Nutrition research (New York, N.Y.)Aug 13, 2026

Testing the separate and combined effects of early eating and daytime bright light therapy in adults with type 2 diabetes

Circadian Biology Weekly Brief ↗PubMed ↗DOI ↗

Updated Aug 14, 2026

Abstract

A total of 344 adults with type 2 diabetes will participate in a 16-week randomized controlled trial testing the effects of early time-restricted eating and daytime bright light therapy.

Disruption of circadian rhythms is associated with worsened glycemic control and cardiovascular health.
Optimizing circadian rhythms through earlier eating and bright light exposure may improve cardiometabolic health.
Participants will be assigned to one of four groups: control, early time-restricted eating, daytime bright light therapy, or both therapies combined.
The primary outcome of the trial is glycemic control, assessed through HbA1c and 24-hour glucose measurements.
Secondary outcomes include diurnal rhythms of melatonin and cortisol, as well as variations in glucose uptake throughout the day.
Tertiary outcomes will assess body mass, body composition, energy expenditure, cardiovascular risk factors, sleep quality, and psychological health.

Simplified

Disruption of circadian rhythms worsens glycemic control and cardiovascular health. Conversely, evidence suggests that optimizing circadian rhythms by eating earlier in the day, practicing intermittent fasting, and/or getting sufficient sunlight or bright light during the daytime improves cardiometabolic health. Here, we describe the protocol for a 2 × 2 randomized controlled trial testing whether two chronotherapies-early time-restricted eating (eTRE) and/or daytime bright light therapy (BLT)-can improve glycemic control, diurnal rhythms, and overall health in adults with type 2 diabetes (T2D). We will randomize 344 adults with insulin-independent T2D to 1 of 4 groups: (1) control, (2) eTRE, (3) daytime BLT, or (4) eTRE + daytime BLT. Participants in the eTRE groups will eat within an 8-hour window ending by 17:00, while those in the BLT group will receive bright light for 90 min/day before 15:00 and use blue-light-blocking glasses and blackout curtains at night. The intensive phase of the intervention is 16 weeks, with follow-up at the 1-year mark. The primary outcome is glycemic control as measured by HbA1c and 24-hour glucose, supplemented by additional assessments of glucose metabolism. Secondary outcomes are the diurnal melatonin and cortisol rhythms and the diurnal variation in glucose uptake. Tertiary outcomes include body mass, body composition, resting energy expenditure, cardiovascular risk factors, sleep parameters, quality of life, and psychological health. To our knowledge, this is the largest study to date of TRE in people with T2D and the largest study to test whether daytime bright light therapy can improve cardiometabolic health. Trial Registration: This trial was registered at clinicaltrials.gov (NCT04155619).

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Testing the separate and combined effects of early eating and daytime bright light therapy in adults with type 2 diabetes

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