Longevity is the new health craze, with wealthy people investing millions of dollars in supplements, and some believe you have to be a millionaire to live a long, healthy life, but optimizing a few simple things – especially diet and exercise levels – harnesses the power of the immune system to maintain better health throughout the 80 years we may live.

The immune system fights germs and determines how long it takes to recover from illnesses, and some may try to boost it by taking a multivitaminsupplement or eating an orange.

Dr. Gina Machiyuki, an immunologist, explains to The Telegraph that this narrow view of the immune system covers only a fraction of its wide-ranging impact, not only on health, but on longevity.

What is the immune system?

The immune system is made up of hundreds of different types of cells and signaling molecules, controlled by about 8,000 genes, making it the second most complex system in our bodies, after our brains.

About 70% of the immune system is located in the digestive system, while the rest extends from the surface of the skin to the bone marrow, and from the brain to the big toe.

Immune cells line the entry points into the body – the eyes, nose and mouth – which are coated with a defensive mucus layer designed to capture viruses and bacteria before they can penetrate deep into the body, and protecting against germs is one of the main roles of the immune system.

Dr. Machiyuki explains that our immune system also works in other ways to maintain health: it monitors and eliminates potential cancer cells, protects against autoimmune disorders, and manages the response to allergens.

The immune system plays a role in chronic diseases, with inflammation, triggered by the immune system, thought to be the causative factor in heart disease , diabetes , cancer and dementia.