Dentin, the material under the enamel that makes up the bulk of a tooth, forms in microscopic layers that compare to the rings of a tree. Adequate formation of those layers is dependent on Vitamin D. Dark streaks develop in periods when the body is deprived of the critical nutrient, usually because of a lack of sunlight.

The researchers, led by anthropologist Megan Brickley, had previously established that such microscopic defects remain in place and can be read later, in the same way a tree trunk can show years of good and poor growth. Because teeth do not decay as rapidly as flesh and bone, they can retain such information for hundreds of years post-mortem.

Combined with other data, Brickley says, patterns in dentin can create rich banks of knowledge about past conditions, including the health impacts of living in low-light environments.

"It's a living fossil of your life, starting in utero," Brickley says. "Conceivably, it would be possible to remove the molar of anyone and compare their health to the evidence in the tooth."

Early colonial settlers in Canada, for example, who were often wrapped head to toe, even in summer, commonly developed conditions such as rickets, or died prematurely from other conditions related to poor access to vitamin D.

Now the same team of researchers has established the value of such records, which begin during the original formation of teeth in the fetal stage, for reflecting the health of the mother during pregnancy. All of the body's primary or "baby" teeth, which start forming in utero, are lost in childhood.

The first permanent molars -- which emerge around age 6 -- also start forming in utero and stay in the mouth throughout one's adult life, where they retain a record of Vitamin D intake dating back to the mother's pregnancy.