- Aug 15, 2018
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With the days getting shorter and the sun hanging lower up here in Canada, a lot of us start wondering about vitamin D and whether low levels are quietly holding back our winter training. It's a fair question when you live above the 40th or 45th parallel and your skin isn't making much of anything from November through February.
The research on athletes and physically active people at higher latitudes is pretty consistent on status. A systematic review by Farrokhyar and colleagues in the journal Sports Medicine back in 2015 found that vitamin D inadequacy (under 80 nmol/L) was common in athletes living above 40° N, with the problem worse in winter and for indoor sports. More recent work, including a 2024 meta-analysis in Frontiers in Nutrition by Zhang and colleagues, confirms that daily vitamin D3 doses above 2000 IU for 4–12 weeks reliably push serum 25(OH)D from insufficient into the sufficient range, especially during winter at northern latitudes. That part is solid.
Where it gets more mixed is the performance side. The same Zhang meta-analysis found a significant boost in maximal quadriceps contraction strength after supplementation, but the overall effect across strength measures (vertical jump, 1-RM bench, handgrip) was small and not statistically clear. Earlier work by Farrokhyar in Sports Medicine in 2017 and a 2023 one-month trial in the Journal of the International Society of Sports Nutrition by Wang and colleagues also showed that raising 25(OH)D levels did not reliably improve handgrip, jump, or sprint performance once people were no longer frankly deficient. One longer Estonian study of young active men (Journal of the International Society of Sports Nutrition, 2022) kept levels from crashing over seven months of winter with 1200 IU but saw no handgrip difference versus controls.
So the picture that emerges is that keeping levels from tanking is easy and probably useful for bone and immune reasons, but the strength and power payoff for already-active lifters who are only moderately low seems modest at best. Most of the positive strength signals come from groups that started quite deficient or from specific muscle groups rather than global performance.
How are you handling winter vitamin D up here—bloodwork, a steady daily dose through the dark months, or just diet and whatever sun you can catch? And have you noticed any real difference in how your training feels or progresses once levels are in a better range?
The research on athletes and physically active people at higher latitudes is pretty consistent on status. A systematic review by Farrokhyar and colleagues in the journal Sports Medicine back in 2015 found that vitamin D inadequacy (under 80 nmol/L) was common in athletes living above 40° N, with the problem worse in winter and for indoor sports. More recent work, including a 2024 meta-analysis in Frontiers in Nutrition by Zhang and colleagues, confirms that daily vitamin D3 doses above 2000 IU for 4–12 weeks reliably push serum 25(OH)D from insufficient into the sufficient range, especially during winter at northern latitudes. That part is solid.
Where it gets more mixed is the performance side. The same Zhang meta-analysis found a significant boost in maximal quadriceps contraction strength after supplementation, but the overall effect across strength measures (vertical jump, 1-RM bench, handgrip) was small and not statistically clear. Earlier work by Farrokhyar in Sports Medicine in 2017 and a 2023 one-month trial in the Journal of the International Society of Sports Nutrition by Wang and colleagues also showed that raising 25(OH)D levels did not reliably improve handgrip, jump, or sprint performance once people were no longer frankly deficient. One longer Estonian study of young active men (Journal of the International Society of Sports Nutrition, 2022) kept levels from crashing over seven months of winter with 1200 IU but saw no handgrip difference versus controls.
So the picture that emerges is that keeping levels from tanking is easy and probably useful for bone and immune reasons, but the strength and power payoff for already-active lifters who are only moderately low seems modest at best. Most of the positive strength signals come from groups that started quite deficient or from specific muscle groups rather than global performance.
How are you handling winter vitamin D up here—bloodwork, a steady daily dose through the dark months, or just diet and whatever sun you can catch? And have you noticed any real difference in how your training feels or progresses once levels are in a better range?