Although vitamin D deficiency is linked to muscle weakness and pain, supplements of vitamin D2 increase muscle soreness and recovery time after bouts of intense exercise. The research was conducted on NASCAR pit crews, who train hard so they can move really fast and lift heavy objects easily during a pit stop. The 28 crew members were interested in being research subjects because they are always striving for an extra edge.
Half of the volunteers were randomly assigned to take capsules of portobello mushrooms that had been exposed to ultraviolet light so they would produce vitamin D2. The other half got placebo capsules. During the six week wintertime study, blood samples were taken and exercise sessions were monitored.
Surprisingly, the scientists found that vitamin D3 levels dropped in the participants taking vitamin D2 (3,800 IU daily). They also suffered more from muscle damage. This was unexpected because prior to this study there had been no indication that vitamin D2 might affect levels of vitamin D3, the vitamin humans make in their skin when exposed to sunlight.
The results of this study may have implications for the common practice of prescribing 50,000 IU weekly of vitamin D2 to treat vitamin D deficiency. Although this seems to work for some people, others have complained about side effects. SJ wrote:
“I experienced very severe acid reflux around the time I did a 50,000 IU/week vitamin D regimen. It was not until much later that I started to wonder if the two things were linked. I looked for information online to see if there was any case for that suspicion but found nothing. After doing a second vitamin D regimen about a year later, the reflux flared up again, though not as severely. I became even more suspicious of a connection. Now, months after finishing the second regimen, I try to keep my D levels up by taking 5000 IU of D3 once a week. I find that I often have mild to moderate heartburn on the day that I take the pill. I am glad to see some evidence that this may be recognized as an actual side effect.”
