You’re doing everything right. Training consistently. Sleeping well. Eating clean. And yet, recovery feels slower than it should. Performance has plateaued. Your body feels heavier. Before you overhaul your training program or add another supplement to your toolbox, there’s one number worth checking: your vitamin D level.
For athletes and active people pushing hard, vitamin D deficiency is a silent performance thief. And in Canada, most of us are vulnerable without even knowing it.
The Hidden Deficiency
Here’s what the research shows: roughly 70 to 97 per cent of Canadians are vitamin D insufficient, especially from October through March. All because of geography. Canada sits above the 42nd parallel. From October through March, UVB radiation at our latitude is insufficient to trigger meaningful vitamin D synthesis in the skin, no matter how much time you spend outdoors.
What surprises most people is that athletes aren’t protected from this. In fact, research suggests active Canadians may be among the most vulnerable—especially those training indoors or at higher latitudes where winter darkness is most extreme.
Unless you’re intentionally seeking out dietary sources of vitamin D, most of us get only a fraction of what our bodies need to maintain optimal health and function. The result? Many athletes are training hard on an empty tank without knowing it.
Why This Matters for Performance
Vitamin D is not just a bone health nutrient. Vitamin D receptors exist in your muscle tissue, cardiovascular system, and immune cells, which means vitamin D’s impact on athletic performance goes way beyond what most people assume.
On muscle function and power output, the data is clear. Athletes with vitamin D levels at or above 125 nmol/L consistently demonstrate improved muscle strength, power, and overall physical performance compared to deficient counterparts. A study of professional soccer players found those with levels above 125 nmol/L had significantly better VO2 max and sprint performance than those with lower levels.
When it comes to injury risk, the numbers are hard to ignore. Research on NFL players is striking: those with vitamin D below 80 nmol/L experienced significantly higher muscle injury rates—26 per cent versus 12 per cent in players with adequate levels. For high-impact sports, low vitamin D is also associated with increased risk of stress fractures, a particular concern for athletes in running, jumping, and contact sports.
For immune resilience, athletes with adequate vitamin D experience fewer upper respiratory tract infections and recover more quickly during periods of intense training. For anyone whose season hinges on staying healthy during a key training block, this matters. And by helping to regulate inflammation, vitamin D plays a role in faster recovery between sessions—a quiet but meaningful edge over the long arc of a season.
Test. Supplement to a Target. Retest.
Here’s what stops most athletes: the “just take a supplement and hope” approach misses a critical point. Vitamin D requirements vary considerably between individuals based on body composition, skin tone, genetic background, and how much sun exposure you actually get.
Supplementing without testing is guessing.
A blood test or at-home test gives you an actual number. Once you know your baseline, you can supplement with a specific target in mind. Retest at 8 to 12 weeks and adjust accordingly. This feedback loop is what separates informed optimization from hope.
ImmunoCeutica’s immunology team recommends an optimal target of 125 to 250 nmol/L where research supports both immune resilience and athletic performance. For most Canadians, a maintenance dose of 1,000 to 2,000 IU daily is a reasonable starting point. But athletes with confirmed deficiency often need significantly more to reach optimal levels. Work with a healthcare provider to calibrate the right dose for your individual needs, body composition, and training demands.
Vitamin D is not a performance enhancer in the conventional sense. It won’t add watts to your FTP or shave seconds off your pace. It removes that invisible drag of deficiency that slows recovery, blunts immune function, and increases injury risk.
For active Canadians, particularly those training through fall and winter, knowing your vitamin D level is one of the most straightforward things you can do for your long-term health and performance.
Test. Supplement to a target range. Retest.
It really is that simple.
You may also like: Vitamin D
Read This Story in Our 2026 Summer & Outdoor Issue
Canada’s best source of health & fitness information — IMPACT Magazine’s 2026 Summer Outdoor Travel Issue: trail running, outdoor travel, workouts and seasonal recipes.
Featuring world-class French-Canadian ultra-trail runner Mathieu Blanchard, this digital edition takes you coast to coast through Canada’s most unforgettable bucket-list hikes, trail-running tips, and race-day strategies. Build strength and balance with targeted summer workouts, master the taper, and find your footing on technical terrain. Plus enjoy seasonal grilling and plant-forward recipes — Grilled Mexican Corn, Hoisin Portobello Burgers with Chili Lemon Broccolini, Smoky Black Bean Quinoa Burgers — and more outdoor cooking inspiration for active travelers.
