Vitamin D deficiency: symptoms and treatment

Vitamin D is essential for many processes in the body, from maintaining healthy bones and muscles to supporting the immune system. But vitamin D does not work entirely on its own. Magnesium plays an important role in helping the body activate and use it effectively. This close relationship raises important questions: How much vitamin D and magnesium do you actually need, what happens when vitamin D levels are too low, and how can a deficiency be corrected? In this blog, we explain the functions of vitamin D, its interaction with magnesium, recommended daily intakes, common signs and causes of vitamin D deficiency, and the steps you can take to maintain healthy levels.

Table of Contents

• What is vitamin D?
• How much vitamin D should I take?
• What are vitamin D deficiency symptoms?
• What are the causes of vitamin D deficiency?
  
• How can you fix a vitamin D deficiency?
• Vitamin D and Sunlight
• Vitamin Excess
• The interaction between vitamin D and magnesium
• Frequently asked questions

What is vitamin D?

Vitamin D is a fat-soluble vitamin that performs many important functions in the body. The human body can primarily produce vitamin D with the help of sunlight. UVB rays from sunlight stimulate the production of vitamin D in the skin, which is why sun exposure is considered the most important source of this essential vitamin. However, it is not always easy to get enough sunlight—especially in the winter months or in regions with low sun exposure, where supplements can be used. In addition to sunlight and supplements, there are also some foods that provide valuable amounts of vitamin D. Oily fish in particular, as well as egg yolks, cheese, and beef liver, contain small amounts of vitamin D (Harvard Health Publishing, 2021, Harvard T.H. Chan, 2023).

What is the difference between vitamin D and vitamin D3?

Both vitamin D2 and D3 are collectively referred to as “vitamin D.” This means that there is no difference between vitamin D and vitamin D3 in name. However, there is a difference between vitamin D2 and D3:

• Vitamin D2: Also known as ergocalciferol, this form is found in plant-based foods exposed to UV light, such as mushrooms. Vitamin D2 is cheaper to produce than D3 and is often added to products like milk, cereal, and orange juice.
• Vitamin D3: Also called cholecalciferol, this is the type of vitamin D produced in the skin of humans and animals when exposed to sunlight. Vitamin D3 is found in animal products such as mackerel, salmon, trout, tuna, beef liver, and eggs.

Supplements and fortified foods may contain either vitamin D2 or vitamin D3. Both forms are active and usable by the body. However, studies have shown that vitamin D3 increases blood levels of vitamin D more effectively and keeps them stable for longer (Tripkovic et al., 2012). For this reason, some experts prefer vitamin D3 over D2, as it is found in more foods and is naturally produced by the body.

What is vitamin D important for?

Vitamin D plays an important role in a wide range of functions and processes in the body, including:

• Cognitive health:
  Research shows that low blood levels of vitamin D are associated with cognitive decline. However, further studies are needed to determine the benefits of vitamin D supplementation for cognitive health (Mayo Clinic, 2023).
• Bone, muscle, and dental health:
  Vitamin D promotes the absorption of calcium and phosphate, which are essential for the health of bones, muscles, and teeth (NHS, 2020).
  Vitamin D significantly contributes to the prevention of osteoporosis, as it is essential not only for bone health but also for muscles that protect the skeletal system. Osteoporosis is a condition characterized by a decrease in bone density and deterioration of bone structure, leading to increased fragility and a higher risk of fractures. Women in menopause should pay particular attention to maintaining sufficient vitamin D levels, as decreasing estrogen levels increase the risk of bone loss and osteoporosis. A vitamin D deficiency can contribute to or worsen osteoporosis (Mayo Clinic, 2023; Mei et al., 2023)
  
• Support of the immune system:
  Studies show that a vitamin D deficiency may increase the risk of autoimmune diseases and infections (Aranow C., 2011).
• Mood regulation:
  Regarding vitamin D and its impact on mood and mental health, study results are currently inconsistent, and further research is needed (Huiberts, L. M., & Smolders, K. C., 2021). 
• Reduction of inflammation:
  Vitamin D has been shown to help reduce inflammation in the body. It lowers pro-inflammatory substances and increases anti-inflammatory substances, as demonstrated by a reduction in CRP levels (Krajewska, M., 2022).

How much vitamin D should I take?

The following table show the recommended daily intake for vitamin D. However, it is important to know your individual vitamin D level, as an overdose of these nutrients can be harmful. Generally, the daily requirement for vitamin D can be met through adequate sunlight exposure and a balanced diet. When taking supplements, caution is advised, and a doctor or nutritionist should always be consulted to avoid potential health risks.

The ideal amount of vitamin D can vary depending on age, sex, place of residence, season (and therefore sun exposure), and overall health status. However, there are general recommendations that can serve as a guideline.

Source: NIH, 2024

Would you like to check your vitamin D or magnesium levels?

With blood tests from Homed-IQ, you can receive detailed information about whether your levels are within the normal range or if you should take steps to improve your health. The Vitamin D Test and Magnesium Test allow you to check your values conveniently from home. Simply collect a small blood sample using a finger prick, send it by post to our ISO-certified laboratory, and receive the results in a clear and easy-to-understand lab report online.

Would you like to check more than just your vitamin D level? The Vitamin Deficiency Test measures the levels of vitamin D, vitamin B12, and folic acid (vitamin B9)—ensuring your body is supplied with all the essential vitamins needed to optimally support your health.

What are vitamin D deficiency symptoms?

• Children: Severe deficiency can cause rickets, with bowed bones, muscle weakness, bone pain, and joint deformities.
• Adults: Possible symptoms include fatigue, bone pain, muscle weakness or cramps, and mood changes such as depression.
• Mild deficiency: May cause weak or painful muscles.
• No symptoms: Vitamin D deficiency can also occur without noticeable signs.

Source: Cleveland Clinic, 2022

What are the causes of vitamin D deficiency?

Vitamin D deficiency can result from several factors:

• Low vitamin D intake or sun exposure: Not getting enough vitamin D through diet or sunlight.
• Reduced absorption:
  • Conditions such as weight-loss surgery.
  • Health conditions: Obesity, celiac disease, Crohn’s disease, cystic fibrosis, kidney disease, and liver disease can affect vitamin D levels or how the body uses vitamin D.
  • Certain medications: Steroids, laxatives, some cholesterol-lowering drugs, seizure medications, rifampin, and orlistat may lower vitamin D levels.
• Risk factors: Older age and higher levels of melanin in the skin can increase the risk of vitamin D deficiency.

Source: Cleveland Clinic, 2022

How can you fix a vitamin D deficiency?

Vitamin D deficiency is usually treated by increasing vitamin D levels and then maintaining them over time. This can include:

• Vitamin D supplements: Your healthcare provider may recommend vitamin D supplements, often vitamin D3, depending on your individual needs.
• Vitamin D-rich foods: Sources include fatty fish, egg yolks, mushrooms, liver, and cod liver oil.
• Fortified foods: Milk, plant-based milk alternatives, breakfast cereals, orange juice, and some dairy products may contain added vitamin D.
• Sun exposure: Sunlight helps the body produce vitamin D, but excessive unprotected sun exposure should be avoided because it increases the risk of skin cancer.
• Medical guidance: Speak with your healthcare provider to determine whether you need supplements and which dose is appropriate for you.

Source: Cleveland Clinic, 2022

Vitamin D and Sunlight

How is vitamin D produced in the body through sunlight?

Vitamin D is produced in the skin when it is exposed to sunlight. More precisely, it is the ultraviolet B rays (UVB) from the sun that stimulate this process. When the skin receives UVB rays, a substance called 7-dehydrocholesterol in the skin is converted into previtamin D3. Through a temperature-dependent process, this previtamin D3 is then converted into vitamin D3. However, the process is not yet complete, as the vitamin D3 formed in the skin is absorbed into the bloodstream and transported to the liver and kidneys, where it is finally converted into the active form, 1,25-dihydroxyvitamin D (calcitriol), which the body can then utilize (Bikle, 2021).

What factors influence vitamin D production?

Various factors affect how well our body can produce vitamin D from sunlight:

• Age: As we age, the skin produces less 7-dehydrocholesterol, which is needed for vitamin D production, making synthesis more difficult.
• Skin color: Darker skin contains more melanin, a pigment that protects the skin from sunlight. However, melanin also reduces the skin's ability to produce vitamin D. People with darker skin need to spend more time in the sun to produce the same amount of vitamin D as people with lighter skin.
• Season and time of day: Especially in winter, but also during early morning and late afternoon hours, the sun is weaker, and fewer UVB rays reach the skin, reducing vitamin D production.
• Air pollution and cloud cover: Polluted air and thick clouds can block UVB rays, reducing the production of vitamin D in the skin.

Source: Harvard Health, 2018

Vitamin Excess

Symptoms of Too Much Vitamin D

Vitamin D is important for your health, but taking too much through supplements can be harmful. Excess vitamin D may cause high calcium levels and lead to symptoms such as:

• Nausea
• Increased thirst and urination
• Poor appetite
• Constipation
• Weakness
• Confusion
• Balance or coordination problems
• Unclear speech

Source: Cleveland Clinic, 2022

What Causes Vitamin D Toxicity?

Vitamin D toxicity (hypervitaminosis D) is a rare condition caused by having too much vitamin D in your body. It usually results from taking excessive amounts of prescription or over-the-counter vitamin D supplements.

It’s rarely caused by food and cannot result from too much sun exposure. If you take vitamin D supplements regularly, periodic blood tests can help monitor your levels.

Source: Cleveland Clinic, 2023

The interaction between vitamin D and magnesium

In order for the body to properly use vitamin D, magnesium is essential. Scientific studies show that these two nutrients can influence each other. Vitamin D is mainly produced with the help of sunlight when it hits the skin. When UVB rays (ultraviolet rays) reach the skin, 7-dehydrocholesterol is converted into a precursor of vitamin D (pre-vitamin D3). However, this vitamin D is initially inactive and cannot yet be used by the body. It must first be converted into its active form in two steps: first in the liver, then in the kidneys. Magnesium plays a key role in activating vitamin D (Uwitonze, A. M., 2018). In one study, participants who received magnesium together with vitamin D showed higher serum levels of 25-hydroxyvitamin D (an intermediate form of vitamin D) compared to those who received only vitamin D (Cheung, M. M. et al., 2022). Only in its active form (1,25-dihydroxyvitamin D, also called calcidiol) can vitamin D fulfill its important functions and be properly utilized by the body—for example, by supporting the regulation of calcium and phosphate, which is crucial for bone health (NIH, 2021).

Frequently asked questions

Overview of magnesium

Magnesium is an essential mineral that performs numerous vital functions in the body. Since the human body cannot produce magnesium on its own, it must be obtained through food. Good sources of magnesium include almonds, soy milk, cooked spinach, brown rice, salmon, and bananas. In certain cases—such as one-sided diets or increased needs—taking supplements may be advisable to prevent a deficiency (Harvard T.H Chan, 2023).

What is magnesium important for?

Magnesium plays an important role in a wide range of functions and processes in the body. It is required for more than 300 biochemical reactions in the body. 

• Maintaining normal nerve and muscle function:
  Magnesium is important for the function of muscles and nerves, as it is involved in the transmission of nerve impulses and muscle contraction (Fiorentini D, 2021).
• Support of the immune system:
  Magnesium is essential for optimal immune function and the regulation of inflammation. A deficiency can lead to temporary or permanent impairments of the immune system (Ashique, S. et al., 2023).
• Maintaining a regular heartbeat:
  Magnesium plays a key role in regulating heart rhythm. Studies show that adequate magnesium intake is associated with a lower risk of cardiovascular disease (Fiorentini D, 2021).
• Bone health: Magnesium contributes to the formation and maintenance of bones by helping regulate calcium, which is important for bone density.
• Regulation of blood sugar levels:
  Magnesium influences insulin sensitivity and helps regulate blood glucose levels. A study showed that magnesium supplementation reduces insulin resistance and improves blood sugar control indicators in patients with type 2 diabetes (ELDerawi, W. A. et al., 2018).
• Support of energy and protein production:
  Magnesium is involved in more than 300 enzymatic reactions that contribute to energy production and protein metabolism in the body. It is especially important for the production and utilization of ATP (Tardy, A. L. et al., 2020).

Source: MedlinePlus, 2023

How much magnesium do I need?

The ideal amount of magnesium may vary depending on age, sex, activity level, diet, and overall health. Nevertheless, there are general guidelines that can be used as a reference.

Source: NIH, 2022

How does a vitamin D deficiency affect digestion?

A vitamin D deficiency can influence digestion via the microbiome. The microbiome consists of trillions of microorganisms in the intestine and is central to digestion and the immune system.

Studies have shown that vitamin D influences the composition of the microbiome. High vitamin D levels promote beneficial bacterial species such as Akkermansia and Bifidobacterium, which are important for healthy gut function, and reduce harmful bacteria. Vitamin D also appears to strengthen the intestinal barrier, which protects the body from harmful bacteria. A deficiency can weaken this barrier, increasing the risk of inflammation and contributing to digestive issues like constipation. Microbiome changes caused by a vitamin D deficiency can slow intestinal motility and impair nutrient absorption.

Quellen: Cleveland Clinic, 2024; Yamamoto & Jørgensen, 2020; Luthold et al., 2017; Singh et al., 2020

How does a vitamin D oversupply affect digestion?

Excess almost exclusively arises from excessive intake of supplements.

Elevated vitamin D levels can lead to hypercalcemia, as too much vitamin D increases calcium absorption in the intestines, resulting in elevated calcium levels in the blood. This can impair intestinal motility by disrupting nerve and muscle activity in the intestines, which may lead to constipation. Hypercalcemia can also interfere with water absorption in the intestines, making bowel movements more difficult and increasing the likelihood of constipation (Mayo Clinic, 2022).

Can the body produce vitamin D through a sunny window?

No, this is not possible. The sun emits different types of radiation, including UVA and UVB rays. While UVB rays are essential for vitamin D production in the skin, they cannot penetrate window glass. Windows filter out UVB rays, meaning vitamin D production through a closed window is not possible (NHS, 2024).

Can UVA rays penetrate window glass?

Yes, UVA rays are not blocked by window glass. However, this is not necessarily good news. These rays do not contribute to the production of vitamin D but are associated with skin aging. They can cause wrinkles and a loss of elasticity and contribute to the development of skin cancer types through indirect DNA damage in skin cells (Cleveland Clinic, 2022).

Interesting fact: Truck and long-haul drivers are especially at risk on the left side of their body, which is more exposed to UVA rays through the window while driving. Studies show that the left side of the face and the left arm are more prone to sun damage, resulting in a higher risk of skin cancers like melanoma and other types of skin cancer on those areas (DGUV, 2024).

What are the risks of UV radiation?

Both UVA and UVB rays from the sun can be harmful to the skin by causing sunburn, a skin inflammation, and contributing to premature skin aging. More importantly, UV rays are closely associated with the development of skin cancer, such as melanoma, a particularly aggressive form of skin cancer. Early skin damage significantly contributes to this risk. The more sunburns a person experiences throughout life, especially at a young age, the greater the risk of developing skin cancer. Repeated sunburns lead to an accumulation of damage in the skin, making it more vulnerable to cancerous changes (Cleveland Clinic, 2022; CDC, 2024).

Recommendations for sun exposure

The risks associated with UV rays therefore require a balance between ensuring sufficient vitamin D production and protecting the skin from sun-induced damage. To produce enough vitamin D, unprotected sun exposure of ideally 5–30 minutes daily or at least twice per week is recommended, depending on skin type and season. Shorter sun exposure times apply to people with lighter skin and during sunny seasons, while longer exposure is recommended for people with darker skin or during sun-poor seasons. After a short time in the sun, sunscreen should be applied to avoid sunburn and the associated risk of skin cancer. The sun protection factor (SPF) of a sunscreen indicates how long the skin is protected from sunburn. An sun protection factor of 15, for example, means that you can stay in the sun 15 times longer without burning than without protection (Raymond-Lezman& Riskin, 2023; NHS, 2022).

Note: SPF protects against UVB rays, but not directly against UVA rays. Therefore, it is important to choose a sunscreen labeled “broad-spectrum protection,” which blocks both UVA and UVB rays. Below, you will find more tips to help you protect yourself in the sun.

• Avoid direct sunlight between 11 a.m. and 3 p.m.
• Use sunscreen with SPF 30+ and UVA/UVB protection.
• Reapply sunscreen regularly.
• Wear sunglasses that offer 100% UVA/UVB protection.
• Protect yourself around reflective surfaces such as water and sand.
• Avoid tanning beds and artificial UV radiation.

Do I need extra vitamin D?

Most children and adults do not need extra vitamin D. Yet there are groups that do benefit from this (Dutch Journal of Medicine, 2012):

• Children from 0 to 4 years. Many children in this age group do not get enough vitamin D from their diet. In addition, it is  advised to protect young children as much as possible from the sun. Therefore, a daily supplement of 10 micrograms is recommended.
• Children and adults between the ages of 4 and 69 who have dark/tan skin that do not get enough sun during the day or wear clothing that covers their skin. A daily supplement of 10 micrograms is also recommended for this group.
• Women between the ages of 50 and 69. The advice of an extra 10 micrograms per day also applies here, as this improves bone density.
• Pregnant women. Sufficient vitamin D is extra important for this group. A deficiency can not only be detrimental to the woman, but also have serious consequences for a developing baby.
• Anyone 70 years and older. An extra 10 to 20 micrograms of vitamin D per day protects against bone fractures. Fair-skinned elderly people who get outside often can consume 10 micrograms per day.