Yoga makes you feel good from the inside out.  It is holistic in that it works on improving the health of all of the physiological systems in the body.  The main ones that improve immune function include the circulatory, respiratory, digestive, nervous and endocrine systems.

Breathing techniques (or pranayama) used in yoga increase the lungs capacity by strengthening all of the muscles involved in breathing.  This is particularly important for people who tend to get bronchial conditions such as asthma.  Better lung function has the added benefit of increasing the supply of fresh oxygenated blood to all of your cells, flushing out and supplying fresh nutrients to every cell in your body.

Circulation is also improved with our Asana (physical) practice, which not only increases the blood flow around the body it also helps to stretch the major blood vessels, improving their elasticity. Improved circulation means that your brain will receive more oxygen, improving alertness, memory, and mood. Vital organs receive a steady supply of the nutrients they need for optimal functioning.

Every system, every organ, every cell is guided in its functioning by hormones. The proper growth and functioning of the various parts of the body is possible when there is a balanced secretion of all these hormones. Any imbalance results in disease. Asanas balance the hormonal secretions from the various glands. The twisting and bending positions of the asanas, held for periods of time, place pressure on the various glands of the body, stimulating them and regulating their secretions.

Yoga is one of the only forms of exercise that triggers the para-sympathetic nervous system, which is responsible for the relaxation (or rest, digest and renew) response in the body lowering stress, a major cause of compromised immunity. This helps to balance our nervous system, improves our sleep our ability to respond to stress and our digestion.

Up to 80% of our immune system is located in the digestive tract, so having a healthy gut is crucial to a good immune system.  Many yoga poses stimulate the digestive system, promoting better digestion. However, diet and exercise are not the only factors to contribute to a healthy digestive system. Stress can be a major cause of digestive issues.  Which is why activating the para-sympathetic nervous system is extremely important for digestive health. 

References

http://www.livestrong.com/article/371313-yoga-to-increase-lung-capacity/  

http://www.asm.org.au/yoga/articles/yoga-and-the-circulatory-system

http://www.greaterimmunity.com/Files/digestive_immunity.html

http://www.womenshealthmag.com/health/the-simple-way-to-breathe-easier

http://www.yourbodycenter.com/Glands.htm

Unless I cleverly hide the green vegies it can be hard to get the kids to eat them. I am sure I am not alone!

However I have success with soup.  I think soup is one of the best ways to help the body to fight off winter bugs.  We rarely get sick in our house (touch wood) and if we do we fight it off quickly.  I am a big believer in food as medicine and also eating seasonally.  I think the fruit and vegies that are in season are what your body requires for good health at that time of the year.  Check this guide from the Victorian Farmers Market Association. 

The benefits of eating these vegies are many: they contain many important nutrients such as iron, folate, zinc, potassium, vitamin C, calcium and anti-oxidants..... read more and find my recipe for give 'em greens soup.

This image came into my horizon today and I just had to share.  I have to be honest, winter is not my favourite season, so I have to keep reminding myself to embrace the beautiful things about winter. Learning to dance in the rain. Of course, this is a metaphor for finding the inner strength to embrace all of the elements of your life and finding not only acceptance for the circumstances you are in but joy.  Being thankful for all of life's colours.
This reminds me of mountain pose, Tadasana. When we connect to that inner strength and resilience, just like a mountain, we can weather all seasons. Even if the storms, wind and rain create some instability on the surface, we remain who we are at our very core. Unmoved, stable, connected.  We are often challenged by our own emotions and thoughts that arise when are going through a rough time. Thinking of these emotions as passing bad weather and not getting caught up or attaching to them helps us to remember that "this too shall pass".

It is important to be mindful of the information we are bringing to our awareness on a daily basis.  We are constantly swamped by media, much of it negative, however there is a wealth of positive information out there. The type of information we allow into your lives affects our outlook and as such try to fuel up on positive, healthy information.
This is just one simple way that we can transform our lives.
Let me know if there are any sites or books that you have read that enrich your life by commenting below.