Retirement is usually sold as the reward at the end of a long working life: no alarm clock, no deadlines, no difficult colleagues and plenty of time to do whatever you like. But research suggests that completely withdrawing from work can have unexpected costs for the brain, body and sense of wellbeing.

Australian doctor and broadcaster Norman Swan has been particularly provocative on this subject. On ABC Radio National he has argued that, on average, cognitive decline often accelerates after retirement. His point is not that everyone should stay in paid employment forever. What seems to matter is whether retirement removes the mental, social and physical demands that work once provided, triggering both mental and physical decline.

Work frequently forces us to solve problems, learn new things, remember information, make decisions and deal with other people. These activities help build and maintain what researchers call “cognitive reserve” – the brain’s ability to cope with age-related change. Swan argues that complex work, especially work involving problem-solving and interaction with others, can help maintain this reserve.

There is research to support this. In a long-running study of British civil servants (the Whitehall II study), decline in verbal memory was 38 per cent faster after retirement than before retirement, even after allowing for normal age-related decline. Other studies have also found faster deterioration in aspects of memory and thinking after people stop working, although the evidence is not uniform.

Another problem is loss of purpose. Employment gives structure to the week and provides goals, responsibilities and a reason to get up in the morning. Retirement can suddenly remove these. For someone whose identity has been strongly tied to a profession, business or career, the question “What do you do?” can become surprisingly difficult to answer.

This is especially important when retirement is involuntary. Swan notes that people pushed abruptly into retirement tend to experience poorer mood than those who control the timing and nature of their transition. Work can be stressful, but it can also provide achievement, status, challenge and a feeling that other people depend on us. Losing those things overnight may leave a psychological vacuum.

Then there is social connection. Much of our everyday contact with other people comes through work – colleagues, customers and professional networks. When work ends, those contacts can disappear quickly. That matters because social isolation is now recognised as a health risk in later life. Research involving older adults has linked persistent loneliness and social isolation with higher rates of illness, disability and mortality.

A British study of retirees found a striking relationship between maintaining social-group memberships and subsequent health. Among people who belonged to two groups before retirement, those who retained both had an estimated 2 per cent risk of dying over the following six years. The risk was 5 per cent among those who lost one group and 12 per cent among those who lost both. This does not prove that losing groups causes death, but it illustrates how important social connection can be.

Physical health can change too. Retirement gives people more time to walk, exercise and play sport, and studies often find an increase in leisure-time exercise. However, this can disguise the loss of incidental activity. Commuting, walking around a workplace and climbing stairs can add up to considerable movement. Swan points out that retirees may exercise deliberately yet still move less overall. Research reviews have also linked retirement with increased sedentary behaviour and, in some groups, weight gain.

So is the answer never to retire? Not necessarily. Retirement can improve wellbeing, particularly for people escaping physically exhausting, dangerous or highly stressful jobs. The evidence is mixed, and Swan emphasises that the effect depends heavily on what kind of work a person was doing and what replaces it.

Perhaps the real danger is not retirement from paid employment but retirement from engagement.

The healthiest retirement may therefore look less like stopping and more like changing gear. Part-time work, consulting, volunteering, caring for others, community leadership, study, learning a language, joining organisations, mentoring or starting a small enterprise can provide many of the same benefits as employment without the pressures of a full-time job.

Swan’s message is essentially “use it or lose it”. The objective in later life should not simply be to avoid work. It should be to preserve challenge, purpose, social connection, movement and curiosity. Financial freedom may allow us to retire from a job, but that shouldn’t mean retiring from life.