Summary: Rising carbon dioxide in the atmosphere may be leaving a measurable imprint inside the human body. Researchers analyzing more than two decades of U.S. health data found that blood bicarbonate levels have climbed about 7% since 1999, while calcium and phosphorus have declined—changes that closely track increasing atmospheric CO2.

I guess it makes sense - the more CO2 you breath, the more your body has to deal with, and it's physiologically relevant.