Vitamin D holds a unique place in the Quebec nutritional landscape: unlike most vitamins whose intake depends mainly on food, vitamin D is largely synthesized by the skin under the action of the sun's ultraviolet B rays. However, at the latitude of Montreal—approximately 45° North—the solar incidence angle is insufficient to trigger significant skin synthesis of vitamin D between October and April, nearly half the year. Quebecers also spend most of their days indoors, cover their skin due to cold temperatures, and use sunscreens that block skin synthesis of vitamin D during sunny months. The result is not surprising: vitamin D deficiency is one of the most frequent nutritional deficiencies in Quebec, affecting, according to studies, between 30 and 50 % of the general population in late winter.
Clinique Omicron offers vitamin D testing as part of its medical collection services at several of its Quebec locations, with results interpreted by a physician and personalized supplementation recommendations. This article reviews the physiological roles of vitamin D, at-risk groups for deficiency in Quebec, symptoms that warrant attention, and current data on supplementation—dosages, forms, indications, and limitations.
Physiological roles of vitamin D: much more than bone health
Vitamin D is technically a prohormone rather than a vitamin in the strict sense—it undergoes double hydroxylation, first in the liver and then in the kidneys, to produce the biologically active form, calcitriol, which acts via nuclear receptors present in virtually all tissues of the body. Its classic role in regulating calcium and phosphorus metabolism is the best documented: it promotes intestinal absorption of calcium and phosphorus, regulates bone remineralization, and is essential for preventing rickets in children and osteomalacia in adults. In older individuals, severe vitamin D deficiency combined with insufficient calcium intake contributes to osteoporosis and fracture risk.
Beyond bone health, decades of research have identified vitamin D receptors in immune, muscle, cardiovascular, neural and pancreatic cells, suggesting extensive physiological roles well beyond the skeleton. Epidemiological associations have been documented between vitamin D deficiency and an increased risk of respiratory infections, autoimmune diseases, depression, type 2 diabetes, cardiovascular disease and certain cancers. However, the distinction between association and causation is crucial in medicine: it's possible that vitamin D deficiency is a marker of general ill-health - sedentary lifestyle, little sun exposure, poor diet - rather than a direct cause of these conditions. Randomized clinical trials of vitamin D supplementation have not demonstrated the spectacular benefits that observational studies would have led us to expect, which imposes a certain modesty in therapeutic claims.
Here are the groups at higher risk of vitamin D deficiency in Quebec: * **People with darker skin:** Melanin, the pigment that gives skin its color, reduces the skin's ability to produce vitamin D from sunlight. * **Elderly individuals:** As people age, their skin becomes less efficient at synthesizing vitamin D, and they may also spend less time outdoors. * **People who spend little time outdoors:** This includes those who work indoors, are homebound, or live in regions with limited sunlight, especially during Quebec's long winters. * **People who cover their skin for religious or cultural reasons:** Modest clothing that covers most of the skin limits sun exposure. * **People who consistently use sunscreen:** While sunscreen is important for preventing skin cancer, it also blocks UV rays necessary for vitamin D production. * **People who are obese:** Fat tissue can sequester vitamin D, making it less available for the body to use. * **People with certain medical conditions:** Conditions affecting fat absorption (like Crohn's disease, celiac disease, or cystic fibrosis) or the kidneys and liver (which convert vitamin D to its active form) can lead to deficiency. * **Individuals taking certain medications:** Some medications can interfere with vitamin D absorption or metabolism. * **Breastfed infants:** Human milk is low in vitamin D, so exclusively breastfed infants need vitamin D supplementation, especially if the mother's vitamin D status is low. * **People who consume very little vitamin D from their diet:** This includes those who avoid dairy products fortified with vitamin D or fatty fish.
Certain populations are at particularly high risk of vitamin D deficiency in Quebec and warrant systematic screening or empirical supplementation without waiting for test results. People over 65 years of age have reduced skin synthesis of vitamin D by about 75 % compared to young adults — their aged skin synthesizes vitamin D less effectively under the sun's action — are often less exposed to the sun due to reduced mobility, and have increased bone needs related to the risk of osteoporosis. Exclusively breastfed infants constitute a recognized risk group — breast milk is naturally low in vitamin D, which justifies the universal recommendation of supplementation with 400 IU per day from birth for all breastfed infants.
People with dark skin synthesize vitamin D less effectively under UV radiation due to melanin in the skin, which filters UVB rays. At the same latitude and sun exposure, a person with very dark skin can produce up to 6 times less vitamin D than a person with light skin. Individuals with intestinal malabsorption – such as Crohn's disease, celiac disease, bariatric surgery, or pancreatic insufficiency – absorb dietary and supplemental vitamin D less effectively. Obesity is associated with increased sequestration of vitamin D in adipose tissue, reducing its circulating bioavailability. People with very limited sun exposure due to their lifestyle – working night shifts, wearing concealing clothing for religious or cultural reasons – and those taking certain enzyme-inducing medications – such as antiepileptics or rifampicin – are also at high risk.
Vitamin D Supplementation: Doses, Forms, and Current Recommendations
The recommended form of supplementation is vitamin D3—cholecalciferol—which is better absorbed and more effective than vitamin D2—ergocalciferol—at raising and maintaining serum 25-OH vitamin D levels. Health Canada's current recommended dietary allowances are 600 IU per day for adults aged 1 to 70 and 800 IU per day for those over 70, with an upper safety limit of 4,000 IU per day for adults. However, many experts in preventive medicine and endocrinology believe these recommendations are insufficient to maintain optimal serum levels in Quebecers, especially in the absence of significant sun exposure, and empirically recommend doses of 1,000 to 2,000 IU per day for healthy adults living in Quebec.
When a significant deficiency is documented by blood test — a 25-OH vitamin D level below 30 nmol/L — a therapeutic loading dose is often prescribed: 50,000 IU of vitamin D3 weekly for 8 to 12 weeks, followed by a personalized maintenance dose, or a high-dose daily supplement under medical supervision. A follow-up test at 3 months is used to check for normalization of levels and adjust the maintenance dose. Vitamin D toxicity from excess is real but rare at commonly prescribed doses — it manifests as hypercalcemia which can cause nausea, vomiting, weakness, polyuria, and, in the long term, kidney calcifications. It generally only occurs at very high doses — above 10,000 IU per day for months — or in the presence of predisposing conditions such as sarcoidosis or certain lymphomas.
Frequently Asked Questions about Vitamin D in Quebec
Is the vitamin D test covered by the RAMQ in Quebec?
The 25-OH vitamin D dosage—commonly called a vitamin D test—is covered by the RAMQ under specific indications defined by the Drug Council and the RAMQ, particularly in the presence of recognized risk factors for deficiency: osteoporosis or fragility fractures, documented intestinal malabsorption (celiac disease, Crohn's disease, intestinal resection, bariatric surgery), chronic kidney failure, granulomatous diseases such as sarcoidosis, severe obesity, institutionalized elderly individuals, and at-risk infants. For healthy adults who wish to know their vitamin D level as a precaution or as part of a preventive check-up without a specific medical indication, the test is generally not covered by the RAMQ and is subject to private billing, with costs varying by laboratory. Clinique Omicron physicians can assess if your clinical situation meets the RAMQ coverage criteria during your consultation.
Should I take my vitamin D with food?
Yes — vitamin D is a fat-soluble vitamin, meaning it is absorbed with dietary fats. Taking your vitamin D supplement with a meal containing fat — even moderate amounts — significantly improves intestinal absorption. Studies have shown that taking vitamin D with the main meal richest in fat increased absorption by 50 % compared to taking it on an empty stomach. In practice, it is advisable to take your vitamin D supplement with dinner or supper rather than in the morning on an empty stomach. Taking it once a day is as effective as taking it in several divided doses, and some people prefer a weekly dose for ease of adherence — both approaches are equivalent in terms of biological efficacy.
Can I get enough vitamin D solely through diet in Quebec?
In practice, it is extremely difficult to achieve the recommended intake of vitamin D through diet alone in Quebec, particularly in the absence of significant sun exposure. Food sources naturally rich in vitamin D are few in number and rarely consumed in sufficient quantities: oily fish - salmon, mackerel, sardines, herring - cod liver, egg yolks. Foods fortified in Canada - milk, margarine, certain juices and vegetable drinks - provide modest quantities. A 250 ml glass of milk contains around 100 IU of vitamin D, which is a fraction of the 1,000 to 2,000 IU per day recommended by many experts for adult Quebecers. Supplementation is therefore virtually unavoidable for the majority of Quebecers during the winter months, and reasoned sun exposure - 15 to 30 minutes of sun on the arms and face between 10 a.m. and 3 p.m. in summer - represents the best natural source during the summer months, without sun protection for this short duration.
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