Summary
Background
Evidence for a long-period biological rhythm present in the hard tissue of mammals is related to the average body mass of the species. Studies have only begun to investigate the role of this biorhythm in human physiology.
Methods
Biorhythm is calculated from naturally exfoliated primary molars for 61 adolescents. We determined whether time is related to longitudinal measurements of their weight, height, lower leg length, and body mass collected over 14 months between September 2019 and October 2020. We used univariate and multivariate statistical analyzes to isolate and identify relationships with biorhythm.
Results
Participants with a faster biorhythm typically weigh less each month and gain significantly less weight and mass over 14 months, compared to those with a slower biorhythm. Biorhythm is related to sex differences in weight gain.
Conclusions
We identify a previously unknown factor that is associated with the rapid change in body size that accompanies human adolescence. Our findings provide a foundation from which to explore new relationships between biorhythm and weight-related health risks.
Evidence of the biorhythm is captured in primary molars within 2 years of birth, as primary molar enamel forms. A faster biorhythm within 2 years after birth was related to lower weight and mass gains during early adolescence. A slower biorhythm is related to greater gains. Part of the Fig. (bottom panels) was created using a template from BioRender.com (2022).
Summary in plain language The human body undergoes cyclical changes such as the daily sleep-wake cycle and monthly menstruation. This study calculated a cycle that can be traced through the growth of children’s baby teeth. Cycle timing in different children was compared to changes in body size that occurred when these children were going through puberty. A link was seen between children’s cycle and the weight they gained over 14 months. Teens with a faster cycle generally weighed less each month and gained less weight over 14 months compared to those with a slower cycle. |
Comments
Research led by the University of Kent uncovered evidence of a biorhythm in human primary teeth that is associated with weight gain during adolescence.
An international research team led by Dr Patrick Mahoney at the Kent School of Anthropology and Conservation found that the biorhythm in primary "milk" molars (Retzius periodicity [RP]) is related to aspects of physical development during early adolescence. A faster dental biorhythm produced lower weight and mass gains.
RP is formed through a circadian-like process, occurring with a repetition interval that can be measured with a resolution of days. The rhythm relates to the period in which tooth enamel forms and is consistent within the permanent molars of individuals who do not retain evidence of developmental stress. Human modal RP has a cycle of almost seven days, but can vary from five to 12 days.
The first research of its kind published by Nature Communications Medicine found that adolescents with a faster biorhythm (five or six day cycle) weighed less, gained less weight and had the smallest change in their body mass index over a period of 14 period of one month compared to those with a slower biorhythm. Those with a slow biorhythm (seven or eight day cycle) produced the greatest weight gain.
Biological rhythm has been known to dental histologists for more than 100 years, but its importance for body mass and growth has recently emerged in studies comparing mammalian species. Research has now focused on the meaning of rhythm for humans.
A surprising finding was that participants with slower biorhythms were six times more likely to have a very high body mass index. Rapid change in body size is a natural consequence of adolescence, but excessive weight gain during puberty can have major health consequences, such as obesity in adulthood.
Dr Mahoney said: ’This research is an exciting first step. The next step is to determine whether the link we have discovered extends to adverse health outcomes in adults. “Potentially, baby teeth can have a record of this information many years before those results manifest themselves in adults.”
Dr Gina McFarlane, histologist on the project (also based in Kent), said: "Our findings provide a new avenue to explore the links between overweight children and adult health risks." Baby teeth naturally exfoliate (fall out) during the childhood years. "These discarded teeth contain precise information about a fundamental growth rate that we now know tracks adolescent weight gain."
The research article titled “Dental biorhythm is associated with adolescent weight gain” is published by Nature Communications Medicine. doi:10.1038/s43856-022-00164-x. This research project was funded by the Leverhulme Trust.
Final message
Our findings provide researchers with a new avenue to explore links between overweight and obese children and adult health risks, as well as an accelerated or slowed pace of maturation. Children’s naturally exfoliated primary (deciduous or "baby" teeth) may prove to be a novel marker of weight-related health risks and therefore be an actionable target for intervention many years before adverse health outcomes manifest in adulthood. The goal of developing a novel predictor of human weight and health is clearly worth pursuing.
To summarize, we calculated the timing of a biorhythm in primary molars and compared these values to the weight and mass gained by a cohort of adolescents over 14 months. Those with a faster 5- and 6-day biorhythm gained less weight and mass. Those with a slower 7- and 8-day biorhythm were more likely to have a BMI above the 95th percentile. These results provide the first evidence that a long-period biorhythm is associated with weight gain in adolescence. Our study points to a hypothalamus-mediated biorhythm that is active during a key period of human growth.
