Microscopic markers of an infradian biorhythm in human juvenile ribs

Recent studies have indicated that there may be an infradian systemic biorhythm

that coordinates aspects of human hard tissue growth and influences adult body size. Here we

investigate if evidence of this biorhythm retained in human teeth as the periodicity of Retzius

lines (RP) corresponds with the microstructural growth of a non-weight bearing bone, the rib,

in a sample of 50 human juvenile skeletons. Using static histomorphometric methods, the RP

of one permanent tooth from each skeleton was calculated and combined with measures of

bone remodeling in a rib from the same individual. Results provide the first evidence that the

infradian biorhythm is linked to bone remodeling in children. Retzius periodicity was

negatively correlated with relative osteon area (r = -0.563, p = 0.008) and positively related to

Haversian canal area (r = 0.635, p = 0.002) and diameter (r = 0.671, p = 0.001) in children

between the age of 8 to 12 years. There was also a negative correlation between RP and the

relative cortical area of ribs (r = -0.500, p = 0.048). Relationships between bone remodeling

and the biorhythm were much more variable in younger children. Results imply that as the

biorhythm speeds up there is increased bone deposition during remodeling of the rib, leading

to the larger osteonal lamellar bone areas and smaller Haversian canals in children between 8

and 12 years of age. Our results support the idea that there is an infradian biorhythm that

coordinates aspects of human hard tissue growth.