Exposure to light may help Alzheimer's sufferers regain sleep-cycle rhythms and may reduce the need for institutional care.

Dutch and Japanese studies show that patients who received two hours of bright light therapy for a month registered improvements in sleep and in body temperature.

Alzheimer's disease is a progressive, degenerative disease that attacks the brain and results in impaired memory, thinking and behaviour.

Rhythm disturbances

People afflicted with Alzheimer's often suffer disturbances in circadian (daily) rhythm, which affects body functions such as sleep cycles, temperature, alertness and hormone production.

Impaired sleep and nocturnal restlessness place great burdens on the sufferer and the care giver.

Traditional sedatives have limited usefulness and are accompanied by side effects.

Eus Van Someren, of the Netherlands Institute for Brain Research in Amsterdam, said: "This is an important factor for home care and a major factor on whether people have to be institutionalised.

"Alzheimer's patients often receive very low light and receive little physical activity. Both of these are very important to our biological clocks."

Light bulbs

Some of the Alzheimer's patients studied were placed in front of bright light panels for two-hour periods, while others simply had brighter light bulbs placed in their living rooms.

Both groups showed improvement in their sleep patterns.

Researchers also tested low-level electrical pulse therapy, which helped stimulate circadian rhythm recovery.

Van Someren said outdoor sunlight and exercise also appeared to help restore circadian rhythms, although different patients may need the light therapy at different times of the day.