Vitamin D in Canada: Why Winter Sunlight Isn't Enough, and How Much You Need
Short answer: in most of Canada the winter sun is too low in the sky for your skin to make vitamin D. A classic study found no vitamin D production from sunlight in Edmonton (52°N) from October through March, and none in Boston (42°N) from November through February, and nearly all of Canada lies north of Boston. Health Canada's Recommended Dietary Allowance (RDA) is 600 IU (15 mcg) a day for ages 1 to 70 and 800 IU (20 mcg) after 70, with a tolerable upper intake level of 4,000 IU (100 mcg) a day for anyone 9 and older. Health Canada also advises a daily 400 IU supplement for adults over 50 and for breastfed babies.
Why winter sunlight isn't enough in Canada
Your skin makes vitamin D when ultraviolet B (UVB) rays reach it. In winter at northern latitudes, the sun sits so low that the atmosphere filters out most UVB before it reaches the ground. In a 1988 study, Webb, Kline and Holick exposed skin samples to sunlight on cloudless days and measured how much previtamin D3 formed:
| Location (latitude) | Months with no vitamin D production from sunlight |
|---|---|
| Edmonton (52°N) | October through March |
| Boston (42°N) | November through February |
| Further south (34°N and 18°N) | Production continued even in mid-winter |
Canada's southernmost point is just under 42°N, and cities such as Toronto, Montréal, Vancouver, Calgary and Winnipeg are all further north than Boston. The further north you live, the longer this "vitamin D winter" lasts. That is why food and, for many people, a supplement matter more here between fall and spring. The study measured skin samples on clear days, so cloud cover, clothing and time spent indoors only reduce real-world production further.
How much vitamin D do you need?
Health Canada uses the Dietary Reference Intakes set with the U.S. Institute of Medicine in 2010. The RDA is the daily amount that meets the needs of almost everyone in a group (about 97.5%). The tolerable upper intake level (UL) is the highest daily intake from all sources (food plus supplements) that is unlikely to cause harm; it is a ceiling, not a target. 1 mcg of vitamin D equals 40 IU.
| Age group | RDA (or AI) per day | Upper limit (UL) per day |
|---|---|---|
| Infants 0–6 months | 400 IU (10 mcg)* | 1,000 IU (25 mcg) |
| Infants 7–12 months | 400 IU (10 mcg)* | 1,500 IU (38 mcg) |
| Children 1–3 years | 600 IU (15 mcg) | 2,500 IU (63 mcg) |
| Children 4–8 years | 600 IU (15 mcg) | 3,000 IU (75 mcg) |
| Ages 9–70 | 600 IU (15 mcg) | 4,000 IU (100 mcg) |
| Over 70 | 800 IU (20 mcg) | 4,000 IU (100 mcg) |
| Pregnancy and breastfeeding | 600 IU (15 mcg) | 4,000 IU (100 mcg) |
*For infants the value is an Adequate Intake (AI), because there is not enough data to set an RDA.
Health Canada's practical advice
- Breastfed babies: a daily 400 IU (10 mcg) vitamin D supplement for infants and young children who are breastfed or receive breast milk. Babies fed commercial infant formula do not need one, because formula already contains vitamin D.
- Ages 2 to 50: include a daily source of vitamin D, from food or a supplement.
- Over 50: take a daily 400 IU (10 mcg) vitamin D supplement in addition to food.
In Canada, vitamin D products of up to 2,500 IU per dosage unit (or with a maximum recommended daily intake of 2,500 IU) can be sold without a prescription. Higher-strength products need a prescription.
Food sources of vitamin D
Very few foods contain vitamin D naturally, so most of what Canadians get from food comes from fortified products.
| Food | Natural or fortified | Notes |
|---|---|---|
| Fatty fish such as salmon, arctic char and rainbow trout | Natural | One of the few natural sources |
| Egg yolks | Natural | Contains some vitamin D |
| Cow's milk | Fortified | Fortification is required in Canada |
| Soft margarine | Fortified | Fortification is required in Canada |
| Unsweetened fortified plant-based beverages | Fortified | Check the label: not every plant drink is fortified |
Health Canada has also moved to allow higher vitamin D levels in milk and margarine, but for many people, especially in winter or if they do not drink milk, food alone may not reach the RDA.
Choosing a vitamin D supplement
- Check the NPN and the amount per dose in IU or mcg. Our guide How to Read a Natural Health Product Label in Canada shows where to find them.
- Count every source. Multivitamins, calcium combinations and fish liver oils often contain vitamin D too, and the UL applies to the total.
- Match the format to the person. Tablets and softgels give a fixed daily dose; drops suit babies and anyone who dislikes pills.
Examples in stock at Healthy Hub: Webber Vitamin D3 1000 IU, 260 Tablets, Jamieson Vitamin D3 1,000 IU, 200+40 Tablets and, for breastfed babies, Baby Ddrops 400 IU. See the full range in our Vitamin D collection, and read How Much Vitamin D3 Do Canadians Actually Need? and why vitamin D3 and K2 are often paired.
When to see a doctor or pharmacist
Talk to your doctor before taking more than the UL for your age, or if you have kidney disease, a history of kidney stones, a condition affecting fat absorption, or take medicines that interact with vitamin D. A blood test is the only way to know your vitamin D level. Ask a pharmacist which dose and format suit a baby, a child, or someone who is pregnant or breastfeeding.
Sources
- Webb AR, Kline L, Holick MF. Influence of season and latitude on the cutaneous synthesis of vitamin D3. J Clin Endocrinol Metab. 1988;67(2):373–378. PubMed 2839537.
- Health Canada. Notice: Prescription Drug List (PDL): Vitamin D (RDA and UL table by age; 2,500 IU non-prescription limit).
- Health Canada. Dietary Reference Intakes tables.
- Health Canada. Vitamin D (food sources, fortification).
- Health Canada. Applying Canada's Dietary Guidelines: Advice on vitamin and mineral supplementation (ages 2–50 and over 50).
- Health Canada. Nutrition for Healthy Term Infants: Recommendations from Six to 24 Months (400 IU for breastfed infants).
This guide is general information, not medical advice. Ask your pharmacist or doctor about your own situation.