend to be diffuse and easy to normalise.

The most commonly reported vitamin D deficiency symptoms are [3]:

1. Fatigue and Low Energy

Persistent tiredness that does not improve with sleep or rest is one of the most frequently reported symptoms of low vitamin D, and one of the least likely to be connected to it. Fatigue has dozens of possible causes, which is precisely why the vitamin D link gets missed so often. Studies have found significant correlations between low vitamin D levels and self-reported fatigue, and many people report a meaningful improvement in energy once levels are restored.

2. Bone Pain and Muscle Aches

Vitamin D is essential for calcium absorption and the normal mineralisation of bone. When levels are low for a prolonged period, bone can become soft and painful, a condition known as osteomalacia in adults. The aching tends to be dull and deep, felt most often in the lower back, hips, legs, and ribs. General muscle discomfort and weakness are also common, and some people report an aching in the muscles that is hard to distinguish from fatigue.

3. Frequent Illness and Slow Recovery

Vitamin D plays a central role in modulating the immune response, particularly in the mucosal surfaces of the respiratory tract. People with low vitamin D levels get respiratory infections more frequently and tend to take longer to recover. Research has linked vitamin D deficiency to increased rates of colds, flu, and lower respiratory tract infections. If you find yourself getting every illness that comes around, it is worth checking your levels.

4. Low Mood and Depression

The relationship between vitamin D and mood is well established and clinically significant. Vitamin D receptors are present in the limbic system, the area of the brain most involved in emotional regulation. Deficiency has been associated with increased rates of depression, anxiety, and seasonal affective disorder. While it is not the only factor in mood, addressing low vitamin D is one of the more straightforward and often overlooked contributors to improved wellbeing.

5. Hair Loss

The link between vitamin D deficiency and hair loss is documented and, for many people, deeply personal. Vitamin D is involved in the regulation of the hair follicle cycle and plays a role in activating hair follicle cells during the growth phase. When levels are low, more follicles than usual can enter the resting phase simultaneously, causing a form of diffuse hair shedding known as telogen effluvium. Some research also links vitamin D deficiency to alopecia areata, though this relationship is more complex.

The good news is that hair loss linked to vitamin D deficiency is generally reversible. It takes time: most people notice improvement over three to six months of addressing their levels, with fuller recovery taking up to a year. This is also one of the reasons testing matters before supplementing speculatively, since hair loss has many possible causes (including iron deficiency and thyroid dysfunction) and identifying the right one makes treatment far more effective.

6. Impaired Wound Healing

Vitamin D plays a role in the skin's repair processes, including the production of compounds that help close wounds and fight infection at the site of injury. Slow healing of cuts, bruises, or skin infections can be a sign that levels are insufficient, though this tends to be more noticeable in people with more significant deficiency.

7. Brain Fog and Difficulty Concentrating

Cognitive symptoms including difficulty concentrating, mental sluggishness, and memory lapses have been reported in people with vitamin D deficiency, and some studies suggest an association between low levels and poorer cognitive performance. The relationship is still being studied, but enough people report improvement in mental clarity following correction of deficiency that it is worth noting.

Vitamin D Deficiency Causes: Why Are Levels So Low?

Vitamin D deficiency in the UAE is not simply a story about not getting enough sun. It is about a combination of lifestyle patterns, biological factors, and dietary limitations that make adequate vitamin D production difficult for most people, regardless of the climate they live in.

· Limited sun exposure: UVB light hitting the skin is the body's primary mechanism for making vitamin D. In practice, most people in the UAE spend the majority of their time in air-conditioned environments, cover up when they do go outside, and avoid the midday sun (which is when UVB is strongest) because of the heat. The result is that the skin rarely gets the exposure it needs.

· Darker skin tone: melanin, the pigment that gives skin its colour, absorbs UVB radiation and reduces how efficiently vitamin D is synthesised. People with darker skin tones need significantly more sun exposure to produce the same amount of vitamin D as someone with lighter skin. In a population as diverse as the UAE, this is a particularly important factor.

· Obesity: vitamin D is fat-soluble, which means it can become trapped in fat tissue and circulate in the blood at lower concentrations. People with higher body fat percentages consistently show lower vitamin D levels, even with comparable sun exposure or supplementation.

· Age: the skin's capacity to synthesise vitamin D in response to sunlight decreases with age. Older adults are significantly more vulnerable to deficiency for this reason alone, even if their lifestyle has not changed.

· Gut absorption issues: conditions that affect fat absorption, such as coeliac disease, Crohn's disease, or a history of bariatric surgery, can impair the body's ability to absorb dietary vitamin D and supplements, even at adequate doses.

· Low dietary intake: very few foods contain meaningful amounts of vitamin D naturally. The main sources are oily fish (salmon, mackerel, sardines, tuna), egg yolks, and liver. For most people, diet contributes only a small fraction of what the body needs.

· Breastfeeding without supplementation: breast milk contains very limited vitamin D. Breastfed infants who are not given a supplement are at significant risk of deficiency, particularly in a population where maternal deficiency is itself common.

Vitamin D Deficiency Levels: What Do the Numbers Mean?

If you have had a blood test for vitamin D, your result will show your serum 25-hydroxyvitamin D level, written as 25(OH)D. This is the most accurate measure of vitamin D status available. Results are reported either in nanomoles per litre (nmol/L) or nanograms per millilitre (ng/mL), depending on the laboratory.

Here is how the ranges are generally interpreted:

· Severe deficiency (below 25 nmol/L / 10 ng/mL): at this level, the risk of bone disease is significant. Rickets in children and osteomalacia in adults can develop. Therapeutic supplementation under medical supervision is needed.

· Deficiency (25-50 nmol/L / 10-20 ng/mL): symptoms are likely and supplementation is clearly indicated. Most people with results in this range will experience noticeable improvements in energy, mood, and immune function once levels are corrected.

· Insufficiency (50-75 nmol/L / 20-30 ng/mL): levels are below optimal and may be contributing to fatigue, immune vulnerability, and other symptoms. Supplementation and lifestyle changes are recommended.

· Sufficient (75-125 nmol/L / 30-50 ng/mL): generally considered adequate for most people and associated with normal bone health and immune function.

· Optimal (100-125 nmol/L / 40-50 ng/mL): many integrative and functional medicine clinicians aim for this range for broader health benefits, including immune regulation and mood support [4].

If you have received a letter or medical document referencing a vitamin D deficiency diagnosis, you may see the ICD-10 code E55 (vitamin D deficiency), with E55.9 used for unspecified vitamin D deficiency. These codes are administrative classifications used in medical records and insurance documentation.

The most important takeaway from all of this is that a blood test is the only way to know where your levels actually sit. Symptoms alone are not a reliable guide, both because they are non-specific and because some people feel very little even at quite low levels. Testing before supplementing is the only way to know what dose is appropriate and whether it is working.

How to Restore Healthy Vitamin D Levels

Restoring vitamin D levels involves three main levers: sunlight, diet, and supplementation. For most people in the UAE, supplementation will be the most effective and reliable of the three, but all three are worth understanding [5] [6].

Sunlight

The UAE sun is strong enough year-round to produce vitamin D, but the window of opportunity is narrow. UVB rays, which are the ones responsible for triggering vitamin D synthesis, are strongest between roughly 10am and 2pm. This is also the hottest and most intense part of the day, which makes prolonged exposure impractical for most people.

A realistic approach for lighter skin tones is around 10 to 20 minutes of direct sun exposure on the arms and legs, without sunscreen, two to three times per week. People with darker skin tones will need longer exposure to achieve the same effect. Even with consistent effort, many people in the UAE cannot generate enough vitamin D through sunlight alone, which makes supplementation necessary rather than optional for a significant proportion of the population.

Diet

Food is rarely enough to correct a vitamin D deficiency on its own, but including good sources regularly can support overall intake. The best dietary sources of vitamin D are:

· Oily fish: salmon, mackerel, sardines, and tuna are among the richest natural sources.

· Egg yolks: contain modest but meaningful amounts of vitamin D3.

· Liver: one of the most concentrated animal food sources, though it is also high in vitamin A, so should not be eaten in very large amounts.

· Fortified foods: some plant-based milks, breakfast cereals and orange juices are fortified with vitamin D, though the amounts vary significantly between products.

Think of diet as a supporting factor rather than a primary solution. It contributes to the picture but is unlikely to move the needle significantly if levels are already low.

H3: Supplementation

For most people with confirmed vitamin D deficiency in the UAE, supplementation is the most effective route to restoring levels. Here is what to know:

· Choose vitamin D3 (cholecalciferol): this is the form the skin produces naturally and the one shown to be most effective at raising blood levels. It is more bioavailable than vitamin D2 (ergocalciferol), which is the form found in some older supplements and fortified plant foods.

· Take it with fat: vitamin D is fat-soluble and absorbs significantly better when taken with a meal that contains some fat.

· Dose appropriately: maintenance doses for people with sufficient levels typically range from 1,000 to 2,000 IU per day. For correcting deficiency, higher therapeutic doses (often 4,000 IU or above) may be required and should be guided by a clinician based on your test result.

· Consider co-factors: vitamin D works alongside magnesium (required for vitamin D activation) and vitamin K2 (which helps direct calcium into bones rather than soft tissue). Some combination supplements include all three.

· Retest after two to three months: retesting confirms whether your levels have responded and allows your dose to be adjusted appropriately. Supplementing without follow-up testing means you are guessing at whether it is working.

A note of caution: vitamin D is fat-soluble [1], which means it accumulates in the body rather than being excreted like water-soluble vitamins. Very high doses taken without medical guidance can lead to toxicity, with symptoms including nausea, kidney problems, and dangerously elevated calcium levels. Testing before you start and monitoring during supplementation is the safe approach.

When to Get Your Vitamin D Levels Tested

Testing vitamin D levels is one of the more straightforward things you can do to get useful health information: a single blood draw, a clear number, and a clear action plan that follows from it. It is particularly worth prioritising if any of the following apply:

• You are experiencing persistent fatigue, low mood, hair loss, bone or muscle pain, or frequent illness, and have not identified a clear cause.

• You spend most of your time indoors, cover up significantly when outside, or actively avoid sun exposure.

• You have darker skin, are over 50, are pregnant or breastfeeding, or have a condition that affects fat absorption.

• You are already taking a vitamin D supplement and want to confirm whether your dose is appropriate and whether your levels have reached the sufficient range.

• You are planning a pregnancy. Vitamin D deficiency in pregnancy is linked to complications including gestational diabetes, pre-eclampsia, and low birth weight.

Vitamin D is included in Smart Salem's Premium Health Screening, which means it can be assessed alongside a full picture of your metabolic, cardiovascular, and hormonal health in a single appointment. If you want a more targeted test, it can also be requested as part of a focused panel.

Vitamin D Deficiency FAQs

How much sun do I need to maintain healthy vitamin D levels in the UAE?

For lighter skin tones, around 10 to 20 minutes of direct sun exposure on bare skin (arms and legs, without sunscreen) two to three times per week can support vitamin D synthesis [7]. People with darker skin tones need longer.

Does vitamin D deficiency cause hair loss?

Yes, there is a documented link. Vitamin D is involved in the hair follicle growth cycle, and deficiency can trigger telogen effluvium, a form of diffuse shedding. Hair loss linked to vitamin D deficiency is generally reversible with treatment, though it takes time: expect three to six months before noticeable improvement. Hair loss has many possible causes, so testing is important before attributing it to vitamin D alone.

Can I have vitamin D deficiency symptoms even if I spend time outside?

Yes. Sun exposure alone does not guarantee adequate vitamin D levels. Factors including the time of day, season, skin tone, clothing coverage, sunscreen use, and age all affect how much vitamin D the skin actually produces. Testing is the only way to confirm your status regardless of how much time you spend outdoors.

How long does it take to correct vitamin D deficiency with supplements?

With appropriate supplementation, most people see meaningful improvement in blood levels within eight to twelve weeks. Symptom improvement often follows, though this varies. Retesting after two to three months allows you to confirm progress and adjust your dose if needed.

Can too much vitamin D be harmful?

Yes. Vitamin D toxicity, while uncommon, can occur with very high supplemental doses taken over time [8]. Symptoms include nausea, excessive thirst, kidney issues, and elevated calcium in the blood. This is one of the main reasons testing before supplementing (and monitoring during) is recommended rather than simply taking a high dose speculatively.

Is vitamin D deficiency related to osteoporosis?

Directly, yes. Vitamin D is essential for calcium absorption, and without it the body cannot mineralise bone properly. Long-term deficiency contributes to lower bone density and, over time, increases the risk of osteoporosis and fractures. Vitamin D is an important but often overlooked part of bone health management.

Can children be vitamin D deficient in a sunny country?

Yes, and it is more common than many parents expect. Children who spend most of their time indoors, are predominantly covered when outside, or who are breastfed without supplementation are particularly at risk. Vitamin D deficiency in children can cause rickets, a condition involving softening and weakening of the bones. Supplementation for breastfed infants and children with limited sun exposure is routinely recommended.

Does vitamin D deficiency affect fertility?

Research suggests vitamin D plays a role in reproductive health for both men and women. Low levels have been associated with irregular menstrual cycles, reduced ovarian reserve, and poorer outcomes in assisted reproduction in women, as well as lower sperm quality in men. If you are trying to conceive, checking vitamin D levels as part of a broader pre-conception health assessment is a reasonable step.

Should I take vitamin D with food?

Yes. Vitamin D is fat-soluble and absorbs significantly better when taken alongside a meal that contains some fat. Taking it on an empty stomach or with a fat-free meal reduces how much your body can absorb. The timing of day does not matter: what matters is that there is fat present in the meal.