Reduced blue light transmission to the retina, which results from aging and yellowing of the lens, strongly correlates with sleep disturbance, a recent Danish study suggests. Results revealed that every 1% increase in blue light lens transmission reduced the odds of sleep disturbance by 5%. Those odds also increased significantly with the extent of autofluorescence, a measure of lens transmission and yellowing.

Line Kessel, M.D., Ph.D., and co-authors illustrated the odds ratios using a clinical example. A 50-year-old, nonsmoking, non-diabetic woman with a low risk of ischemic heart disease in the 97.5% upper-normal range of blue light lens transmission had a 16.4% risk of sleep disturbances. In contrast, a 50-year-old woman with a similar profile who was in the 2.5% lower-normal range of blue light lens transmission had a 37.9% risk of sleep disturbances.

Sleep patterns and circadian rhythms are regulated through the retinohypothalamic tract in response to stimulation of the retinal ganglions––primarily by blue light. The authors hypothesize that lens yellowing might act as a filter for blue light in older people, which could explain why they are more prone to sleep disturbance. It’s possible that the aging process of the lens is a primary contributing factor to sleep disorders. 

“Our results support that choosing the right indoor lighting conditions may have a beneficial effect on sleep and that blue light therapy might be used to modulate circadian sleep disorders,” the authors noted.

Kessel L, Siganos G, Jørgensen T, Larsen M. Sleep disturbances are related to decreased transmission of blue light to the retina caused by lens yellowing. Sleep. 2011 Sep 1;34(9):1215-9.