How natural daily melatonin and body temperature patterns relate to morning or evening activity preferences in young and older people

Among 68 young and 40 older subjects, older morning types exhibited an earlier circadian phase and a shorter phase-wake time interval compared to younger morning types.

• Younger morning types woke at a later circadian phase despite waking at an earlier clock hour than evening types.
• Older morning types had a shorter interval between circadian phase and usual wake time compared to younger morning types.
• Age-related changes in phase angle are not fully explained by a shift toward morningness.
• Younger evening types exhibited a phase-wake time interval more similar to older morning types.

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