One of the possible causes of disturbed circadian rhythms and sleep in the elderly may be impaired photic input to the circadian clock. Age-related changes in lens density are known to reduce the transmission of short wavelength light, which has been shown to be most effective in suppressing nocturnal melatonin. The aim of the study therefore was to investigate age-related changes in melatonin suppression in response to short and medium wavelength light. Young premenopausal (n=13) and postmenopausal (n=21) women were exposed to 30 min of monochromatic light at two different wavelengths and irradiances (lambda(max) 456 nm: 3.8 and 9.8 microW/cm(2); lambda(max) 548 nm: 28 and 62 microW/cm(2)). Melatonin suppression was compared across light treatments and between age groups. Significantly reduced melatonin suppression was noted in the elderly subjects following exposure to short wavelength (456 nm) light compared to the young subjects. These results are likely to reflect age-related changes in lens density.