Ageing and the immune system

The immune system is a complex organisation of cells and molecules acting together to:

  • protect us from harmful, infectious agents
  • aid recovery from injury
  • eliminate abnormal or cancerous cells.

If our immune system overreacts and is poorly regulated, then inflammatory disease can occur. Conversely if it does not react enough, and in the right way, then it fails to protect us from a multitude of dangers, including infections.

In young, healthy people there is generally a good balance between overreaction and under reaction. However, this balance can be lost as we age. In older people, the immune system can fail to protect effectively against infection, and the risk of inflammatory disease rises. As with other parts of the body, most aspects of the immune system deteriorate with age, a process known as immune senescence (biological ageing).

What happens to our immune system as we age?

As people age, the immune system becomes less effective in the following ways.

  • The immune system becomes less able to distinguish self from nonself. As a result, a person can develop antibodies that attack body tissues, meaning that autoimmune diseases, such as rheumatoid arthritis and systemic lupus erythematosus, become more common in older people.
  • Macrophages, specialised cells that help destroy and clear away bacteria and other foreign cells such as cancer cells, work more slowly. This slowdown may be one reason that cancer is more common among older people.
  • T-cells, which are the immune system memory cells, become less able to recognise, remember and respond to the toxins and other foreign substances they have previously encountered.
  • There are fewer white blood cells capable of responding to new challenges to the immune system, such as the threat posed by new viruses. Thus, when older people encounter a new foreign threat, the body is less able to remember and defend against it.
  • Although the amount of antibodies produced in response to the immune system encountering a foreign substance remains about the same overall, the antibodies become less able to attach to the foreign agent. This change may partly explain why illnesses like pneumonia, influenza and other infections are more common among older people and result in death more often. These changes may also partly explain why vaccines are less effective in older people and thus why it is important for older people to keep up to date with immunisations.

Overall, these changes in immune function may contribute to the greater susceptibility of older people to some infections and cancers.

When do the changes occur?

As with many aspects of the human body, there is no single ‘cut off’ point for these changes to occur but instead it is a gradual process. Indeed, the shrinkage of the thymus, an organ that produces a type of immune cell known as T-cells, begins shortly after birth. Over the age of 55 there is also a rise in chronic background inflammation called ‘inflammaging’. This chronic inflammation also reduces the ability to respond to infections or vaccinations.

The implications of having an ageing immune system and an immunodeficiency

People with a primary immune deficiency (PID) have faulty immune systems. The fault can be in any part of the system. Except for the most severe PIDs, some parts will still function but nevertheless deteriorate with advancing age. Generally speaking, people with a normal immune system will have more difficulty in fighting off infections when they are older, and people with untreated PIDs or secondary immunodeficiency will become more ill. This is one reason why the diagnosis of a mild PID or secondary immunodeficiency is often not made until later in life; it is the combination of inborn error and ageing that result in recurrent infection.

Co-existing illnesses and ageing

Many illnesses become more common with advancing age. These include heart disease, diabetes, cancer, stroke and arthritis. An important factor is obesity, which increases inflammation, adversely affects most other conditions and can affect mobility.

Covid-19 and ageing

It is well established that older people have more difficulty fighting off Covid-19. It is important to take whatever steps are necessary to avoid becoming infected. Official advice changes in line with the prevalence of the infection and other factors, such as the ability of the NHS to cope. Current advice should be strictly followed. It is important to maintain good hygiene, wear a face covering, shield or self-isolate if advised, and avoid crowds. Get a test if you develop symptoms. If you receive a positive test result, then inform your GP and immunologist and follow their advice.

If your immunologist has told you to have the annual flu vaccine, then make sure that you get the Covid vaccine too. If you have had adverse reactions to a vaccine in the past, discuss the suitability of the Covid vaccine with your immunology team first. Not responding well to other vaccines is not a contraindication to the currently available Covid vaccines. The benefits to you may be more limited, but any protection is worthwhile.

Staying well as you get older

Keep a positive outlook! Although many physical attributes deteriorate with advancing age, consider celebrating the wealth of experience behind you and embracing the extra time you may have to enjoy your interests.

Keep active. A daily walk benefits both physical and mental health, and is free! It improves circulation, strengthens muscles, helps to keep weight down and adds interest to the day. Try to increase the distance a little each day. You may wish to keep track of your progress by making notes or taking photos.

Eat well. Try to follow the NHS Eat Well guidance, which advises at least five portions of fruit or vegetables a day; wholemeal bread, rice and pasta; moderate dairy and protein foods; and a low intake of sugary and salty foods, such as crisps and biscuits.

Tackle obesity. If you are overweight, don’t despair – help is available. It is really important to keep your weight within the recommended range. This simple BMI calculator will tell you if your weight is in the normal range.

If you are overweight, then you can follow the advice given online. If you are obese, then you may need help from your GP, practice nurse or a dietician to achieve a healthy weight.

Limit your alcohol intake. For advice on drinking, see

Don’t smoke. Smoking makes it harder for your lungs to keep pathogens out and is harmful in many other ways too. Contact your GP practice if you need help to stop smoking.

Try to avoid injuries. A weakened immune system can affect healing, so do what you can to avoid falls. Look at ways to stay safe in the home and garden, consider using a walking pole or stick, and don’t go out in icy conditions.

Vaccinations. As well as the Covid-19 vaccine, make sure you have flu and pneumonia vaccinations, and any other vaccinations that your doctor advises.

More advice is available in our leaflet ‘Stay Healthy’.

Posted February 2021