Vitamin D3
Also called: cholecalciferol, D3, sunshine vitamin, D2 (ergocalciferol).
A fat-soluble vitamin whose status drops in winter in Canada, with two forms, two units and an upper limit that is easy to exceed.
What it is
Vitamin D enables active absorption of calcium in the gut and maintains blood calcium levels. The skin makes it under UVB rays, which depends on the season, time of day, day length, cloud cover, pigmentation and sunscreen. It is one of the few supplements Health Canada explicitly recommends.
What the label does not say
- Two units circulate on labels: 1 mcg equals 40 IU. A product showing 25 mcg and another showing 1,000 IU give you the same thing.
- The Health Canada monograph for products above 1,000 IU caps at 62.5 mcg (2,500 IU) per day for adults 18 and over, and asks you to consult beyond 6 months of use. The upper limit in the dietary reference intakes, by contrast, is 100 mcg (4,000 IU).
- A dry tablet swallowed on an empty stomach is not equivalent to a dose taken with a meal: dietary fat improves absorption.
- Statistics Canada reports that the proportion of Canadians below 30 nmol/L of 25(OH)D doubles during the winter months: 13% from November to March versus 5% from April to October (Canadian Health Measures Survey, 2016 to 2019).
The forms on the shelf
- D3 (cholecalciferol) and D2 (ergocalciferol): the two sources Health Canada permits in natural health products.
- The NIH indicates that D3 raises serum 25(OH)D more than D2 does and keeps those levels up longer.
- Oil-based drops, softgels or dry tablets: the NIH notes that the presence of fat in the gut improves absorption, even though some is absorbed without fat.
Published reference values
- Recommended intake: 15 mcg (600 IU) per day from 19 to 70, 20 mcg (800 IU) after 70. These values assume minimal sun exposure.
- Health Canada also recommends a supplement of 10 mcg (400 IU) per day from age 51 onward, and for anyone who does not eat foods containing vitamin D every day.
- Upper limit: 100 mcg (4,000 IU) per day for adults. The NIH considers signs of toxicity unlikely below 250 mcg (10,000 IU) per day, with toxicity occurring through hypercalcemia.
- NIH blood markers: deficiency below 30 nmol/L, insufficient intake from 30 to under 50 nmol/L, sufficiency at 50 nmol/L and above, possible adverse effects above 125 nmol/L.
When
With a meal containing fat. In Quebec, November to March is the period when skin synthesis is lowest.
Keep apart from
- Orlistat: reduces absorption of vitamin D from food and supplements. The exact spacing is not quantified in the NIH fact sheet.
- Calcium: vitamin D increases calcium absorption, so taking both adds to your calcium intake, which counts toward the upper limit of 2,500 mg per day.
To mention to a professional
- Hypercalcemia or hypercalciuria (a contraindication according to Health Canada), kidney disorder, use of antacids, anticonvulsants, corticosteroids, statins or thiazide diuretics, pregnancy and breastfeeding: check with a health care professional.
From the plate first
Egg yolk and fatty fish (salmon, Arctic char, rainbow trout). In Canada, milk, soft margarine and fortified plant-based beverages provide it too.
Sources
- NIH Office of Dietary Supplements, Vitamin D (Health Professional)
- Health Canada, Vitamin D
- Health Canada, natural health product monograph, Vitamin D (more than 1,000 to 2,500 IU)
- Statistics Canada, Vitamin D levels as we approach the shortest day of the year (CHMS 2016 to 2019)
Educational information, drawn from the sources above. It does not replace the advice of a health professional, who remains the reference for your situation, your medications, pregnancy or breastfeeding.