Some people, it seems, are endowed with a healthy immune system. They never seem to get sick and, if they do get the odd cold, they continue their daily routine and snap out of it in no time flat. Then you see others who barely have to hear the word 'flu or see someone blowing their nose and bam, they've got it!

Is it all in the head? Are you born with a strong immune system to fight off disease? Can you do something about it, if you're not? Anyway, what does it mean to have immunity? Well, a very simple explanation is that there are basically two types: active and passive immunity.

The definition of "immune" is that your body is so strong and resistant to any disease that you will not succumb to it.

Active immunity is considered to be long-lasting and tends to be life-long. If you're in this category then, whenever you're exposed to a disease organism, your immune system will instantly start to produce antibodies to that disease. Furthermore, if you should come into contact with that disease in the future, your immune system will identify it and immediately fight it off with the stored antibodies.

Passive immunity is not inherent in your system. It is when you cannot produce enough antibodies to fight off disease, and get an external boost by injection, medication or nutritional supplements.

Healthy people with an active, innate immunity are usually referred to as being resistant to disease in general. The term immunity is usually applied to general protection against a specific organism. Even if you are generally healthy, you may from time to time need a boost in order to help fight off a virulent strain of a specific infection or virus. The more severe the disease producing organism, the more the passive immunity is applied.

The medical profession recommends boosting your inherent immunity with specific antibodies to fight off a potentially dangerous infection or virus.

A good digestion and healthy appetite are indicators of a strong immunity. "Getting better quickly is a better indicator of immune health," says Dr Dennis Alexander, head of molecular immunology at the Babraham institute in Cambridge.

Immune globulin can be administered to provide immediate protection from specific health threats to those who have a severely impaired or suppressed immune system. For instance, some who may normally have fairly good resistance to disease suddenly realize that their system cannot handle the sudden onslaught of germs in the hospital.

Likewise, the body under stress, i.e. disease or sudden accident, is often not capable to fight off multiple vaccines in one shot.

Judging by the large numbers of people coping with disease, the human system is inherently fragile and cannot handle multiple onslaughts, like the ones discussed above.

Many believe that if you are generally healthy and look after your health, you will only have a mild version of what's going around. "In truth, there's no such thing as a normal immune system," says Angus Dalgleish, professor of oncology at St George's Hospital, London, who researches cancer vaccines. He says the system is naturally very variable.

The rise of allergies, auto-immune diseases (where the body attacks itself) and inflammatory bowel disease are all indicators of immune resistance performing under par.

Both types of acquired immunity respond to peptide sequences called antigens. Antigens help the acquired immune system recognize invading bacteria, viruses and other harmful organisms (pathogens).

Leftovers, non-organic foods, and foods laced with preservatives can severely tax the digestive system. This can, in turn, clog your circulation, and create a sluggish, compromised immune system.

Going to be late, working at night, irregular eating habits, sleeping during the day, and exposing the body to stress and fatigue can all affect the digestion and body rhythms and thus compromise your resistance.

Therefore, be good to yourself. Eating nutritiously and keeping an active, happy lifestyle will go a long way to boosting your immune system. Don't worry; be happy because "a merry heart doeth good like a medicine: but a broken spirit drieth the bones." (Prov. 17: 22)