Just as exercise keeps our bodies fit, there are things we can do to keep our immune system in top condition. Everyday complaints such as high levels of stress and not getting enough sleep can weaken the immune system, making it more vulnerable to attack."

Dr Hilary Jones

Our immune systems are comprised of two parts – the innate immune system and the acquired immune system. The cells that carry out the actions of the immune system are the white blood cells.

The Innate Immune system is our first line of defense. Innate immune cells are programmed to recognise foreign compounds and cells and upon detection, they will engulf and kill them. Broadly, these ‘front line defensive troops’ constantly patrol the body and look out for anything that doesn’t belong there.

The acquired immune system is the part of the immune system with ‘memory’. After an infection or a vaccination, the cells will remember the bug’s characteristics and on second exposure to the threat the memory cells will recognise it and generate an immune response involving highly specific weapons. That’s why it is highly unusual to catch measles or the same cold twice.

Our immune systems have evolved over hundreds of thousands of years but changes in our lifestyles over the last few hundred years have left us vulnerable to new threats. So why are our immune systems less effective than they used to be?

1. We live in an unnaturally sterile environment

During most of our time on this planet our environment was teaming with bacterial and viral hazards and our immune systems were constantly challenged. The introduction of synthetic fungicides in 1950 effectively sterilized the food chain, which has unbalanced our immune systems – driving huge increases in allergy – and has left them less able to neutralise new and unexpected threats. This explains why, when we travel to parts of the world where levels of cleanliness are lower than ours, we routinely fall victim to travellers’ ills such as ‘Delhi Belly’.

2. Antibiotics - over-prescription and the rise of the Super Bugs

Too many visits to the doctor end with a needless prescription for an antibiotic – coughs and colds, for example, are usually caused by viruses, which cannot be treated with antibiotics. When antibiotics are prescribed unnecessarily or incorrectly it can give bacteria the chance to develop a resistance to a drug within a surprisingly short period of time. This is how the so-called super bugs, such as MRSA or NDM-1 are created – by developing resistance to many different types of antibiotics.

3. ‘Type B’ Malnutrition

Health researchers are increasingly referring to ‘Type B’ malnutrition. This is not the sort of malnutrition associated with starving people in developing countries, but people in fully developed societies who have adequate calories— (often more than adequate!)—but an inadequate intake of vitamins, minerals and other vital nutrients. For example, the average person has an intake of vitamin D and selenium that is only half the Recommended Daily Allowance (RDA).

4. Crowded Transport

Millions of us endure a daily commute on crowded public transport. This provides ideal conditions for the spread of bacteria and viruses. Added to this, rapid global travel means that a passenger can contract a disease in one continent and arrive in another before the symptoms have even begun to show.

5. The Flu Scare

At the end of 2004 the World Health Organization (WHO) issued a stark warning of the pending flu global epidemic. Antibiotics are no use in treating viral infections, and the right vaccines to protect us against the new strain of flu will take up to 6 months to produce in large amounts.

6. Stress

Most surveys show that a significant number of people report feeling stressed on a regular basis. In chronic or long-term stress our bodies secrete hormones that suppress the immune system.

7. Biological and radiation hazards

Exposure to radiation is another potent cause of immune-suppression and contributes to the increased risk of infections after long-haul air travel.