Metabolic effects of morning light

Type 2 diabetes is a major threat to human health. Interestingly, the incidence
of obesity and type 2 diabetes correlates to the presence of artificial light.
Light for the non-visual system is detected in the retina by specialised
intrinsically photosensitive retinal ganglion cells (ipRGCs) that communicate
directly to various hypothalamic areas, and thereby modulate hormonal secretion
and autonomic activity. Light has time dependent autonomic effects in humans,
and administration of a light pulse to rats directly alters metabolic gene
expression in the liver. In this pilot study, we aim to determine if light
directly influences human glucose metabolism. We hypothesize that morning
bright light exposure decreases postprandial glucose excursions.

To determine the direct effects of morning light intensity on postprandial
glucose and lipid metabolism and metabolic gene expression in adipose tissue.

cross-over intervention study

Subjects enter the facility in the evening. They will remain in normal room
light (100-200 lux) for 4 hours. They receive a standard meal 2 hrs before
bedtime. They sleep for 8 hrs in the dark (1 lux). From wake-up time, they will
be subjected to either bright light (4000 lux) emitted by EnergyLights
((Philips Consumer Lifestyle B.V., Drachten) or dim light (10 lux). 1,5 hr
after lights on subjects will consume a standard 600 kcal liquid meal
(EnsurePlus). Blood samples will be obtained at regular intervals until 240 min
after the meal. Resting energy expenditure (REE) wille be performed 3.5 hrs
after breakfast. An adipose tissue biopsy will be obtained 4 hrs after the
meal.

Total study duration is three weeks. Participants will visit the Academic
Medical Center five times: three short visits (<1hr) and two 14hr admissions.
At study entry, patients will undergo physical examination and one blood sample
will be obtained. Participants will record sleep-wake times in a diary for five
days. Prior to each admission they will wear an actiwatch to verify adherence
to a stable sleep-wake rhythm. During each admission, participants will sleep
for one night at 1 lux in the experimental room. They will remain undisturbed
during this night. In the morning blood samples will be obtained from an
indwelling canula in a peripheral arm vein. Total amount of blood obtained
during the study will be 210 ml (100 ml at each admission and 10 ml at study
entry). Subcutaneous fat biopsies from the periumbilical region will cause
minor discomfort and a subcutaneous hematoma that will resolve over time.
Subcutaneous adipose tissue biopsies have negligible risks of infection or
haemorrhage. Use of EnergyLights may cause minor temporal complaints such as
headache or tired eyes. The 400 ml (600 kcal) Ensure Plus breakfast may for
some people be above the average breakfast size. This may cause a transient
sense of fullness.
Patients will receive a financial compensation of 200 euros and travel
expenses.