Summer Sun and Vitamin D - What New Research Says Canadians Need to Know
- Summer sun isn't fixing your vitamin D - new research confirms it for many Canadians
- Stopping your supplement in summer is a common mistake with real consequences
- The only way to know your levels is to test
Every summer, a familiar assumption takes hold: I'm outside more, so my vitamin D levels must be fine.
It's a reasonable thought. And it's wrong for a significant number of Canadians - including many who would never guess they have a problem.
New research published in the European Journal of Clinical Nutrition (Newcastle University, June 2026) followed nearly 300 people across northern Britain over multiple seasons. The finding that made headlines: for older adults and people with darker skin tones, vitamin D levels did not improve meaningfully during summer - even with regular sun exposure.
The researchers were direct about the implications. If you are in a higher-risk group, you cannot assume that spending more time outdoors in summer will solve the problem.
Canada's geography makes this even more relevant than it might seem from a British study.
Why the Summer Sun Isn't the Vitamin D Fix We Think It Is
The sun can trigger vitamin D synthesis in the skin - but only under specific conditions that most Canadians, for most of the year, simply don't meet.
For UVB rays to stimulate vitamin D production, the sun needs to be at a high enough angle in the sky. In Canada, that window is narrower than most people realize. Even in summer, factors including cloud cover, air pollution, time of day, and the use of sunscreen - all of which are either common or recommended - significantly reduce UVB exposure.
Beyond geography and season, several individual factors affect how much vitamin D your skin actually produces from sun exposure:
Skin tone. Melanin, which gives skin its colour, absorbs UVB rays. People with darker skin tones require significantly longer sun exposure to produce the same amount of vitamin D as those with lighter skin - and the Newcastle study found their deficiency rates were among the highest, even in summer.
Age. The skin's capacity to synthesize vitamin D declines with age. Older adults produce less vitamin D from the same amount of sun exposure than younger people do - and they are also more likely to avoid direct sun or to cover up when outdoors.
Body composition. Vitamin D is fat-soluble, meaning it is stored in fat tissue. In people with higher body fat, vitamin D can become sequestered in fat cells and less available for circulation, which can suppress measured blood levels.
Where you live in Canada. The further north you are, the lower the sun's angle and the shorter the UVB window - even at the height of summer.
The Summer Supplement Mistake
One of the most common patterns we see: people who take vitamin D all winter, then stop in June because they assume they no longer need it.
Vitamin D levels that were already insufficient in winter don't recover quickly, and stopping supplementation during a period when sun exposure may not compensate means many people enter fall - and then cold and flu season - already depleted.
Research published in the journal Cells found that vitamin D plays a significant modulatory role in both the innate and adaptive immune response. Insufficient levels are associated with increased susceptibility to infection and with dysregulation of inflammatory pathways. This is not a minor consideration heading into respiratory virus season.
The practical takeaway: if you're stopping your vitamin D supplement because it's July, you may want to reconsider - particularly if you haven't tested your levels recently.
How to Actually Know Where Your Vitamin D Stands
The only way to know whether your vitamin D levels are adequate is to test them.
Blood tests measuring serum 25-hydroxyvitamin D (25(OH)D) give you your actual level — not an estimate based on how much time you think you're spending outside.
What the numbers mean (Canadian nmol/L):
- Below 50 nmol/L: Deficient
- 50–75 nmol/L: Insufficient
- Above 75 nmol/L: Sufficient for bone health
- 125 to <250 nmol/L: ImmunoCeutica's optimal target range - where research supports the strongest immune, bone, and overall health benefits
For a full breakdown of what your numbers mean, see ImmunoCeutica's guide to vitamin D levels in Canada.
Statistics Canada data (2024) indicates that approximately 32% of Canadians have insufficient vitamin D levels - and that figure is likely higher among older adults, people with darker skin tones, those who limit sun exposure, and those living at northern latitudes.
Testing removes the guesswork. It tells you whether you need to supplement, how much to take, and when to retest to confirm your levels have improved. The recommended window for retesting after starting or adjusting supplementation is 8–12 weeks.
What to Do This Summer
You don't need to avoid the sun - moderate, unprotected sun exposure during peak UVB hours can contribute to vitamin D production for many people. But it shouldn't be your only strategy, and it's not a reliable substitute for knowing your actual levels.
A sensible summer approach:
- Test your levels - especially if you've never tested, or if you stopped supplementing last spring
- Don't assume summer sun is enough - particularly if you're over 65, have darker skin, use sunscreen consistently, or live north of roughly the 45th parallel (which includes most of Canada's major cities)
- Continue or maintain supplementation based on your results and your healthcare provider's guidance
- Pair vitamin D with K2 - vitamin K2 works alongside vitamin D to help direct calcium appropriately and support cardiovascular and bone health
- Retest in fall - before heading into respiratory virus season, so you know where your levels stand
The Bottom Line
Summer feels like the safe season for vitamin D. The research - including this new June 2026 study from Newcastle University - suggests it isn't, for a meaningful proportion of the population.
The good news is that testing is simple, fast, and gives you the information you need to make a smart decision. You don't have to guess.
ImmunoCeutica's Vitamin D Test Kit lets you test from home with a simple finger-prick sample and receive your results with clear guidance on next steps.
Order Your Vitamin D Test Kit →
Sources: Newcastle University / European Journal of Clinical Nutrition (2026). "Study challenges a common belief about vitamin D and sunlight." ScienceDaily, June 24, 2026. Bikle D et al. (2023). Cells, 12(18), 2271. "Vitamin D and the Immune System." Statistics Canada. (2024). Vitamin D status of Canadians. McMaster University. (2025). "Here comes the sun: What you need to know about Vitamin D." McMaster News.