The primary purpose of this pilot study is to test a novel head worn light device (Re-Timer®) as an intervention to improve glucose metabolism in people with prediabetes. The hypothesis is that morning light treatment will improve glucose metabolism. This is a pilot study and the data from this project will be used to develop a larger clinical trial.

This is a pilot study to determine whether light treatment can improve glucose metabolism in people with prediabetes. Individuals will be asked to complete a baseline session with one-week of at-home sleep monitoring followed by a 24-hour stay in the clinical research unit. During this stay, we will sample saliva in the evening to measure melatonin to estimate the timing of the internal biological clock ("circadian phase") and then we will perform a 3-hour oral glucose tolerance test in the morning to estimate markers of glucose metabolism, including insulin sensitivity. The participants will then be given a light device and instructed on its use. They will use the device for four weeks and visit our laboratory every week for a check-in. At the end of the four weeks, they will repeat the 24-hour stay in the clinical research unit.

Inclusion Criteria: 34 subjects (50% female, age 40-65 y)

Subjects will be:

• Prediabetic (HbA1c 5.7% to <6.5%)
• overweight or obese (BMI>25 kg/m2)
• be free of moderate to severe obstructive sleep apnea (apnea-hypopnea index<30).

The laboratory sessions will occur during women's follicular phase or women will be postmenopausal (≥6 months since last menses).

Subjects will be scheduled to participate ≥ 1 month from travel outside the central time zone, and during a time with minimal special events.

Exclusion Criteria:

• Women who are pregnant, planning on becoming pregnant, or are breastfeeding.
• Women on oral contraceptives or hormone replacement therapy will be excluded (alters OGTT and melatonin).
• Men and women who have a child at home that does not sleep through the night will be excluded.
• Adults unable to consent, individuals who are not yet adults (infants, children, teenagers), pregnant women, and prisoners are also excluded.
• History of any form of diabetes, including use of diabetes medications
• Age outside 35-70 years (we will not enroll anyone older than 70 years because of a reduced response to light).
• Smokers
• Shift workers
• Failed urine drug test (drugs of abuse, nicotine)
• Eye disease/photosensitizing medications
• Sleep medications, diagnosed sleep disorders (history of treatment may affect glucose metabolism),
• Daily beta-blocker, NSAID or melatonin use (confounds DLMO)
• History of psychiatric disorders (confounds effect of light treatment, per relevant items from Mood Disorder, Psychotic Screening and Substance Use Disorders Modules of the Structured Clinical Interview for DSM-IV Axis I Disorders - Non-Patient Edition (SCID-IV/NP) to screen for schizophrenia, bipolar depression, substance abuse, suicidal ideation, obsessive compulsive disorder, PTSD), depressive symptoms using the Center for Epidemiologic Studies - Depression (CES-D) scale
• Irregular menses
• History of cardiovascular disease (excluding hypertension), endocrine, kidney, gastrointestinal or liver disorder, seizures, and cancer.

There were no participants enrolled into the dim light condition.

4 weeks

There were no participants enrolled in the dim light group and therefore there was no one at risk.

Our planned enrollment goal was 14 participants in each group and therefore we were underpowered in the bright light group to detect changes in all outcome measures. Further, we were not able to perform secondary analyses, which included between group comparisons.