Synchrony between 24 hour solar cycle and internal biological rhythms is important for our physiology.The retinal ganglion cells, ipRGC, are photosensitive .Light activate the pigment melanopsin and these project the light information to the SCN (Supra Chiasmatic Nucleus) in hypothalamus ( SCN is the biological/molecular clock).SCN projects to paraventricular nucleus of the hypothalamus (PVN) and to the thalamus. The retinal cells and SCN are projecting to prefrontal cortex, amygdala and hippocampus and this may have direct effects on mood.
Exposure to ” round the clock” light is universal now and this could be creating a chronic disruption of the above synchrony . Could this be contributing to depression?
TA Bedrosian and RJ Nelson review the evidence for this hypothesis.
There is more depression among shift workers. Light at night (LAN) could be one factor contributing to this. Circadian disturbances are also common in depression. Pineal melatonin secretion is also disrupted by LAN and accumulating evidence suggests that melatonin is related to mood. Studies hitherto haven’t produced direct data linking LAN and depression.
Animal studies suggest that LAN influences mood directly, without disrupting circadian rhythms. A similar link in humans remains to be demonstrated.
Light at night (LAN) is a norm now. Even if it has deleterious effects, we wont be able to prevent LAN. Replacing standard bulbs with red ones where possible, or using glasses that only transmit red wavelengths, may prevent the disruptive effects of LAN.
Epidemiological studies have identified the relationship between LAN and breast cancer. Authors hope that similar interest and research would throw light here as well.
Summary of the article:
Bedrosian TA, Nelson RJ. Mol Psychiatry. 2013 Jul;18(7):751-7.