I just ran across an article about a study done in Japan regarding Vit D and Influenza A and asthma.  I thought it worth sharing because many people are leery of taking the flu vaccine.
 
This study, set up and run by Dr Mitsuyoshi Urashima of Jikei University of Medicine, noticed that children taking 1,200 units of Vit D3 per day to prevent bone thinning disease were 3 times less likely to report cold and flu symptoms.
 
This led to the setting up of a double-blind, placebo-controlled study on Vit D and flu protection itself.  The results were that 31 of the 167 children taking the placebo pill caught Influenza A but only 18 of the 167 taking Vit D caught the flu - 58% less likely to catch the flu.
 
The surprise in this study was that asthmatics noticed a great reduction in the number of asthma attacks while taking Vit D.  Only 2 of the test group taking Vit D had an attack during the study and 12 of the placebo group had attacks.  Now a new study on just Vit D and asthma is being performed.  Many feel 1200 units of Vit D is still too low.  All are urged to get their vit D3 blood levels checked.  Best results are achieved when you are at the high end of "normal."
 
In a separate article, the America Academy of Pediatric News, May 1, 2010,  advised pregnant women to take 4,000 iu Vit D3 daily to fight infection, disease (flu, colds, etc) in order to deliver healthier, stronger babies.
Source:  American Journal of Clinical Nutrition, March, 2010.
 
my notes:   This dose should continue after delivery and throughout breast feeding at which time the child should receive a daily dose him/herself.  I've read that infants after breast feeding should get 2000 iu a day.  This dose not only raises the immune system's ability to ward off illness, but also virtually guarantees better eyesight -  less myopia.  It would be a good idea to get your infant's blood levels of Vit D tested as well, before beginning to administer a separate dose to the infant.  Have your infant's level tested as well, every 6 mo. Vit D seems to be at the very base of a strong immune system and many, many studies are confirming this, esp in regards to auto-immune diseases, which 1 in 5 Americans suffer from today.