Until recently doctors believed that the hemoglobin in our red blood cells carried only oxygen and carbon dioxide when we are in good health.

However, according to an article published in the April 2015 issue of the Proceedings of the National Academy of Sciences, hemoglobin also carries a molecule called nitric oxide (NO).

It turns out that NO is essential in dilating blood vessels where oxygen is released in order to maximize its delivery to the tissues that need it.