There have been a few interesting articles regarding Vitamin D in the media recently. If you haven't seen them, here's a bit of a summary:
Vitamin D reduces asthma 1
A review of several studies has shown that supplementing with Vitamin D resulted in fewer asthma attacks, with less need for medication. There were also less hospitalizations amongst those people who were supplementing. In other words - taking Vitamin D was found to help prevent severe asthma attacks.
Vitamin D reduces the risk of upper respiratory tract infections 2
Another review looked at how supplementing with Vitamin D might influence susceptibility to suffering from upper respiratory tract infections (URTI) - in other words, coughs/colds, particularly those that go to the chest. Overall, supplementation was found to help prevent these kinds of infections, particularly in people who already had quite low levels.
About Vitamin D
Vitamin D is obtained from the sun and made within your skin (it is known as the 'sunshine vitamin') - so if you work indoors the majority of the time, have naturally dark skin, or if you tend to wear long-sleeved clothing when outside, you may have a more difficult time reaching adequate levels. You can obtain some of this vitamin from foods such as egg yolks, butter, milk, and oily fish (cod, tuna, herring). Not only is it important for a healthy immune system, it also plays a role in bone density, blood clotting, the workings on your muscles and protecting against cancer (particularly colon, breast and melanoma). It is also thought to play a role in weight management, and autoimmune conditions.
We would assume that in our sunny area of south-east Queensland, most of us would have adequate levels of Vitamin D, but by the end of winter, most of us have worn through our supplies and end up being quite deficient. I find that this time of year can be a good time to consider having your Vitamin D levels checked, to see if supplementation might be a good idea before cold & flu season hits. Unfortunately Vitamin D tests are no longer covered for free through Medicare (and the ranges regarded as 'normal' in my opinion are too low anyway).