This study evaluates the effect of bright light on postprandial blood glucose metabolism in obese subjects with impaired fasting glucose and/or impaired glucose tolerance.

Light has a major influence on the biological clock and several studies suggest that bright light during the day and dim light in the evening are beneficial for the circadian timing system. Nowadays, large parts of the population spend 90% of their time indoors and are thereby exposed to artificial lighting instead of daylight. The artificial light levels are relatively low during the day and continue relatively late in the evening. The lack of a clear natural light-dark cycle could results in delayed timing of the biological clock relative to the behaviour. Optimizing the lighting conditions under controlled laboratory settings might lead to better alignment of the biological clock, which in turn could improve metabolic parameters such as glucose control.

Inclusion Criteria:

• Caucasian

• BMI 25-35 kg/m2

• Stable weight (+/- 3 kg in the last 3 months)

• One of the four criteria for prediabetes:

  • Impaired fasting glucose (6.1 mM to 6.9 mM)
  • Blood glucose values 7.8 - 11.1 mM 2h after glucose drink consumption during the oral glucose tolerance test (OGTT) in screening
  • Insulin Resistance: glucose clearance rate ≤ 360 ml/kg/min, as determined using the oral glucose insulin sensitivity (OGIS120) index
  • HbA1c of 5.7 - 6.4%.

Exclusion Criteria:

• Fasting plasma glucose ≥7.0 mM
• Blood donation one month prior to study and three months after finishing study.
• Participants with extreme chronotypes (going to bed extremely late/early).