The Sunshine Vitamin: Why Vitamin D is Especially Important During the Winter Months in Canada

With reduced daylight hours and dropping temperatures, many Canadians across the country retreat indoors to escape the harsh winter cold. While this seasonal shift is natural, it can have unintended consequences for our health, particularly when it comes to vitamin D.
Vitamin D is unique that we can make it ourselves. It is often referred to as the “sunshine vitamin” because when exposed to the ultraviolet rays of the sun it stimulates the skin to produce vitamin D naturally. However, there are a number factors that can affect the amount of ultraviolet radiation we receive and therefore vitamin D production. Read on to learn more about vitamin D and why its importance becomes even more pronounced during the long Canadian winters.
What is Vitamin D and Why Do We Need It?
Vitamin D is a fat-soluble vitamin that has many different roles in the body such as:
- Vitamin D helps the body use calcium and phosphorus, to build and maintain strong bones and teeth. Not getting enough Vitamin D can cause calcium and phosphorus levels in the blood to drop, leading to calcium being pulled from our bones to help maintain stable blood levels. This can cause osteomalacia (softening of the bones) or osteoporosis (porous bones) in adults as well as rickets (softening of the bones/deformations of the skeleton) in children.
- Vitamin D contributes to proper muscle function which can help improve balance and prevent falls and fractures.
- Vitamin D also plays other roles in the body such as supporting a healthy immune system and glucose metabolism.
Why is Vitamin D Especially Important During Canadian Winters?
Vitamin D is unique that we can make it ourselves. It is often referred to as the “sunshine vitamin” because when exposed to the ultraviolet rays of the sun it stimulates the skin to produce vitamin D naturally. However, there are a number factors that can affect the amount of ultraviolet radiation we receive and therefore vitamin D production such as:
- Latitude: many Canadians live above 42°North (i.e. Toronto 43°North) where little or no vitamin D can be produced from about November through February/early March and moving further north, for example Edmonton 53°North, the “vitamin D winter” extends from about mid-October to mid-March
- Season: the sun’s rays are weaker during the fall and winter
- Clothing: heavy clothing that inhibits sun exposure can also block synthesis
- Time of day: the sun is stronger between 10 AM and 3 PM
- Cloud cover or smog: for example, complete cloud cover reduces ultraviolet radiation
- Age: as we age our ability to synthesize vitamin D decreases
- Skin pigmentation: vitamin D synthesis in darker pigmented skin is reduced and takes a longer time
- Sunscreen use: can block vitamin D synthesis
How to Maintain Healthy Vitamin D Levels – Especially in Canadian Winters
Since in Canada we don’t get as much sun as we need to produce adequate vitamin D, as well as the many factors that can affect how much vitamin D your skin can make, the best way of getting adequate vitamin D is through both diet and supplements.
Dietary Sources
Vitamin D is found naturally in only a few foods such as fatty fish like salmon (394 international units (IU) per 75 grams sockeye salmon) and egg yolks (32 IU per yolk). The major sources of vitamin D in the Canadian diet come from fortified foods. Fluid milk, many plant-based beverages (i.e. soy, almond, rice beverages) and some calcium-fortified orange juices are fortified with vitamin D (100 IU per cup). Cheese and yogurt can be made with vitamin D-fortified milk; however, they do not contain as much vitamin D as fluid milk.
Supplementation
A variety of supplements are available on the market in various potencies, commonly ranging between 400 IU – 1000 IU.
How Much Vitamin D Do We Need?
Health Canada recommends different vitamin D daily intakes based on age and gender. The recommendations are based on maintaining bone health and have been set assuming minimal sun exposure. This is due to concerns about skin cancer from ultraviolet radiation from the sun.
Age Group | Recommended Intake Per Day | Safe Upper Limit |
Children 1-3 years | 600 IU | 2500 IU |
Children 4-8 years | 600 IU | 3000 IU |
Children 9-18 years | 600 IU | 4000 IU |
Adults 19-70 years | 600 IU | 4000 IU |
Adults > 70 years | 800 IU | 4000 IU |
Pregnancy & Lactation | 600 IU | 4000 IU |
Source: Institute of Medicine (IOM). Dietary reference intakes for calcium and vitamin D. Washington, DC: The National Academy Press, 2011.
Health Canada also recommends that people over the age of 50 years take a daily vitamin D supplement of 400 IU.
How is Vitamin D Status Measured and How Do We Know If We Are Getting Enough?
Vitamin D status can be measured in two ways:
- Vitamin D dietary intakes
- Vitamin D blood levels
Since Vitamin D can also be produced when skin is exposed to sunlight, it is the blood level data that gives a true picture of the vitamin D status in the body, reflecting total vitamin D exposure from foods, supplements, and synthesis in the skin from sun exposure.
When examining vitamin D blood levels, it is serum concentrations of 25-hydroxy vitamin D that is measured in the blood and different cut points for serum 25-hydroxy vitamin D have been established.
If you are concerned you are getting too little – or too much vitamin D, speak with your doctor about getting your blood level tested and determine if vitamin D supplementation is right for you.