Human circadian clock genes (CCG) are expressed in tissues throughout the body, including the hair report Makoto Akashi and his colleagues, Yamaguchi University, Japan.

They have found that RNA from hair follicles displays CCG peaks of activity in step with daily routine. If the sleep-wake cycle is disturbed, these peaks are also disturbed. After three weeks of waking progressively later, subject’s gene expression no longer correlated with their lifestyle.

There was a similar lag in shift workers on a three week rotation. Clock gene activity lagged five hours behind the workers’ lifestyles indicating three weeks was not long enough for the body clock to adapt to the new schedules.

Because these genes control everything from organ function to eating cycles, using hair to measure the time-lag in a noninvasive way could help explain some of the health problems shift workers develop.

• Noninvasive method for assessing the human circadian clock using hair follicle cells
  M. Akashi, H. Soma, T. Yamamoto, A. Tsugitomi, S. Yamashita, T. Yamamoto, E. Nishida, A. Yasuda, J. K. Liao, K. Node,
  Proc. Nat. Acad. Sci. 2010, 107.
  DOI: 10.1073/pnas.1003878107