You may wonder why a professor of immunology would place on his desk a swirling elixir that lists Echinacea, the supposed immune boosting wonder tonic, among its ingredients. Well it's there to illustrate a point.

The human immune system is extraordinary robust - it isn't easy to push off base. If a potion that the teller rings up along with your shaving foam could really fend off a micro-organism, the bugs that cause colds would be history.

Evolutionary fine tuning has produced impressive victories over everything from the bubonic plague to the Spanish flu epidemic of 1918. Alas, these were fleeting leads in a race that won't end, short of human extinction and even something as pesky as the common cold has us in a dead heat today. Every time we make a move, the viruses, pathogens and bacteria think of a countermove.

Few are nastier than HIV, which causes an immunological catastrophe by disarming the very system needed to halt its advance. To keep your immune system fully operational make sure you can answer ‘yes' to the questions that follow. If you can, bugs will start cruising around in search of easier competition, leaving you to perform at top speed.

Are You Eating Enough Kilojoules?

It takes energy to form antibodies and dispatch them to the front lines when germs invade. To see if you're eating enough kilojoules, weigh yourself, without clothes in the morning. Unless you're on a weight-loss program, your body weight shouldn't fluctuate more than a kilogram in either direction in a given week.

If you're losing weight, slowly add healthy foods such as fruit, vegetables and mixed nuts to your diet. If you're gaining, cut back on your portions. Don't skip meals. Dietary variety is vital. Researches have found that even if you eat very little fruit and vegetables, you can maximize the benefits of what you do get in by making sure you eat at least five different colors of produce a day.

Are You Getting Enough Sleep?

Insufficient sleep suppresses the immune system. Even minor sleep disturbances causes a significant drop in the number of cells whose job is to kill invaders. Consider your caffeine intake. If it's excessive, it might be screwing with your immune system. Caffeine suppresses the functions of key immune agents, such as lymphocytes and T-cells. More than four cups of coffee a day is enough to give your immune system an unwelcome jolt.

Are You Getting Enough of the Right Fuel?

The amino acid glutamine is like high octane fuel for your immune cells. Glutamine comes from foods with protein. If you're not eating enough of those, your body will borrow from skeletal muscle, especially if you're working out. Are you working out regularly? If so, keep it up - but down some glutamine. After exercising, try taking five to 15g glutamine powder, or a protein powder.

Are You Drinking Enough Water?

Even overnight your immune reserves are being drained. Hydration is even more important when you're sick. Fluids not only transport nutrients to the illness site, but also take toxins away for disposal. When you wake up, down a glass of water to replenish your system.

Sandra Prior runs her own bodybuilding website at http://bodybuild.rr.nu.