The National Jewish Health is one of the top lung hospitals in the US - you can google their website to see what they do - but here is an article about a recent study they did into Vitamin D and asthma.
'Asthmatics with low levels of vitamin D may suffer more severely from the disease than patients with sufficient levels of the vitamin, according to a study conducted by researchers from National Jewish Health in Denver and published in the American Journal of Respiratory and Critical Care Medicine.
""Our findings suggest that low vitamin D levels are associated with worse asthma,"" lead researcher E. Rand Sutherland said.'
'The researchers measured the vitamin D blood levels of 54 asthma patients, along with their lung function, airway hyper-responsiveness and response to steroid drug treatment.
Airway hyper-responsiveness measures the air passages' tendency to constrict, leading to breathing difficulty.
The researchers found that hyper-responsiveness was twice as high in patients with vitamin D levels below 30 nanograms per milliliter, lung function was worse, and the body responded more poorly to steroid therapy.
In addition, the bodies of people with low vitamin D levels produced more or the immune system signaling chemical TNF-alpha, which increases inflammation.
""It may be that vitamin D is acting as a modifier of the immune system or a modifier of steroid response in ways that are relevant to people with asthma,"" Sutherland said.
""There is a potential that restoring normal vitamin D levels in people with asthma may help improve their asthma.""'
'Dr. Michael F. Holick, director of the Vitamin D, Skin and Bone Research Laboratory at Boston University School of Medicine, called this ""a very nice study that confirms previous observations that vitamin D enhances lung function.""
""It is also known that glucocorticoids [steroids] increase the destruction of vitamin D, thus making patients with asthma at higher risk for vitamin D deficiency, which in turn decreases lung function and makes their disease worse,"" he said.
Holick thinks most people, asthmatic or not, get too little D and should take supplements.
""It's pretty clear that you need a minimum of 1,400 and up to 2,000 IU a day, and if you are obese, you probably need at least one and a half to two times as much, because the fat sequesters the vitamin D,"" Holick said. ""We now recognize that you can take up to 10,000 IUs a day and not worry about any untoward toxicity.""'