The Science of the Afternoon Nap

In many parts of the world, a short sleep after lunch is an accepted part of daily life. Shops close, streets fall quiet and families rest through the hottest hours of the day. In Britain, by contrast, napping has often been associated with laziness, old age or illness, and an employee found asleep at their desk would be unlikely to receive much sympathy. Over the past few decades, however, sleep researchers have begun to argue that the afternoon nap deserves to be taken far more seriously.

Part of the explanation lies in the body's internal clock. Most adults experience a natural dip in alertness in the early afternoon, usually between one and three o'clock. Many people blame this on a heavy lunch, but studies show that the dip occurs even in people who have eaten nothing, which suggests it is built into our biology. Dr Helena Marsh, who runs a sleep laboratory attached to a large hospital, believes that humans may originally have been designed to sleep twice a day, once at night and again briefly in the afternoon.

Historians have found evidence that napping was once more widespread in Britain too. Before electric lighting, many people went to bed soon after dark and woke for a period in the middle of the night, and short daytime rests were common among farm workers during the long days of harvest. The habit declined as factory work, fixed hours and long journeys to work made it impractical. Today, a British adult who wants a nap may struggle to find the time or a suitable place, and many feel guilty about taking one.

The benefits of a short nap are well documented. In laboratory tests, volunteers who slept for twenty minutes after lunch performed better on tasks requiring attention and reaction speed than those who stayed awake. Naps also appear to help the brain store new information: in one experiment, people who learnt a list of words and then napped remembered more of them later than people who had spent the same time watching a film. Some studies have also linked regular napping with improved mood, although Marsh admits that this evidence is less conclusive.

Timing and length, however, make a considerable difference. A nap of between ten and thirty minutes generally leaves people feeling refreshed. Sleep for much longer than this, and the brain is likely to enter deep sleep, from which waking is difficult and unpleasant. This state, known as sleep inertia, can cause grogginess for up to half an hour and may temporarily make performance worse rather than better. Napping late in the afternoon can also make it harder to fall asleep at night, which is why Marsh advises people with insomnia to avoid daytime sleep altogether.

Some employers have started to take notice. A number of technology firms and call centres now provide quiet rooms where staff can rest during breaks, and long-distance drivers are routinely advised to stop and sleep for a short period if they feel drowsy. Hospitals have also experimented with allowing nurses and doctors on night shifts to take brief, planned naps, after research suggested that this reduced errors in the early hours of the morning. Supporters argue that such policies cost little and can improve both safety and productivity.

Not everyone is convinced. Some managers worry that rest rooms will be misused, or that staff who nap will appear unprofessional to customers. There are also questions about whether the findings from laboratories apply in noisy, busy workplaces, where it may be hard to fall asleep quickly. And several large studies have found that older people who nap for long periods each day are more likely to suffer from certain health conditions, although researchers stress that the napping may be a sign of an existing illness rather than its cause.

For Marsh, the key message is that napping is neither a cure-all nor a sign of weakness. A short sleep at the right time can be a useful tool, she says, but it cannot make up for regularly missing a full night's rest. 'If you find you need a long nap every day,' she says, 'the real question is what is happening to your sleep at night.' She also points out that the best length for a nap may vary from person to person, and suggests that people experiment to find what suits them.