Vitamin D

Testing Recommendations

Who should be screened for Vitamin D deficiency?

According to Canadian Vitamin D Guidelines, certain individuals are recommended to be tested for vitamin D levels. These groups included:

  1. Individuals with conditions affecting vitamin D absorption, such as celiac disease, Crohn's disease, and cystic fibrosis.

  2. Individuals with conditions that may cause an increased breakdown of vitamin D, such as certain liver or kidney diseases.

  3. People taking medications that could affect vitamin D metabolism, like anticonvulsants, glucocorticoids, and antiretroviral drugs.

  4. Individuals with osteoporosis or a history of low-trauma fractures.

  5. Older adults with a history of falls or fractures.

  6. Individuals with dark skin or those who wear concealing clothing for cultural reasons, as they may not receive adequate sun exposure to synthesize vitamin D.

  7. Obese individuals, as they may have lower levels of circulating vitamin D.


What is vitamin D, and why is it important?

Vitamin D is a fat-soluble vitamin that plays a crucial role in various functions within the human body. It is essential for maintaining strong bones, regulating calcium and phosphate levels, and supporting the immune system. Vitamin D can be obtained from sun exposure, food sources like fatty fish, fortified foods, and supplements.

When is vitamin D testing not indicated?

Vitamin D testing is not routinely recommended for the general population, as most people can maintain adequate vitamin D levels through diet, sun exposure, and supplements when necessary. Testing is typically reserved for individuals who are at higher risk of deficiency, such as:

  • People with malabsorption syndromes

  • Individuals with limited sun exposure

  • Elderly individuals

  • Individuals with dark skin

  • People who are obese or have undergone bariatric surgery

  • Patients with osteoporosis or other bone disorders

What is the difference between vitamin D2 and D3?

Vitamin D2 (ergocalciferol) and D3 (cholecalciferol) are the two main forms of vitamin D. Vitamin D2 is primarily found in plant-based food sources and fortified foods, while D3 is found in animal-based foods, supplements, and is synthesized in the skin upon sun exposure. Both forms are converted in the liver and kidneys into their active form, calcitriol, which can be utilized by the body. However, studies have shown that vitamin D3 is more effective in raising and maintaining blood levels of vitamin D.

How is vitamin D testing done?

Vitamin D testing is performed by measuring the concentration of 25-hydroxyvitamin D (25(OH)D) in the blood. This test reflects the combined intake of vitamin D from food, supplements, and sun exposure. The 25(OH)D test is a reliable indicator of a person's overall vitamin D status.

What are the optimal levels of vitamin D?

According to the Canadian guidelines, the optimal range for 25-hydroxyvitamin D (25(OH)D) is:

  • Sufficient: 50-125 nmol/L

  • Insufficient: 30-49 nmol/L

  • Deficient: less than 30 nmol/L

How can I ensure I am getting enough vitamin D?

To maintain optimal vitamin D levels, follow a balanced diet that includes vitamin D-rich foods, such as fatty fish, fortified milk, and eggs. Make sure to get sufficient sun exposure while taking care to protect your skin from sunburns. Supplements can also be used if recommended by a healthcare professional, especially for those at risk of deficiency.

Can I get too much vitamin D?

Yes, excessive intake of vitamin D can lead to toxicity, which can cause symptoms like nausea, vomiting, weakness, and kidney problems. The Tolerable Upper Intake Level (UL) for vitamin D is set at 4000 IU (100 mcg) per day for adults and children over 9 years old. For infants and younger children, the UL is lower.

What are the symptoms of vitamin D deficiency?

Symptoms of vitamin D deficiency can include fatigue, muscle weakness, bone pain, and an increased risk of fractures. In children, severe deficiency can lead to rickets, a condition characterized by soft bones and skeletal deformities. In adults, deficiency can lead to osteomalacia, a condition where the bones become soft and weak.

How long does it take to correct vitamin D deficiency?

The duration needed to correct vitamin D deficiency depends on the severity of the deficiency, the dose of supplementation, and individual factors such as age, body weight, and existing medical conditions. Generally, it can take several weeks to a few months of consistent supplementation to restore optimal vitamin D levels.

How much sun exposure is needed to produce adequate vitamin D?

The amount of sun exposure needed to produce sufficient vitamin D varies depending on factors such as skin type, geographical location, and time of year. Generally, exposing your face, arms, and legs to direct sunlight for 10-30 minutes, 2-3 times per week, is enough to maintain adequate vitamin D levels for most people. However, it is essential to balance sun exposure with skin protection to avoid the risk of skin cancer.

Can I get vitamin D from indoor tanning?

Indoor tanning can help produce vitamin D. However, the use of tanning beds is not recommended due to the increased risk of skin cancer associated with artificial UV radiation. A safer alternative is to obtain vitamin D from food sources, supplements, and moderate sun exposure.

Are there any medications that interfere with vitamin D absorption?

Yes, certain medications can interfere with vitamin D absorption or metabolism, such as anticonvulsants, glucocorticoids, and some HIV medications.

Can certain health conditions cause vitamin D deficiency?

Yes, some health conditions can lead to vitamin D deficiency by affecting absorption, metabolism, or utilization of the vitamin. These include gastrointestinal disorders like celiac disease, Crohn's disease, and cystic fibrosis, kidney and liver diseases, and obesity.

Can vitamin D help with depression or mental health?

Some studies and meta-analyses have explored the relationship between vitamin D levels and mental health, particularly depression. While there is some evidence suggesting that low vitamin D levels might be associated with an increased risk of depression, it is not yet clear whether vitamin D supplementation can effectively treat or prevent depression. More research is needed to establish a causal relationship and determine the appropriate treatment strategy.

Does vitamin D supplementation improve cardiovascular health?

The relationship between vitamin D levels and cardiovascular health has been the subject of numerous studies and meta-analyses. A meta-analysis published in JAMA Cardiology (2017) found that vitamin D supplementation did not significantly reduce the risk of major adverse cardiovascular events, such as heart attack, stroke, or cardiovascular death.xp

Can vitamin D reduce the risk of developing type 2 diabetes?

The association between vitamin D levels and type 2 diabetes risk has been investigated in several studies and meta-analyses. A meta-analysis published in The Lancet Diabetes & Endocrinology (2018) found that higher circulating levels of 25(OH)D were associated with a lower risk of type 2 diabetes. However, more research is needed to determine whether vitamin D supplementation can effectively prevent or treat type 2 diabetes and to establish the optimal dosage for this purpose.


[1] Autier P, Gandini S. Vitamin D supplementation and total mortality: A meta-analysis of randomized controlled trials. Arch Intern Med. 2007;167:1730–7





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