Vitamin D: A Key To Endurance Sports Performance

Low Vitamin D levels are very likely limiting your running performance, and may compromise your health.

As runners, we want to do everything possible to perform well and have a great season. We are meticulous about our training schedules, hydration, sleeping habits, etc. Yet many times we fall short when it comes to nutrition.

My Story

In the summer of 2008, I started to feel rather lethargic during workouts and I struggled to maintain my normal training paces. My recovery from my harder efforts and long runs took longer than usual. I immediately and incorrectly assumed I had low serum ferritin levels indicating iron deficiency anemia.

One colleague to whom I lamented about my chronic fatigue asked me if I had checked my Vitamin D levels. “Vitamin D levels?” I exclaimed. I live in California, it is summer, and I am outside way more than the recommended 20 to 30 minutes a day. There is no way I could be Vitamin D deficient, especially since in addition to being exposed to sun most days, I eat a very balanced diet that includes a daily multivitamin supplement. However, a visit to my doctor confirmed that my serum 25–hydroxy-Vitamin D (25(OH)D) value was dangerously low (18 ng/ml). Normal levels are between 40-70 ng/ml. And for those with chronic diseases such as cancer, heart disease, diabetes, and multiple sclerosis, normal blood levels should be between 55-70 ng/ml. I was shocked.

I immediately started daily supplementation with 1,000 IU of vitamin D (Vitamin D3). After eight weeks, my 25 (OH)D level had improved somewhat (28 ng/ml). I did feel slightly better, but I wanted to recover completely, so I upped my dosage to 2,000 IU daily. A few weeks later my levels were within the normal range (56 ng/ml). I felt noticeably stronger and was able to hit my usual paces during training. And in October 2008, I set a half-marathon personal record.

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