Archaeologists have discovered a new way to find out if ancient people were getting enough sun: by checking their teeth. The New York Times reports that scientists have found a new marker for rickets, a childhood disease that can lead to bowed legs and hip deformities and results from deficiencies in vitamin D (which can be taken in by the diet or manufactured from exposure to the sun). It turns out that abnormalities in dentin, the hard substance that comprises the majority of a tooth, can reveal whether—and when—someone has had a bout of rickets. The deformities revealed themselves in slices of teeth like circles of bark in a tree—a year-by-year history of when a person was not getting enough vitamin D from the sun or food. The team says that in addition to lending insight into the history of rickets, the finding can better equip public health workers in addressing modern-day cases of the illness.