Biological "Tree Rings" in Baby Teeth Reveal Critical Windows of Brain Vulnerability to Metals

Researchers at Mount Sinai use baby teeth "tree rings" to identify critical weeks in infancy where metal exposure impacts adolescent brain health and behavior.

By: AXL Media

Published: Apr 25, 2026, 4:25 AM EDT

Source: Information for this report was sourced from the Mount Sinai Health System and Science Advances.

A New Dimension in Environmental Chronology

The environmental medicine department at Mount Sinai has achieved a scientific first by combining dentition analysis with advanced neuroimaging to map the longitudinal impact of heavy metals. For years, the scientific community struggled to pinpoint exactly when the developing brain is most sensitive to environmental toxins, as blood tests only offer a snapshot of current exposure. By analyzing the layers of baby teeth, which form in utero and during infancy like tree rings, researchers reconstructed a weekly exposure history for 489 children in the PROGRESS cohort. This retrospective "hard drive" of the body allowed the team to link specific weeks of exposure to the structural and functional organization of the brain 12 years later.

Pinpointing the "Vulnerable Windows"

The study identified two distinct periods in early infancy that appear to be critical "turning points" for neurological development:

Weeks 4–8 after birth: A period of rapid early postnatal development where metal mixtures significantly impacted future behavioral stability.

Weeks 32–42 after birth: A late-infancy window that showed the strongest correlation with clinical-range behavioral symptoms, including anxiety, mood disorders, and attention deficits.