UNC-TV Science: How Much is Too Much?

UNC-TV Science: January 28, 2014
How Much is Too Much: Vitamin D May Cause Muscle Damage in Athletes

Vitamin D is easy to come by. You can get vitamin D2, which is made by plants, through a healthy diet. You can get extra vitamin D in the multivitamins and milk you find in any supermarket. And if you’re really in dire straits, you can stand in the sun for 10 minutes and your skin will make enough vitamin D3 to prevent a deficiency.

But new research from the Human Performance Lab at the N.C. Research Campus in Kannapolis shows that in large quantities, vitamin D may contribute to muscle damage in power athletes.

Vitamin D helps our bodies better absorb calcium, which is one reason why it is put in milk. Deficiencies in vitamin D cause weak bones and muscles, called rickets, in young people and osteomalacia in adults. David Nieman, who led the study said he originally thought that high levels of vitamin D2 would help athletes get more calcium into their muscles to better repair muscle damage.

Nieman and his colleagues studied two groups of NASCAR pit crews. They gave one group 3,800 international units (IU) of vitamin D2 harvested from mushrooms and the other a placebo. Both groups then trained as they normally would for the upcoming NASCAR season.

Instead of seeing healthier muscles, Nieman found that the group taking the vitamin D2 supplement had much more muscle damage than the placebo group. Nieman also found that the supplement group had less vitamin D3 (the stuff we make naturally) in their blood than the placebo group.

This is the first evidence that vitamin D2 may be harmful to the muscles of people who exercise heavily. One possible factor might be the dosage. According to the Mayo Clinic, osteomalacia patients take up to 2000 IU of vitamin D daily whereas the pit crew in the study took 3,800 IU. The Mayo Clinic does say, however, that people have taken up to 600,000 IU for muscle strength.

Since this finding is the first of its kind, it will need to be corroborated in further studies, but it does suggest that more vitamins are not always better vitamins. The study appears in the journal Nutrients.

- Daniel Lane

Daniel Lane covers science, medicine and the environment as a reporter/writer. He is currently pursuing a master's degree in medical and science journalism at UNC - Chapel Hill.