Ageing eyes,not lifestyle,to blame for health woes

Now a body of research supports a largely unrecognised culprit: the ageing of the eye

For decades,scientists have looked for explanations as to why certain conditions occur with age,among them memory loss,slower reaction time,insomnia and even depression. They have scrupulously investigated such suspects as high cholesterol,obesity,heart disease and an inactive lifestyle.

Now a body of research supports a largely unrecognised culprit: the ageing of the eye. The gradual yellowing of the lens and the narrowing of the pupil that occur with age disturb the bodys circadian rhythm,contributing to a range of health problems,these studies suggest. As the eyes age,less and less sunlight gets through the lens to reach key cells in the retina that regulate the bodys circadian rhythm,its internal clock.

We believe the effect is huge and that its just beginning to be recognised as a problem, said Dr Patricia Turner,an ophthalmologist in Leawood,Kansas,who with her husband,Dr Martin Mainster,a professor of ophthalmology at the University of Kansas,has written extensively about the effects of the ageing eye on health.

Circadian rhythms are the cyclical hormonal and physiological processes that rally the body in the morning to tackle the days demands and slow it down at night. This internal clock relies on light to function properly,and studies have found that people whose circadian rhythms are out of sync,like shift workers,are at greater risk for a number of ailments,including insomnia,heart disease and cancer.

So-called photoreceptive cells in the retina absorb sunlight and transmit messages to a part of the brain called the suprachiasmatic nucleus,which governs the internal clock. The SCN adjusts the body to the environment by initiating the release of melatonin in the evening and cortisol in the morning. Melatonin is thought to have many health-promoting functions,and studies have shown that people with low melatonin secretion have a higher incidence of many illnesses.

Dr Mainster and Dr Turner estimated that by age 45,the photoreceptors of the average adult receive 50 per cent of the light needed to fully stimulate the circadian system. By age 55,it dips to 37 per cent,and by age 75,to a mere 17 per cent. Because of these changes,Dr Mainster and Dr Turner believe that with age,people should make an effort to expose themselves to bright sunlight or bright indoor lighting when they cannot get outdoors. Older adults are at particular risk,because they spend more time indoors.