The prevalence of asthma increased significantly beginning in the 1970s until the late-1990s when the increase leveled off. As of 2011, almost 300 million people were affected throughout the world, resulting in about 250,000 deaths per year from asthma attacks. In the US, almost 7% of the population has asthma, about 26 million Americans. Many environmental factors have been associated with asthma including: allergens, air pollution, and other environmental chemicals. Genetics is also involved; if one’s identical twin has asthma, there is a 25% chance the other twin will have it also.
Early treatment with inhaled corticosteroids may prevent declines in lung function. Oral corticosteroids are reserved for severe or uncontrolled asthma. However, a substantial proportion of patients do not achieve control despite oral steroids and other medication. Inadequately controlled patients with severe persistent asthma are at high risk of dying. Anything that may help would be a godsend.
As far as vitamin D goes, for elderly people, both asthma hospitalizations and mortality show increases from January to March. Then, the number of hospitalizations and mortality show a sharp decline beginning in April and a trough in the summer. Also, adult asthma is about 50% more common among African Americans than Caucasian Americans. In the US, a ten degree poleward change in latitude (South to North) is associated with a 2% increase in adult asthma prevalence. Despite these vitamin D clues (seasonality, skin pigmentation, latitude), studies of vitamin D levels and adult asthma have been mixed.
In an open access paper, Doctor Stephanie Korn and colleagues of the Mainz University Hospital in Germany were the first to correlate asthma severity, asthma control, and markers of asthma severity with vitamin D levels.
In this cross sectional analysis, the authors studied 280 consecutive adult asthma patients with mild, moderate, severe or uncontrolled asthma as well as 40 healthy controls. They found the following:
- The mean vitamin D levels in asthma patients (25.6 ng/ml) were the same as controls (26.2 ng/ml).
- However, in the asthma patients, 25(OH)D levels were related to asthma severity (p = 0.046) and asthma control (p = 0.03). For example, only 5% of intermittent asthmatics had levels less than 30 ng/ml but 60% of the poorly controlled asthmatics did.
- Patients with severe and uncontrolled asthma had significantly lower 25(OH)D levels compared with patients with intermittent, mild or controlled asthma (p = 0.014).
- The odds ratio for being vitamin D deficient for patients with severe or uncontrolled asthma was 1.9.
- Vitamin D deficiency was associated with a lower lung function test (FEV1) (p = 0.006). However, several patients with levels above 50 ng/ml had very low FEV1.
- Vitamin D deficiency was associated with higher levels of exhaled nitric oxide (p = 0.023).
- Deficiency was strongly associated with sputum eosinophilia (p = 0.005).
- The use of oral corticosteroids was associated with a 20% higher risk of vitamin D deficiency.
- While 25(OH)D levels varied about 8 ng/ml per season, the authors found no seasonality in symptom severity.
Notice that the average vitamin D levels were the same in asthma patients as in healthy controls. It is important to think about what this means. As asthma has a strong genetic and environmental pollution cause, lower vitamin D levels only exacerbate the disease in those already prone to get it. So, if you have asthma, you may well have the same vitamin D levels as healthy people, but those levels are inadequate to obtain vitamin D’s full benefit.
This is a cross sectional study, meaning that maybe those with the most severe asthma may simply not go outside. While I hope vitamin D is useful in the treatment of asthma, I do not think it will be as effective as it will be in some autoimmune disorders or in cardiovascular diseases. However, even a mild treatment effect would be helpful.
The authors concluded:
“In summary, the present study demonstrates for the first time that 25(OH)D levels are associated with clinical parameters of asthma severity and asthma control in adult patients with asthma. Frequency of vitamin D insufficiency is highest in patients with severe and uncontrolled asthma. This is even more relevant given that the risk of vitamin D insufficiency is significantly increased in patients on oral corticosteroids.”