Climatological Effects on Bone Growth

Objective: We aim to measure lamellar growth rate variability for known calendrical time and environmental location and identify the influence of climate on bone growth.  Bone is an incremental tissue, providing the means to interpret vertebrate life history events. One bone lamella corresponds to a long period rhythm in enamel, the striae of Retzius; the number of daily enamel increments formed between adjacent striae is the repeat interval (RI). Given that lamellae represent a discrete period, variability in their widths denotes variability in growth rate.

Methods: Human dental and skeletal specimens from individuals of known life history were acquired from the University of Malawi College of Medicine (UMCOM). Tooth and midshaft femur/humerus histological sections were prepared and analyzed for RI and lamellar bone widths respectively.  Regional climate data were acquired from the Meteorolgical Services of Malawi.  Graphical analyses of rainfall data were compared with graphical representations of lamellar bone growth variability of the individuals in approximate alignment with real years.

Results: Using formal techniques for measuring lamellar widths from images of anisotropic bone lamellae, we describe bone growth rate variability with near-weekly resolution. We observe a number of moderately long term rhythms corresponding to ca. 6-8 weeks and longer term rhythms corresponding to annual cycles.  In addition, growth rate variability was observed to coincide with dramatic changes in climate.

Conclusion: We observe periodic growth rate variability in human bone, including variability on annual cycles and that corresponding to the 1979-1982 period of drought in Malawi, revealing an interaction between climate variability and socioeconomic status.