The growing popularity of exercise among middle aged men and women in India is backed up by the sheer numbers of people registering for running events in the country. Procam International, which is behind some of India’s most popular and biggest races, said the majority of their runners fall between 30 and 55 years of age. Although we may not know exactly why this is so, it isn’t surprising either.

There are plenty of benefits of exercise for everyone, including better physical health and a lower risk of death, disease and degenerative conditions. Regular physical activity can reduce the risk of dementia by up to 28%. All of this has been borne out by large scale scientific studies in recent times. Perhaps, as people grow older and the certainties of youth are stripped away, they become more aware of the need to take care of their bodies.

However, the one thing that could still remain neglected is getting enough sleep, especially with the nature of modern jobs. But to ignore sleep is to undermine the gains of fitness. When physical exercise is not complemented with proper sleep, many of the benefits of the exercise begin to fade away. Research has shown that sleep also plays its part in preserving brain health: Good quality sleep reduces the risk of dementia by 19%.    

A new study, titled Joint Associations Of Physical Activity And Sleep Duration With Cognitive Ageing: Longitudinal Analysis Of An English Cohort Study, published in the journal The Lancet Health Longevity earlier this month uncovers an important link between sleep, exercise and cognition. Researchers found that middle aged people who sleep less than six hours are less likely to benefit from exercise when it comes to healthy brain functions.

While previous studies have shown that regular exercise protects against age-related cognitive decline, the new paper finds that this protective effect of exercise wanes in middle aged people who don’t get enough sleep. The researchers observed 8,958 people aged over 50 for ten years and studied how various combinations of sleep and exercise habits affect cognition. They found that people who were more physically active but slept for less than six hours experienced faster cognitive decline.

Cognition is the basic functioning of the brain which includes decision-making, and the brain’s ability to think, read, learn, remember, reason and pay attention. Sleep is crucial because it recharges our brain and relaxes our mind. “In the case of sleep deprivation, this process of recharging slows down and the brain becomes inefficient which affects the normal functioning of the brain leading to memory loss, reduced attention span, poor decision-making capabilities and impacting the daily activities,” says Dr. Ashish Kumar Prakash, consultant for respiratory and sleep medicine at Medanta Hospital, Gurugram. The new study is important as it confirms that mere exercise is not enough to keep your brain sharp, sufficient sleep is equally important too. 

The finding that stands out is that shorter duration sleep is also associated with faster cognitive decline. “A sleep-deprived person faces difficulty in concentrating, focusing, paying attention and remembering. Such people tend to stay in a sleepy and drowsy state during the day (often referred to as brain fog) and may sleep at inappropriate times such as while studying, working or even driving, which could lead to accidents,” warns Prakash. 

There is also an immediate fallout of not getting enough shut eye. People with sleep deficiency experience a decreased ability to process new information, which impairs their ability to judge situations accurately and respond accordingly. It also takes a toll on one’s psychological wellbeing, affecting emotional and psychosocial interpretation of events and increasing stress levels. Studies show that inadequate sleep increases our tendency to select and remember negative memories. This, in turn, invariably affects our mood and feelings. 

On the physiological side, sleep is essential for the body to recover and heal muscles after exercise, as it provides the energy needed for physical activity, says Dr. Shama Kovale, an ENT consultant at the Kokilaben Dhirubhai Ambani Hospital in Mumbai. “Inadequate sleep can cause a lack of stamina and energy, making it difficult to exercise. Lack of sleep has negative effects on both physical and mental health. It raises the chances of developing health issues such as diabetes, high blood pressure, heart disease, and stroke,” she says. 

A common folk belief among people is that as we age, our sleep requirements go down, and that sleep problems start waking up as we advance in years. It is true that our sleep requirements are less compared to that of an infant, but no matter the age, everyone needs between 6-8 hours of good quality sleep each night, say doctors. 

As for the sleep problems and age links, Prakash dispels this myth saying, “Sleep problems do not have any relation with age. However, with increasing age, the levels of neuro-chemicals such as catecholamine, dopamine, serotonin and other substances in the brain decrease. Neurological diseases like Alzheimer’s and dementia, which are related with sleep disturbances, may manifest at an earlier age if a person is sleep deprived for a long time. Any person, irrespective of age, can suffer from problems related to cognition due to sleep deprivation.”  

Shrenik Avlani is a writer and editor and the co-author of The Shivfit Way, a book on functional fitness.