Table 1.

Evaluation of the circadian rhythm in various conditions and disorders using human hair follicles.

Conditions/Disorders	Participants (Number)	Tissue/Cells & Collection Method	Observations		Reference
			Circadian Markers	Results
Day and night shifts	Female diurnal workers (10) and shift workers (10)	Keratinocytes and dermal papilla stem cells isolated from HFs	PER1 BMAL1	Protein expression increased in the deregulated group	[68]
	Rotating shift workers (6)	Scalp HFs; 3 h intervals	PER2 PER3 NR1D1 NR1D2	Phase: ~2 h delay	[12]
	Male daytime workers (11), nurses and doctors (10), and factory workers (11)	Beard HFs; 4 h intervals	PER3	Mesor: decrease after consecutive night shifts Amplitude: fewer workers with significant 24 h rhythms after night shifts Phase: n.s.	[69]
			NR1D1	Mesor: n.s. Amplitude: n.s. Phase: n.s.
			NR1D2	Mesor: decrease after one night shift Amplitude: fewer workers with significant 24 h rhythms after night shifts Phase: n.s.
	Female shift (23) and daytime nurses (25)	Pubic HFs; Five time points	PER2	Shift nurses exhibited lower circadian variations than did daytime nurses	[70]
Sleep disorders	Healthy male participants (16) and male patients with the delayed sleep–wake phase disorder (18)	Beard HFs; 4 h intervals	PER3	Amplitude: n.s. Phase: delayed in the group with delayed sleep-wake phase disorder	[71]
			NR1D1	Amplitude: n.s. Phase: n.s.
			NR1D2	Amplitude: n.s. Phase: n.s.
	Latent circadian rhythm sleep–wake disorders (24)	Scalp HFs; 8 h intervals	PER3	Peak time of PER3 expression and GUw are positively correlated	[72]
Physical activity	Adult males (20)	Facial HFs; 4 h intervals	PER3	Amplitude: higher in the active group	[73]
			NR1D1	Amplitude: n.s.
			NR1D2	Amplitude: n.s.
	Healthy male (1)	Facial HFs; 4 h intervals	PER3 NR1D1 NR1D2	Mesor: n.s. Amplitude: n.s. Phase: 2–4 h delay during habitual nighttime training	[74]
Chronotype	Young men (24)	Facial HFs; 4 h intervals	PER3 NR1D1 NR1D2	Peak time of PER3 expression was delayed in the eveningness group; change in the peak time of NR1D1 and PER3 expression from the Friday to Monday trial was high in the eveningness group	[75]
Decision-making	Extreme morning (16) and evening chronotype (8)	Plucked hairs; 8 h intervals	PER3 NR1D2	3 h phase differences between morning and evening chronotypes	[76]
Energy metabolism	Total parenteral nutrition (TPN) (78) and non-TPN aged subjects (6)	Scalp HFs; 6 h intervals	PER3	Peak time of PER3 relative to wake-up time was delayed in TPN patients	[77]
Age-related diseases	Nondementia elderly subjects (10) and old–old dementia patients (5)	Scalp HFs; 6 h intervals	PER3 NR1D1 NR1D2	Peripheral circadian phases in dementia subjects were within normal range	[78]
	Parkinson’s disease patients (17)	Scalp HFs; 6 h intervals	PER3 NR1D1 NR1D2	Phase: delayed after bright light therapy	[79]

Abbreviations: HFs—hair follicles; n.s.—nonsignificant; GUw—local time of getting out of bed on working or school days. Gene names are italicized and protein names are not.