Dim Light Exposure or Melatonin Ingestion Lowers a Type 2 Diabetic's Blood Glucose Removal Rate: A Single Case

The purpose of this case study is to compare a Type 2 diabetic's postprandial glucoregulatory ability under two different room lighting conditions. The subject was a 56-year-old physically active male with well controlled blood glucose levels (HbA1c ≤ 6% for 5 y) from a combination of diet, exercise, and medication. Two hours post evening meal (380 kcal, 18 g fat, 44 g carbohydrate, 12 g protein), a 45 g carbohydrate challenge was given, and blood glucose was measured every 30 minutes for 2.5 hours under three conditions: dim light (<50 lux) (DL), bright light (>40000 lux) (BL), and bright light plus 6 mg melatonin (BLM). Each condition was repeated 3 times over a period of 6 months with each trial a minimum of seven days apart. The area under the average glucose concentration vs. time plot was different between the three conditions (BL = 909 ± 76; DL = 1078 ± 106; and BLM = 1130 ± 45 mmol·min·l^-1). Visual inspection of the average blood glucose vs. time plot suggested that DL and BLM displayed very similar patterns and magnitude, with both DL and BLM having the blood glucose concentrations at each time point that are noticeably greater than BL. Additionally, the average (± standard deviation) blood glucose concentrations for DL (8.8 ± 0.9 mmol·l^-1) and BLM (9.1 ± 1.1 mmol·l^-1) were respectively 18% and 22% greater than BL (7.5 ± 0.5 mmol·l^-1). Melatonin and/or dim light can reduce a Type 2 diabetic's glucoregulatory ability.