Vitamin D (25-OH Vitamin D)#

Vitamin D helps your body absorb calcium from food, keeps bones and teeth strong, and plays a role in muscle function and immune health. Your body makes vitamin D when sunlight hits your skin. You also get it from a few foods (fatty fish, fortified milk, eggs) and from supplements.

In Canada, low vitamin D is common because of long winters with limited sunlight, indoor lifestyles, and the use of sunscreen for skin-cancer prevention.

The standard vitamin D test is 25-hydroxyvitamin D (25-OH D, sometimes written 25(OH)D). It measures the storage form of vitamin D in your bloodstream and reflects your overall vitamin D status from sunlight, diet, and supplements combined.

A different test - 1,25-dihydroxyvitamin D - is rarely useful and is only ordered in specific kidney or calcium disorders.

• Vitamin D2 (ergocalciferol) comes from plant sources and is sometimes used in prescription replacement at very high doses.
• Vitamin D3 (cholecalciferol) is made in your skin and is the form in most over-the-counter supplements. D3 is somewhat better at raising and maintaining blood levels.

Most over-the-counter Canadian vitamin D supplements contain D3.

Choosing Wisely Canada and most Canadian guidelines recommend against routine vitamin D testing in healthy adults without symptoms or risk factors. The reasons:

• Testing the general population is expensive and rarely changes the recommendation (which is to take a daily supplement during winter)
• Vitamin D supplements at recommended doses are very safe and inexpensive
• Treating a slightly low level in someone without symptoms or bone disease has not been shown to improve long-term health

Many provinces do not cover vitamin D testing in healthy adults for these reasons.

Testing is reasonable if you have:

• Bone disease (osteoporosis, history of fragility fractures, osteomalacia)
• Conditions that affect absorption (celiac disease, inflammatory bowel disease, cystic fibrosis, prior gastric or intestinal surgery, including bariatric surgery)
• Liver or kidney disease severe enough to affect vitamin D activation
• Medications that lower vitamin D (long-term steroids, anti-seizure medications, certain HIV medications)
• Symptoms of severe deficiency (bone pain, muscle weakness, fragility fractures)
• Dark skin and limited sun exposure
• Strict avoidance of sun, including for cultural or medical reasons
• Older adults (especially over 70) who are housebound or institutionalized
• A history of falls or fractures
• Obesity (BMI over 30), as vitamin D is sequestered in fat tissue
• Pregnancy or breastfeeding in someone with the risk factors above

For most healthy Canadian adults, yes. Health Canada recommends 600 IU per day for ages 9 to 70 and 800 IU per day for adults over 70. Many clinicians recommend 1000 to 2000 IU per day for general Canadian adults, especially in winter. This is a safer and lower-cost approach than routine testing.

No. Vitamin D testing does not require fasting.

No - test on your usual routine. The goal is to see whether your current diet and supplement plan is keeping your level adequate. Stopping the supplement before the test will give an artificially low result and is not useful.

High-dose biotin (vitamin B7) supplements can interfere with vitamin D assays. Stop biotin at least 72 hours before testing.

Most cases of low vitamin D in healthy Canadians can be corrected with over-the-counter vitamin D3 supplements. A common approach:

• Insufficient (30 to 49 nmol/L): 1000 to 2000 IU of vitamin D3 daily
• Deficient (less than 30 nmol/L): 2000 IU daily for 2 to 3 months, then drop to 1000 to 2000 IU daily for maintenance

A rough rule of thumb: every 1000 IU per day raises your blood level by about 25 nmol/L over about 3 months.

Retest in about 3 months to confirm the level is in range.

See your family doctor or a walk-in clinic if:

• You have bone pain, muscle weakness, or unexplained fractures
• Your level remains low despite reasonable supplementation
• You have known absorption problems (celiac, Crohn's, prior bowel surgery)
• You have known kidney or liver disease

In these situations, the cause needs assessment beyond a simple supplement.

Most people with mildly low vitamin D have no symptoms. Severe deficiency can cause:

• Bone pain, especially in the lower back, hips, and ribs
• Muscle weakness, especially in the thighs
• Fragility fractures (broken bones from minor falls)
• In children, soft bones and bowed legs (rickets)
• In adults, soft weak bones (osteomalacia)

Vague tiredness alone is rarely caused by low vitamin D.

A level over 125 nmol/L is higher than needed but is usually not dangerous. Toxicity is rare and usually occurs only above 250 nmol/L, almost always from taking very high-dose supplements (well above 10,000 IU per day for months). Symptoms of toxicity include nausea, vomiting, weakness, frequent urination, and high blood calcium.

If your level is high, reduce or stop your supplement and retest in 6 to 12 months. If you have symptoms of toxicity or high calcium, see a clinician in person.

In summer (roughly May through September), about 10 to 30 minutes of midday sun on the arms and face a few times a week is usually enough for fair skin. People with darker skin need more sun exposure to make the same amount of vitamin D. In winter, the angle of the sun in Canada is too low for skin synthesis to occur reliably anywhere north of about Toronto's latitude.

Most Canadian adults benefit from a winter vitamin D supplement, regardless of summer sun exposure.

It is difficult to get enough vitamin D from food alone. The main sources are:

• Fatty fish (salmon, mackerel, sardines, tuna)
• Fortified cow's milk and plant-based milks (Canada requires vitamin D fortification of milk)
• Egg yolks
• Some mushrooms (especially if exposed to UV light)
• Cod liver oil

For most people, a small daily supplement is more reliable than relying on food.

No. Tanning beds raise skin cancer risk - including melanoma - significantly. The Canadian Cancer Society recommends against them. Vitamin D supplements are a safer and reliable alternative.

Many observational studies have found links between low vitamin D and various health conditions, but randomized trials of vitamin D supplementation have not shown clear benefit for preventing heart disease, cancer, depression, or COVID-19. Vitamin D is important for bone health and may have other benefits, but it is not a cure-all. Take a daily supplement if you are deficient or insufficient, and do not expect dramatic effects on energy, mood, or chronic disease.

Yes. Common ones:

• Long-term corticosteroid medication (oral steroid pills, used for autoimmune or inflammatory conditions)
• Some anti-seizure medications
• Some HIV medications
• Cholesterol-binding resins
• Weight-loss medications that block fat absorption

If you take any of these long-term, ask your clinician whether vitamin D testing or higher-dose supplementation is appropriate.

Not necessarily. Most Canadians get enough calcium from food (dairy, leafy greens, fortified plant milks). Adding calcium supplements is only recommended when dietary calcium is low and is generally not needed in healthy adults. Talk to your clinician before starting calcium supplements, especially if you have kidney stones or heart disease.

Yes. Health Canada recommends 600 IU per day during pregnancy and breastfeeding. Higher doses (up to 2000 IU per day) are also widely considered safe in pregnancy. If you have known deficiency, discuss higher doses with your obstetrical care provider.

Most provinces do not cover routine vitamin D testing in healthy adults. Coverage is usually available when there is a specific clinical reason (bone disease, malabsorption, certain medications). TeleTest will only order vitamin D as an insured test when there is a documented clinical reason. Otherwise, you can pay an uninsured fee at the lab.

Costs vary by lab. Contact your local lab for current pricing, or see your TeleTest booking confirmation for the price applied to your order.

Over-the-counter vitamin D3 supplements are inexpensive in Canada - typically $5 to $15 for a 6- to 12-month supply at 1000 to 2000 IU per day. They are available at any pharmacy or grocery store.