 A depressed immune system lowers the body's ability to fight off all sorts of diseases, from the simple common cold to cancer. A body with a weak immune system is more susceptible to infections and diseases; infections and diseases then cause further damage to the body and its immune system; this results in a vicious cycle which can cause a persons' health to degenerate. Here are some important dietary and lifestyle tips to help boost one's immunity and break out of this downward spiral. 1. Exercise Exercise benefits the mind and body in many ways and has been shown in many studies to lower one's risk of numerous diseases. Some research, for example, found that people who engaged in regular physical activity were less likely to get cancer than those who did not. Recommendations differ; Michael Murray, ND, recommends at least 30 minutes of aerobic exercise and 5-10 minutes of stretching every day. It is important to listen to one's body and practice common sense -- overexertion too quickly can cause more harm than good. Intense workouts also have the effect of short-term immune suppression. 2. Sleep Sufficient and good-quality rest has a tremendous impact on immunity. Some experts and research suggest at least 7-8 hours of uninterrupted sleep per day, with a person being in bed by 10pm or 11pm. 3. Sunlight Moderate, common-sense exposure to daily sunshine helps the body produce adequate levels of vitamin D, and this hormone plays a critical role in many aspects of human health, including immune function. 4. Water Consumption of an adequate amount of water -- preferably filtered and fluoride free -- every day is necessary for tip-top immune function. A common recommendation is at least eight glasses each day. 5. Manage stress Stress, both mental and emotional, damages the immune system and needs to be properly managed. Daily deep breathing and relaxation exercises help mitigate stress, as do nature walks and meditation. Some people engage in yoga to help deal with stress. Help should be sought if emotional issues cannot be resolved on one's own. 6. Healthy weight Obesity has been implicated as a factor which impairs the immune function. With obesity levels on the rise, this would thus be an increasingly significant contributor to weakened immunity. 7. Avoid refined sugars When it comes to what to avoid to protect one's immune system, refined sugar is among those at the top of the list. Research has suggested that it could impair immunity to quite a significant degree, reducing the function of white blood cells possibly by 50% over a period of up to five hours after ingestion. ( http://www.selfnews.com ) 8. Probiotics Consume yogurt or other foods which contain good bacteria, such as sauerkraut and kimchi, or take a probiotic supplement. A significant portion of immune function actually resides in the gut. Good bacteria also keep the growth of harmful and immunity-damaging microorganisms in check. 9. Avoid immune-damaging elements These include cigarettes, excessive alcohol, MSG, artificial food additives and preservatives, heavy metals, harmful chemicals in household and personal cleaning products, etc. These are known to harm health. Go for natural products as often as possible. 10. Good nutrition Consume plenty of natural whole foods, including vegetables, fruits, whole grains, beans, legumes, seeds and nuts. The body needs a well balanced dietary intake sufficiently stocked with essential nutrients. According to Dr. Murray, 'nutrient deficiency is the most frequent cause of a depressed immune system.' Many clinical and experimental studies suggest that deficiency in just one single nutrient can greatly impair immune-system function. Taking a broad-spectrum multi-supplement or green drinks and supplements such as chlorella, spirulina , barley grass, etc. would be useful in providing the various essential nutrients the body needs. 