The circadian system is strongly linked to type 2 diabetes. Adults with type 2 diabetes have circadian rhythms that are both weakened and mistimed. Weak rhythms may be due to insufficient bright light exposure during the daytime, irregular meal timing, or grazing on food throughout the day. Mistiming may be due to ill-timed food intake or light exposure-such as eating later in the day or light exposure at night-which causes central and peripheral circadian clocks within the body to become out of sync (circadian misalignment). This circadian misalignment impairs glucose metabolism: data now show that eating late in the day and light exposure at night rapidly elevate glucose (blood sugar) and insulin levels in humans within days. Conversely, well-timed food intake and light exposure appear to improve glycemic (blood sugar) control, circadian rhythms, and several other aspects of health.~This study will test the health effects of eating early in the daytime (early time-restricted feeding; early TRF) and timed light therapy in adults with type 2 diabetes. The study will test the following aims:~Determine whether early TRF and/or timed light therapy improve glycemic control~(a) Determine how early TRF and/or timed light therapy affect the central and peripheral circadian clocks and (b) determine which patients benefit the most from circadian-based therapies~Determine whether early TRF and/or timed light therapy improve sleep, body weight, body composition, cardiovascular risk factors, quality of life, and psychological health.~Approximately 344 veterans and civilians aged 30-80 with insulin-independent type 2 diabetes will be randomized to the following 2 x 2 study design:~No change in eating or light exposure habits~Early TRF~Timed light therapy~Early TRF and timed light therapy~Participants will be asked to follow their assigned treatment for 16 weeks and then be followed up for an additional eight months (1 year in total). Baseline and post-intervention testing will be conducted during a 38-hour inpatient (hospital) stay. Testing will involve three 3-hour meal tolerance tests to determine insulin sensitivity and secretion; 24-hour measurement of glucose, insulin, and C-peptide levels; 24-hour measurement of cortisol and melatonin to measure the phase and amplitude of the central clock; and a constant glucose infusion to determine the phase and amplitude of the effective glycemic (peripheral) circadian clock. Sleep, weight loss, body composition, and cardiovascular risk factors will also be measured, and questionnaires and an interview will be administered to determine improvements in quality of life and psychological health.~Note: Pre-registered primary and secondary outcomes are listed below. Pre-registered tertiary outcomes appear in the study protocol, which will be uploaded to this website.
The purpose of this study is to test whether eating earlier in the day and/or timed light therapy can improve blood sugar in people with type 2 diabetes. This study will also test whether these treatments improve other aspects of health, including the circadian (biological) clock, sleep, weight, body composition, cardiovascular health, quality of life, and mood.