Human adipose tissue expresses intrinsic circadian rhythm in insulin sensitivity.
Level 5 - mechanism / opinion, no new human data
Ex vivo laboratory study on human adipose tissue biopsies
PubMed 27256623 · doi:10.1096/fj.201600269RR
What was done
Researchers evaluated whether human fat tissue exhibits cell-autonomous 24-hour rhythms in insulin sensitivity. Subcutaneous and visceral adipose tissue biopsies were collected from severely obese patients (mean body mass index 41.8 ± 6.3 kg/m²; mean age 46 ± 11 years) during gastric-bypass surgery. Tissue explants were cultured in vitro and stimulated with varying insulin concentrations (0, 1, 10, and 100 nM) every 4 hours over a 24-hour cycle to assess insulin signaling via AKT phosphorylation. Rhythms were also correlated with participants' habitual sleep timing and duration.
What was found
Subcutaneous adipose tissue displayed a significant circadian rhythm in insulin signaling (P < 0.00001), reaching peak sensitivity (acrophase) around noon, which was 54% higher than at midnight (P = 0.009). The amplitude of this rhythm correlated positively with sleep duration (r = 0.53, P = 0.023) and negatively with bedtime (r = -0.54, P = 0.020). In contrast, visceral adipose tissue showed no detectable circadian rhythm in insulin sensitivity (P = 0.643).
Why it matters
The findings demonstrate an intrinsic peripheral clock mechanism in subcutaneous fat that may partly explain why whole-body insulin sensitivity fluctuates across the day, independent of central feeding cycles.
Limits
The abstract does not report the total participant sample size (n). Biopsies were obtained exclusively from middle-aged individuals with severe obesity undergoing bariatric surgery, limiting generalizability to lean or healthy populations. Findings reflect ex vivo tissue culture conditions and do not directly measure in vivo whole-body metabolic flux.
Cited by
- supports Human insulin resistance reaches its highest levels around 10:00 PM due to circadian regulation.