The cold days of the winter months in particular, see a rise in respiratory tracts infections such as colds and flu. So as winter approaches, it's worth taking steps to boost your immunity.

If you are fit and your immune system is healthy, your body can often fight off infections that cause upper respiratory infections without developing sniffles, coughs, sneezes or sore throats. It is usually when the body is lacking in nutrients, stressed or feeling tired and run down, that symptoms tend to strike.

An Immune-Boosting diet

When it comes to boosting the immune system, diet should always come first. Even a minor lack of some nutrients can lower your immunity and lead to increased risk of disease. For example, viral infections are more likely in those lacking selenium or Vitamin C, both of which help to suppress the activation of viral genes. The cold sore virus (Herpes simplex) and recurrent candida (thrush) are also more common when iron levels are depleted.

To boost immunity, maximize your intake of fruits and vegetables. Try to eat as many as possible raw or lightly steamed to preserve their nutrient content. But winter warmers such as soups and stews are also great for boosting immunity.

essential fatty acids are also important for immune function. They regulate the way immune cells react to chemical signals, known as 'cytokines' and shield immune cells against damaging by-products of your metabolism, such as free radicals. So aim to increase your intake of oily fish, or take fish oil supplements.

probiotics are another beneficial food to include in the diet. Most of or immune defences are found in the wall of the small intestines. Beneficial lactic acid-producing bacteria stimulate immunity here, by secreting natural antibiotics and stimulating the production of interferon, a natural anti-viral agent which helps protect against viral infections. Eat more cultured dairy products like yoghurt and fermented foods like sauerkraut to increase your levels of probiotics.

Stress

When the body is stressed and run down, it is twice as likely to develop symptoms when exposed to a common cold virus. This is thought to be a result of high levels of stress hormones and depleted adrenal glands that interfere with immune function.

exercise

Regular exercise has been proven to boost immunity. The exact mechanism is unknown, but it is probably linked with burning off the effects of stress, so the exercise should therefore be non-competitive.

A study from 2010 found that people who exercised for at least five days a week and felt physically fit and active, cut their chances of having a cold by almost half. Taking regular exercise also cut the severity of symptoms.

One theory is that exercise improves the circulation of immune cells in the blood. The role of these cells is to neutralize pathogens, or disease-causing organisms throughout the body. The better these cells circulate, the more efficient the immune system is at locating and defending against viruses and diseases trying to attack the body.

sleep

Sleep is an essential way of relaxation, regeneration and rejuvenation in which the body secretes substances involved in healing and fighting off disease. It is believed that during sleep the whole body is restored. During deep sleep, the body enters its most intense period of growth, building new proteins and repairing or replacing cells. So getting an adequate amount of good quality sleep is essential for a strong immune system.