This study aims to enhance circadian signals to improve cardiometabolic functions in older adults though meal timing interventions and melatonin supplements. Cardiometabolic disease (CMD) is prevalent among older adults, but despite vigorous research to prevent it, it remains on of the greatest public health challenges. Previous research has shown that extended overnight fasting and melatonin supplements may enhance circadian signals which in turn would enhance cardiometabolic function in older adults.

This study will place subjects in one of four intervention groups, 1) Meal timing + Melatonin, 2) Meal timing + Placebo, 3) Melatonin, or 4) Placebo in order test out the effects of meal timing and melatonin both separately and together and cardio metabolic functions. The study will explore the effects of these interventions in acute-based setting and extended-based settings. This will allow us to test out the hypotheses of the study that meal timing can improve amplitude of circadian signals and improve cardiometabolic functions and sleep quality as well as melatonin improving cardiometabolic function and sleep quality. Finally, we will determine if the the addition of melatonin will further enhance the effects of the meal timing intervention for improving cardiometabolic function and sleep.

Inclusion Criteria:

• Older adults 55-75 years old.
• Females must be post-menopausal.
• BMI 25-45
• Regular eating schedule (consuming at least 2 meals/day) and sleeping schedules (deviation of ≤ 2 hours in daily mid-sleep time).
• Self-report sleep duration of ≥ 6.5 hours.
• Habitual mid-sleep time of 1-5 am.
• Habitual time in bed less than 9 hours
• HbA1c <6.5
• Habitual overnight fast of ≤ 13 hour (Determined by a mean overnight fast ≤ 13 hours over 3 days of self-monitoring of food intake)

Exclusion Criteria:

• History or current diagnosis of a primary sleep disorder (Chronic insomnia, restless leg syndrome, parasomnias, sleep apnea).
• AHI ≥30
• History of anemia.
• Diagnosis of diabetes or currently on any medications for diabetes.
• Endocrine dysfunction including PCOS.
• History of cognitive or other neurological disorders.
• History of DSM-V criteria for any major psychiatric disorder.
• Beck depression Index (BDI) of ≥16 indicating moderate depression.
• Mini mental status Exam <26 indicating cognitive impairment.
• Unstable or serious medical conditions.
• Individuals with pacemakers, defibrillators, mediation pumps, or any other implanted device.
• Any GI disease that requires dietary adjustment.
• Current or use within last month of melatonin.
• Current use of psychoactive, hypnotic, stimulants, or pain medications.
• Current use of hormone replacement therapy.
• Shift work or other self-imposed irregular sleep schedules.
• History of habitual smoking (≥6 cigarettes/week).
• Caffeine consumption >400 mg/day.
• Medically managed or self-reported weight loss program within past 6 months.
• Bariatric weight loss surgery.
• Blindness or visual impairment other than glasses.
• Allergic to heparin.
• Adults unable to consent will be excluded.
• Pregnant women will be excluded.
• Prisoners will be excluded.
• Individuals who are not yet adults (infants, children, teenagers) will be excluded.