Yes. Asthma, to a great extent, is caused by sun avoidance and consequent vitamin D deficiency.
Asthma, a devastating respiratory illness, is increasing rapidly in the US. The latest statistics I have show that the overall prevalence of asthma increased 75% from 1980-1994, and asthma rates in children under the age of five increased more than 160%.
There is little doubt that the profound increase in asthma in the last few decades has been caused to a great extent by our societal exodus from sunlight exposure along with the increased use of sunscreen, which can inhibit up to 99% of vitamin D production by the skin.
Drs Litonjua and Weiss, in a medical hypothesis presented in 2007, made a strong case for vitamin D deficiency as a major player in the increase in asthma incidence among both children and adults. They hypothesized the following:
1. “… as populations grow more prosperous, more time is spent indoors, and there is less exposure to sunlight, leading to decreased cutaneous vitamin D production.”
2. “Vitamin D has been linked to immune system and lung development in utero, and our epidemiologic studies show that higher vitamin D intake by pregnant mothers reduces asthma risk by as much as 40% in children 3 to 5 years old.”
3. "Vitamin D deficiency has been associated with obesity, African American race (particularly in urban, inner-city settings), and recent immigrants to westernized countries, thus reflecting the epidemiologic patterns observed in the asthma epidemic."
Other research demonstrates that vitamin D reduces the production of inflammatory chemicals (chemokines) in the respiratory passages, which would dampen the asthmatic response.
Another study assessed the asthma risk of children whose mothers had the highest vitamin D consumption during pregnancy, and compared them to children whose mother had the lowest levels. The high-vitamin D group showed an impressive reduced risk of asthma of 52-67%. The researchers believe that inadequate vitamin D levels in the fetus leads to improper development of the lungs and immune system.
Still other research, conducted on three-year old children whose mothers were in the highest quartile (fourth) of vitamin D consumption during pregnancy, showed them to have a 61% reduced risk of a “recurrent wheeze,” a symptom of asthma, when compared to those whose mothers were in the lowest quartile. Each 100-IU increase in vitamin D consumption resulted in a 19% risk reduction. That's about the amount that could be produced in the summer sunlight in one minute, or a good tanning bed in half a minute! How sad that these women have been frightened out of the sunlight, the natural way to produce vast quantities of vitamin D.
 Centers for Disease Control. Surveillance for Asthma - United States, 1960-1995, MMWR. 1998; 47 (SS-1).
 Matsuoka, L. et al. sunscreens suppress cutaneous vitamin D3 synthesis. Journal Clini Endocrinol Metab 1987; 64:1165-68.
 Litonjua AA, Weiss ST. Is vitamin D deficiency to blame for the asthma epidemic? J Allergy Clin Immunol 2007;120:1031–1035.
 Banerjee, A. et al. Vitamin D and glucocorticoids differentially modulate chemokine expression in human airway smooth muscle cells. Br J Pharmacol 2008; 155: 84–92.
 Devereux, G. et al. Maternal vitamin D intake and early childhood wheezing. Am J Clin Nutr 2007;85:853-59.
 Camargo, C. et al. Maternal intake of vitamin D during pregnancy and risk of recurrent wheeze in children at 3 y. Am J Clin Nutr 2007;85:788-95.