circadian

Introduction

In reference to biologic rhythms with a cycle of about 24 hours.

Pathology

• evening chronotype (a circadian preference to go to sleep late at night) may be associated with an unhealthy lifestyle & increased risk of type-2 diabetes
• disrupted circadian rhythms in cognitively normal adults linked to higher subsequent amyloid-beta PET burden
  • link stronger in APOE4 carriers

Genetics

• human myocardium biopsy samples found that time of day affected expression of nearly 300 genes

Pharmacology

• > 50% of the 100 best-selling drugs in the U.S. target products of genes with circadian periodicity

Physiology

• the suprachiasmatic nucleus acts as the central pacemaker for the human circadian system
• when the retina processes wavelengths of light typically emitted by the sun, a series of signal transduction eventactivate expression of circadian genes within the suprachiasmatic nucleus
• liver, muscles, fat tissue, beta cells, & the gut may have circadian clocks of their own
  • timing of food may synchronize may synchronize these peripheral circadian clocks
  • glucose metabolism is tied to a circadian rhythm & influenced by food timing
  • healthy individuals process sugar from nighttime meals more slowly than they process comparable morning meals
  • when peripheral circadian oscillators are not in sync withthe central oscillator, deranged metabolism occurs with weight gain & development of glucose intolerance
  • restricted eating to a period of 10-12 hours each day has benefits in glycemic control & weight reduction

Comparative biology

• 43% of protein-coding genes in mice show circadian variation

Notes

• mobile smartphone application that helps patients understand their body's rhythms while contributing to research
• Nobel Prize in Physiology or Medicine 2017 for work on the molecular mechanisms of circadian rhythm

More general terms

• periodicity

Additional terms

• chronotype; night owl; early bird
• circadian clock oscillator