by Sarah Voelkel Feierstein PT, DPT, OCS, CMPT

Vitamin D is an important nutrient for athletes, specifically runners. Vitamin D comes from food, supplements, and sun exposure and is converted by the liver and kidneys into its active form which helps regulate calcium and promote bone mineralization. In addition, it plays a role in cell growth and neuromuscular and immune function. Deficiency is linked to muscle myopathy, muscle weakness, and muscle fatigue. Athletes are recommended to have blood levels of vitamin D above 50 ng/mL.

Continuous eccentric exercise (eg. downhill running) is known to cause muscle damage. A previous study shows the prevalence of vitamin D deficiency in extreme endurance athletes has a delayed physical performance. Optimal Vitamin D dosage for athletic performance and recovery is controversial.

The authors in the article, The Effect of Vitamin D Supplementation on Serum Total 25 (OH) Levels and Biochemical Markers of Skeletal Muscles in Runners, created a double-blind placebo-controlled clinical trial to observe the effects of a daily vitamin D supplement on blood levels of 25 (OH)D and biomarkers for muscle damage following an eccentric run. Vitamin D is transported by way of 25 (OH)D in the blood, making it a good indicator for levels of this vitamin present at a given time. They also looked at skeletal muscle biomarkers, proinflammatory cytokines, and tumor necrosis factor alpha levels which all cause inflammation and are linked to muscular pain in the process of muscle recovery.

Twenty-four male ultramarathon runners with seven years-experience were randomly assigned to either a three-week placebo (control group) or a 2000 IU vitamin D supplementation protocol (the experimental group). The subjects followed controlled diets void of caffeine, supplements, or alcohol for three weeks prior to the start of the study and three weeks during the study.

The runners participated in an eccentric downhill treadmill running test at 70% of their VO2 Max before and after the vitamin D or placebo intervention. Venous blood draws were taken at rest, immediately after the exercise, and at one hour and 24 hours post-exercise.

There was a significant effect of vitamin D supplementation on blood concentrations at baseline between pre and post intervention in the experimental group. There was a higher post intervention vitamin D serum levels in the experimental group. There were decreased skeletal muscle biomarkers including troponin, creatine kinase, and TNF-alpha level at one-hour post-exercise in the supplement group. At the 24-hour mark, there was significantly lower creatine kinase activity in the supplemental group. There was a negative correlation between post exercise vitamin D levels and skeletal muscle biomarker levels in the supplemental group.

The goal of the study was to see if there was a relationship between vitamin D supplementation, blood serum 25(OH)D levels, and skeletal muscle biomarkers to amplify recovery in marathon runners. The results show that vitamin D supplementation did, in fact, decrease the amount of muscle inflammatory cells at 1 hour and 24 hours post running. Strenuous exercise with eccentric muscle contractions may be attributed to muscle fatigue due to muscle membrane damage. With less muscle damage, there is a decreased recovery time.

Three weeks of vitamin D supplementation had a positive effect on serum 25(OH)D levels in endurance trained runners and a marked decrease in post-exercise biomarker levels. Vitamin D supplementation might play an important role in the improvement of muscle function and prevention of skeletal muscle injuries following exercise with eccentric muscle contraction in athletes.

We treat many runners at Physical Therapy First. This study shows that Vitamin D is important in decreasing pain and improving the recovery time after long distance running. In addition to a proper physical therapy training program to decrease your risk of sustaining a running-related injury, we recommend talking with your physician about vitamin D levels and possibly supplementing at a recommended dosage in order to promote improved muscle recovery after your next training run or race.

Zebrowska, A., Sadowska-Krepa, E., Stanula, A., Waskiewicz, Z., Takomy, O., Bezuglov, E., Nikolaidia, P… Knechtle, B (2020). The Effect of Vitamin D Supplementation on Serum Total 25 (OH) Levels and Biochemical Markers of Skeletal Muscles in Runners. Journal of International Society of Sports Nutrition. 17:18