Vitamin D in Alberta: Why Winter Sun Isn’t Enough
From October to March, Alberta sunshine can’t make the vitamin D your body needs. Here’s what the research says, and what to do about it.
By Ignatius Anane-Ansah, pharmacist
If you live in Alberta, there’s a good chance your vitamin D is running low right now, even if you feel fine and spend time outdoors. It isn’t about effort. It’s geography.
Vitamin D helps your body absorb calcium for strong bones, and it plays a part in muscle function and your immune system. Your skin makes it when the sun’s UVB rays reach it. For half the year, though, the sun over Alberta sits too low in the sky for that to happen.
Alberta has a six-month “vitamin D winter”
In a well-known study, researchers exposed skin compounds to sunlight in Boston and Edmonton throughout the year. In Edmonton, sunlight produced no vitamin D at all from October through March, even on clear days. Calgary is only slightly further south and Fort McMurray is further north, so the picture is similar across the province.
It shows up in Canadians’ blood tests
Statistics Canada measures vitamin D in blood samples from people across the country. Roughly one in three Canadians falls below the level Health Canada considers adequate, and the share climbs to about 40% in winter.
Who is most likely to run low
Low vitamin D often has no obvious symptoms. When it does, it can look like tiredness, aching bones or muscles, or catching every cold that goes around. You’re more likely to be low if you spend most daylight hours indoors, have darker skin, are over 70, cover most of your skin outdoors, or carry extra body weight.
What supplements can do
Vitamin D is a cornerstone of bone health, which is why it’s recommended so widely. It may also support your defences: a large analysis of 25 trials in more than 11,000 people found that vitamin D supplements modestly lowered the risk of respiratory infections such as colds. The benefit was greatest in people who started out low and took it daily, rather than in large occasional doses.
Choose D3, not D2
Vitamin D comes in two forms. A review of randomised trials found that vitamin D3, the form your skin makes, raises blood levels more effectively than vitamin D2. Check that the label says D3 (cholecalciferol).
How much to take
Health Canada recommends 600 IU a day for most adults and 800 IU after age 70, with a safe upper limit of 4,000 IU a day from all sources. People who are already low often need more than the minimum to bring their levels up, and a blood test can tell you where you stand. The vitamin D3 in my Essential Seven provides 2,500 IU in one tablet a day, within the safe limit. Take it with a meal that contains some fat to help absorption.
If you have kidney disease, sarcoidosis or high calcium levels, or you take a thiazide diuretic (water pill), check with me before starting vitamin D.
Don’t forget magnesium
Your body needs magnesium to convert vitamin D into its active form, and many people don’t get enough magnesium. That’s one reason my Essential Seven pairs vitamin D3 with magnesium bisglycinate.
Products in this article
Heading into winter? Start with vitamin D3, or get all seven everyday basics in one order.
Sources
- Webb, Kline & Holick (1988). Influence of season and latitude on the cutaneous synthesis of vitamin D3. J Clin Endocrinol Metab.
- Statistics Canada. Vitamin D levels of Canadians, 2012 to 2013.
- Martineau et al. (2017). Vitamin D supplementation to prevent acute respiratory tract infections. BMJ.
- Tripkovic et al. (2012). Comparison of vitamin D2 and vitamin D3 supplementation in raising serum 25-hydroxyvitamin D status. Am J Clin Nutr.
- Health Canada. Dietary Reference Intakes tables.
- Essential nutrient interactions: does low or suboptimal magnesium status interact with vitamin D and/or calcium status? (2023). Advances in Nutrition.
