Lack of sleep can weaken the protective properties of regular physical activity in relation to cognitive functions in the elderly, according to a study conducted by scientists from University College London and published in the journal The Lancet Healthy Longevity. The study analyzed data from about nine thousand people aged 50 and older to find out how the interaction of sleep and physical activity can affect cognitive functions over time. Scientists found that people who were more physically active, but slept less than six hours a day, had a more rapid decline in cognitive abilities. In other words, after 10 years, their cognitive functions were inferior to the level of less active peers.